These patches are taken from the LUOv4 series [1] and address recent comments from Pratyush.
They apply onto mm/mm-nonmm-unstable.
This series refactors the KHO framework to better support in-kernel users like the upcoming LUO. The current design, which relies on a notifier chain and debugfs for control, is too restrictive for direct programmatic use.
The core of this rework is the removal of the notifier chain in favor of a direct registration API. This decouples clients from the shutdown-time finalization sequence, allowing them to manage their preserved state more flexibly and at any time.
In support of this new model, this series also: - Exports kho_finalize() and kho_abort() for programmatic control. - Makes the debugfs interface optional. - Introduces APIs to unpreserve memory and fixes a bug in the abort path where client state was being incorrectly discarded. Note that this is an interim step, as a more comprehensive fix is planned as part of the stateless KHO work [2]. - Moves all KHO code into a new kernel/liveupdate/ directory to consolidate live update components.
[1] https://lore.kernel.org/all/20250929010321.3462457-1-pasha.tatashin@soleen.c... [2] https://lore.kernel.org/all/20251001011941.1513050-1-jasonmiu@google.com
Mike Rapoport (Microsoft) (1): kho: drop notifiers
Pasha Tatashin (6): kho: allow to drive kho from within kernel kho: make debugfs interface optional kho: add interfaces to unpreserve folios and page ranges kho: don't unpreserve memory during abort liveupdate: kho: move to kernel/liveupdate liveupdate: kho: move kho debugfs directory to liveupdate
Documentation/core-api/kho/concepts.rst | 2 +- MAINTAINERS | 3 +- include/linux/kexec_handover.h | 53 +- init/Kconfig | 2 + kernel/Kconfig.kexec | 24 - kernel/Makefile | 3 +- kernel/kexec_handover_internal.h | 16 - kernel/liveupdate/Kconfig | 39 ++ kernel/liveupdate/Makefile | 5 + kernel/{ => liveupdate}/kexec_handover.c | 513 +++++++----------- .../{ => liveupdate}/kexec_handover_debug.c | 0 kernel/liveupdate/kexec_handover_debugfs.c | 219 ++++++++ kernel/liveupdate/kexec_handover_internal.h | 56 ++ lib/test_kho.c | 30 +- mm/memblock.c | 62 +-- tools/testing/selftests/kho/init.c | 2 +- tools/testing/selftests/kho/vmtest.sh | 1 + 17 files changed, 576 insertions(+), 454 deletions(-) delete mode 100644 kernel/kexec_handover_internal.h create mode 100644 kernel/liveupdate/Kconfig create mode 100644 kernel/liveupdate/Makefile rename kernel/{ => liveupdate}/kexec_handover.c (80%) rename kernel/{ => liveupdate}/kexec_handover_debug.c (100%) create mode 100644 kernel/liveupdate/kexec_handover_debugfs.c create mode 100644 kernel/liveupdate/kexec_handover_internal.h
base-commit: 4d90027271cfa0d89473d1e288af52fda9a74935
Allow kernel to drive finalize and abort without requiring triggers from the userspace.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com Reviewed-by: Pratyush Yadav pratyush@kernel.org --- include/linux/kexec_handover.h | 15 +++++++ kernel/kexec_handover.c | 75 +++++++++++++++++++++------------- 2 files changed, 61 insertions(+), 29 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 25042c1d8d54..04d0108db98e 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -67,6 +67,10 @@ void kho_memory_init(void);
void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, u64 scratch_len); + +int kho_finalize(void); +int kho_abort(void); + #else static inline bool kho_is_enabled(void) { @@ -139,6 +143,17 @@ static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, u64 scratch_len) { } + +static inline int kho_finalize(void) +{ + return -EOPNOTSUPP; +} + +static inline int kho_abort(void) +{ + return -EOPNOTSUPP; +} + #endif /* CONFIG_KEXEC_HANDOVER */
#endif /* LINUX_KEXEC_HANDOVER_H */ diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index de4466b47455..6458f369a346 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -1087,7 +1087,7 @@ static int kho_out_update_debugfs_fdt(void) return err; }
-static int kho_abort(void) +static int __kho_abort(void) { int err; unsigned long order; @@ -1120,7 +1120,27 @@ static int kho_abort(void) return err; }
-static int kho_finalize(void) +int kho_abort(void) +{ + int ret = 0; + + if (!kho_enable) + return -EOPNOTSUPP; + + guard(mutex)(&kho_out.lock); + if (!kho_out.finalized) + return -ENOENT; + + ret = __kho_abort(); + if (ret) + return ret; + + kho_out.finalized = false; + + return kho_out_update_debugfs_fdt(); +} + +static int __kho_finalize(void) { int err = 0; u64 *preserved_mem_map; @@ -1163,12 +1183,32 @@ static int kho_finalize(void) abort: if (err) { pr_err("Failed to convert KHO state tree: %d\n", err); - kho_abort(); + __kho_abort(); }
return err; }
+int kho_finalize(void) +{ + int ret; + + if (!kho_enable) + return -EOPNOTSUPP; + + guard(mutex)(&kho_out.lock); + if (kho_out.finalized) + return -EEXIST; + + ret = __kho_finalize(); + if (ret) + return ret; + + kho_out.finalized = true; + + return kho_out_update_debugfs_fdt(); +} + static int kho_out_finalize_get(void *data, u64 *val) { mutex_lock(&kho_out.lock); @@ -1178,35 +1218,12 @@ static int kho_out_finalize_get(void *data, u64 *val) return 0; }
-static int kho_out_finalize_set(void *data, u64 _val) +static int kho_out_finalize_set(void *data, u64 val) { - int ret = 0; - bool val = !!_val; - - mutex_lock(&kho_out.lock); - - if (val == kho_out.finalized) { - if (kho_out.finalized) - ret = -EEXIST; - else - ret = -ENOENT; - goto unlock; - } - if (val) - ret = kho_finalize(); + return kho_finalize(); else - ret = kho_abort(); - - if (ret) - goto unlock; - - kho_out.finalized = val; - ret = kho_out_update_debugfs_fdt(); - -unlock: - mutex_unlock(&kho_out.lock); - return ret; + return kho_abort(); }
DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
On Tue, Oct 21, 2025 at 08:57:13PM -0400, Pasha Tatashin wrote:
Allow kernel to drive finalize and abort without requiring triggers from the userspace.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com Reviewed-by: Pratyush Yadav pratyush@kernel.org
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
include/linux/kexec_handover.h | 15 +++++++ kernel/kexec_handover.c | 75 +++++++++++++++++++++------------- 2 files changed, 61 insertions(+), 29 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 25042c1d8d54..04d0108db98e 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -67,6 +67,10 @@ void kho_memory_init(void); void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, u64 scratch_len);
+int kho_finalize(void); +int kho_abort(void);
#else static inline bool kho_is_enabled(void) { @@ -139,6 +143,17 @@ static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, u64 scratch_len) { }
+static inline int kho_finalize(void) +{
- return -EOPNOTSUPP;
+}
+static inline int kho_abort(void) +{
- return -EOPNOTSUPP;
+}
#endif /* CONFIG_KEXEC_HANDOVER */ #endif /* LINUX_KEXEC_HANDOVER_H */ diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index de4466b47455..6458f369a346 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -1087,7 +1087,7 @@ static int kho_out_update_debugfs_fdt(void) return err; } -static int kho_abort(void) +static int __kho_abort(void) { int err; unsigned long order; @@ -1120,7 +1120,27 @@ static int kho_abort(void) return err; } -static int kho_finalize(void) +int kho_abort(void) +{
- int ret = 0;
- if (!kho_enable)
return -EOPNOTSUPP;- guard(mutex)(&kho_out.lock);
- if (!kho_out.finalized)
return -ENOENT;- ret = __kho_abort();
- if (ret)
return ret;- kho_out.finalized = false;
- return kho_out_update_debugfs_fdt();
+}
+static int __kho_finalize(void) { int err = 0; u64 *preserved_mem_map; @@ -1163,12 +1183,32 @@ static int kho_finalize(void) abort: if (err) { pr_err("Failed to convert KHO state tree: %d\n", err);
kho_abort();
__kho_abort();return err; } +int kho_finalize(void) +{
- int ret;
- if (!kho_enable)
return -EOPNOTSUPP;- guard(mutex)(&kho_out.lock);
- if (kho_out.finalized)
return -EEXIST;- ret = __kho_finalize();
- if (ret)
return ret;- kho_out.finalized = true;
- return kho_out_update_debugfs_fdt();
+}
static int kho_out_finalize_get(void *data, u64 *val) { mutex_lock(&kho_out.lock); @@ -1178,35 +1218,12 @@ static int kho_out_finalize_get(void *data, u64 *val) return 0; } -static int kho_out_finalize_set(void *data, u64 _val) +static int kho_out_finalize_set(void *data, u64 val) {
- int ret = 0;
- bool val = !!_val;
- mutex_lock(&kho_out.lock);
- if (val == kho_out.finalized) {
if (kho_out.finalized)ret = -EEXIST;elseret = -ENOENT;goto unlock;- }
- if (val)
ret = kho_finalize();
return kho_finalize();
ret = kho_abort();- if (ret)
goto unlock;- kho_out.finalized = val;
- ret = kho_out_update_debugfs_fdt();
-unlock:
- mutex_unlock(&kho_out.lock);
- return ret;
return kho_abort();} DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get, -- 2.51.0.915.g61a8936c21-goog
Currently, KHO is controlled via debugfs interface, but once LUO is introduced, it can control KHO, and the debug interface becomes optional.
Add a separate config CONFIG_KEXEC_HANDOVER_DEBUGFS that enables the debugfs interface, and allows to inspect the tree.
Move all debugfs related code to a new file to keep the .c files clear of ifdefs.
Co-developed-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- MAINTAINERS | 3 +- kernel/Kconfig.kexec | 10 ++ kernel/Makefile | 1 + kernel/kexec_handover.c | 226 +++----------------------- kernel/kexec_handover_debugfs.c | 216 ++++++++++++++++++++++++ kernel/kexec_handover_internal.h | 37 +++++ tools/testing/selftests/kho/vmtest.sh | 1 + 7 files changed, 286 insertions(+), 208 deletions(-) create mode 100644 kernel/kexec_handover_debugfs.c
diff --git a/MAINTAINERS b/MAINTAINERS index 6c0f154cb76d..0a6ba2717caa 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13774,13 +13774,14 @@ KEXEC HANDOVER (KHO) M: Alexander Graf graf@amazon.com M: Mike Rapoport rppt@kernel.org M: Changyuan Lyu changyuanl@google.com +M: Pasha Tatashin pasha.tatashin@soleen.com L: kexec@lists.infradead.org L: linux-mm@kvack.org S: Maintained F: Documentation/admin-guide/mm/kho.rst F: Documentation/core-api/kho/* F: include/linux/kexec_handover.h -F: kernel/kexec_handover.c +F: kernel/kexec_handover* F: tools/testing/selftests/kho/
KEYS-ENCRYPTED diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec index c94d36b5fcd9..9308a0fb1419 100644 --- a/kernel/Kconfig.kexec +++ b/kernel/Kconfig.kexec @@ -118,6 +118,16 @@ config KEXEC_HANDOVER_DEBUG scenarios and the extra code might be adding overhead it is only optionally enabled.
+config KEXEC_HANDOVER_DEBUGFS + bool "kexec handover debugfs interface" + depends on KEXEC_HANDOVER + depends on DEBUG_FS + help + Allow to control kexec handover device tree via debugfs + interface, i.e. finalize the state or aborting the finalization. + Also, enables inspecting the KHO fdt trees with the debugfs binary + blobs. + config CRASH_DUMP bool "kernel crash dumps" default ARCH_DEFAULT_CRASH_DUMP diff --git a/kernel/Makefile b/kernel/Makefile index 9fe722305c9b..2cf7909a74e5 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -84,6 +84,7 @@ obj-$(CONFIG_KEXEC_FILE) += kexec_file.o obj-$(CONFIG_KEXEC_ELF) += kexec_elf.o obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o +obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS) += kexec_handover_debugfs.o obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o obj-$(CONFIG_COMPAT) += compat.o obj-$(CONFIG_CGROUPS) += cgroup/ diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 6458f369a346..da071277d85e 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -11,7 +11,6 @@ #include <linux/cleanup.h> #include <linux/cma.h> #include <linux/count_zeros.h> -#include <linux/debugfs.h> #include <linux/kexec.h> #include <linux/kexec_handover.h> #include <linux/libfdt.h> @@ -30,6 +29,7 @@ */ #include "../mm/internal.h" #include "kexec_internal.h" +#include "kexec_handover_internal.h"
#define KHO_FDT_COMPATIBLE "kho-v1" #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map" @@ -105,8 +105,6 @@ struct khoser_mem_chunk;
struct kho_serialization { struct page *fdt; - struct list_head fdt_list; - struct dentry *sub_fdt_dir; struct kho_mem_track track; /* First chunk of serialized preserved memory map */ struct khoser_mem_chunk *preserved_mem_map; @@ -114,20 +112,16 @@ struct kho_serialization {
struct kho_out { struct blocking_notifier_head chain_head; - - struct dentry *dir; - struct mutex lock; /* protects KHO FDT finalization */ - struct kho_serialization ser; bool finalized; + struct kho_debugfs dbg; };
static struct kho_out kho_out = { .chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head), .lock = __MUTEX_INITIALIZER(kho_out.lock), .ser = { - .fdt_list = LIST_HEAD_INIT(kho_out.ser.fdt_list), .track = { .orders = XARRAY_INIT(kho_out.ser.track.orders, 0), }, @@ -477,8 +471,8 @@ static void __init kho_mem_deserialize(const void *fdt) * area for early allocations that happen before page allocator is * initialized. */ -static struct kho_scratch *kho_scratch; -static unsigned int kho_scratch_cnt; +struct kho_scratch *kho_scratch; +unsigned int kho_scratch_cnt;
/* * The scratch areas are scaled by default as percent of memory allocated from @@ -674,37 +668,6 @@ static void __init kho_reserve_scratch(void) kho_enable = false; }
-struct fdt_debugfs { - struct list_head list; - struct debugfs_blob_wrapper wrapper; - struct dentry *file; -}; - -static int kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir, - const char *name, const void *fdt) -{ - struct fdt_debugfs *f; - struct dentry *file; - - f = kmalloc(sizeof(*f), GFP_KERNEL); - if (!f) - return -ENOMEM; - - f->wrapper.data = (void *)fdt; - f->wrapper.size = fdt_totalsize(fdt); - - file = debugfs_create_blob(name, 0400, dir, &f->wrapper); - if (IS_ERR(file)) { - kfree(f); - return PTR_ERR(file); - } - - f->file = file; - list_add(&f->list, list); - - return 0; -} - /** * kho_add_subtree - record the physical address of a sub FDT in KHO root tree. * @ser: serialization control object passed by KHO notifiers. @@ -716,7 +679,8 @@ static int kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir, * by KHO for the new kernel to retrieve it after kexec. * * A debugfs blob entry is also created at - * ``/sys/kernel/debug/kho/out/sub_fdts/@name``. + * ``/sys/kernel/debug/kho/out/sub_fdts/@name`` when kernel is configured with + * CONFIG_KEXEC_HANDOVER_DEBUGFS * * Return: 0 on success, error code on failure */ @@ -733,7 +697,7 @@ int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) if (err) return err;
- return kho_debugfs_fdt_add(&ser->fdt_list, ser->sub_fdt_dir, name, fdt); + return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false); } EXPORT_SYMBOL_GPL(kho_add_subtree);
@@ -1064,29 +1028,6 @@ void *kho_restore_vmalloc(const struct kho_vmalloc *preservation) } EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
-/* Handling for debug/kho/out */ - -static struct dentry *debugfs_root; - -static int kho_out_update_debugfs_fdt(void) -{ - int err = 0; - struct fdt_debugfs *ff, *tmp; - - if (kho_out.finalized) { - err = kho_debugfs_fdt_add(&kho_out.ser.fdt_list, kho_out.dir, - "fdt", page_to_virt(kho_out.ser.fdt)); - } else { - list_for_each_entry_safe(ff, tmp, &kho_out.ser.fdt_list, list) { - debugfs_remove(ff->file); - list_del(&ff->list); - kfree(ff); - } - } - - return err; -} - static int __kho_abort(void) { int err; @@ -1136,8 +1077,9 @@ int kho_abort(void) return ret;
kho_out.finalized = false; + kho_debugfs_cleanup(&kho_out.dbg);
- return kho_out_update_debugfs_fdt(); + return 0; }
static int __kho_finalize(void) @@ -1206,92 +1148,23 @@ int kho_finalize(void)
kho_out.finalized = true;
- return kho_out_update_debugfs_fdt(); + return kho_debugfs_fdt_add(&kho_out.dbg, "fdt", + page_to_virt(kho_out.ser.fdt), true); }
-static int kho_out_finalize_get(void *data, u64 *val) +bool kho_finalized(void) { - mutex_lock(&kho_out.lock); - *val = kho_out.finalized; - mutex_unlock(&kho_out.lock); - - return 0; -} - -static int kho_out_finalize_set(void *data, u64 val) -{ - if (val) - return kho_finalize(); - else - return kho_abort(); -} - -DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get, - kho_out_finalize_set, "%llu\n"); - -static int scratch_phys_show(struct seq_file *m, void *v) -{ - for (int i = 0; i < kho_scratch_cnt; i++) - seq_printf(m, "0x%llx\n", kho_scratch[i].addr); - - return 0; -} -DEFINE_SHOW_ATTRIBUTE(scratch_phys); - -static int scratch_len_show(struct seq_file *m, void *v) -{ - for (int i = 0; i < kho_scratch_cnt; i++) - seq_printf(m, "0x%llx\n", kho_scratch[i].size); - - return 0; -} -DEFINE_SHOW_ATTRIBUTE(scratch_len); - -static __init int kho_out_debugfs_init(void) -{ - struct dentry *dir, *f, *sub_fdt_dir; - - dir = debugfs_create_dir("out", debugfs_root); - if (IS_ERR(dir)) - return -ENOMEM; - - sub_fdt_dir = debugfs_create_dir("sub_fdts", dir); - if (IS_ERR(sub_fdt_dir)) - goto err_rmdir; - - f = debugfs_create_file("scratch_phys", 0400, dir, NULL, - &scratch_phys_fops); - if (IS_ERR(f)) - goto err_rmdir; - - f = debugfs_create_file("scratch_len", 0400, dir, NULL, - &scratch_len_fops); - if (IS_ERR(f)) - goto err_rmdir; - - f = debugfs_create_file("finalize", 0600, dir, NULL, - &fops_kho_out_finalize); - if (IS_ERR(f)) - goto err_rmdir; - - kho_out.dir = dir; - kho_out.ser.sub_fdt_dir = sub_fdt_dir; - return 0; - -err_rmdir: - debugfs_remove_recursive(dir); - return -ENOENT; + guard(mutex)(&kho_out.lock); + return kho_out.finalized; }
struct kho_in { - struct dentry *dir; phys_addr_t fdt_phys; phys_addr_t scratch_phys; - struct list_head fdt_list; + struct kho_debugfs dbg; };
static struct kho_in kho_in = { - .fdt_list = LIST_HEAD_INIT(kho_in.fdt_list), };
static const void *kho_get_fdt(void) @@ -1355,56 +1228,6 @@ int kho_retrieve_subtree(const char *name, phys_addr_t *phys) } EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
-/* Handling for debugfs/kho/in */ - -static __init int kho_in_debugfs_init(const void *fdt) -{ - struct dentry *sub_fdt_dir; - int err, child; - - kho_in.dir = debugfs_create_dir("in", debugfs_root); - if (IS_ERR(kho_in.dir)) - return PTR_ERR(kho_in.dir); - - sub_fdt_dir = debugfs_create_dir("sub_fdts", kho_in.dir); - if (IS_ERR(sub_fdt_dir)) { - err = PTR_ERR(sub_fdt_dir); - goto err_rmdir; - } - - err = kho_debugfs_fdt_add(&kho_in.fdt_list, kho_in.dir, "fdt", fdt); - if (err) - goto err_rmdir; - - fdt_for_each_subnode(child, fdt, 0) { - int len = 0; - const char *name = fdt_get_name(fdt, child, NULL); - const u64 *fdt_phys; - - fdt_phys = fdt_getprop(fdt, child, "fdt", &len); - if (!fdt_phys) - continue; - if (len != sizeof(*fdt_phys)) { - pr_warn("node `%s`'s prop `fdt` has invalid length: %d\n", - name, len); - continue; - } - err = kho_debugfs_fdt_add(&kho_in.fdt_list, sub_fdt_dir, name, - phys_to_virt(*fdt_phys)); - if (err) { - pr_warn("failed to add fdt `%s` to debugfs: %d\n", name, - err); - continue; - } - } - - return 0; - -err_rmdir: - debugfs_remove_recursive(kho_in.dir); - return err; -} - static __init int kho_init(void) { int err = 0; @@ -1419,27 +1242,16 @@ static __init int kho_init(void) goto err_free_scratch; }
- debugfs_root = debugfs_create_dir("kho", NULL); - if (IS_ERR(debugfs_root)) { - err = -ENOENT; + err = kho_debugfs_init(); + if (err) goto err_free_fdt; - }
- err = kho_out_debugfs_init(); + err = kho_out_debugfs_init(&kho_out.dbg); if (err) goto err_free_fdt;
if (fdt) { - err = kho_in_debugfs_init(fdt); - /* - * Failure to create /sys/kernel/debug/kho/in does not prevent - * reviving state from KHO and setting up KHO for the next - * kexec. - */ - if (err) - pr_err("failed exposing handover FDT in debugfs: %d\n", - err); - + kho_in_debugfs_init(&kho_in.dbg, fdt); return 0; }
diff --git a/kernel/kexec_handover_debugfs.c b/kernel/kexec_handover_debugfs.c new file mode 100644 index 000000000000..a91b279f1b23 --- /dev/null +++ b/kernel/kexec_handover_debugfs.c @@ -0,0 +1,216 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * kexec_handover_debugfs.c - kexec handover debugfs interfaces + * Copyright (C) 2023 Alexander Graf graf@amazon.com + * Copyright (C) 2025 Microsoft Corporation, Mike Rapoport rppt@kernel.org + * Copyright (C) 2025 Google LLC, Changyuan Lyu changyuanl@google.com + * Copyright (C) 2025 Google LLC, Pasha Tatashin pasha.tatashin@soleen.com + */ + +#define pr_fmt(fmt) "KHO: " fmt + +#include <linux/init.h> +#include <linux/io.h> +#include <linux/libfdt.h> +#include <linux/mm.h> +#include "kexec_handover_internal.h" + +static struct dentry *debugfs_root; + +struct fdt_debugfs { + struct list_head list; + struct debugfs_blob_wrapper wrapper; + struct dentry *file; +}; + +static int __kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir, + const char *name, const void *fdt) +{ + struct fdt_debugfs *f; + struct dentry *file; + + f = kmalloc(sizeof(*f), GFP_KERNEL); + if (!f) + return -ENOMEM; + + f->wrapper.data = (void *)fdt; + f->wrapper.size = fdt_totalsize(fdt); + + file = debugfs_create_blob(name, 0400, dir, &f->wrapper); + if (IS_ERR(file)) { + kfree(f); + return PTR_ERR(file); + } + + f->file = file; + list_add(&f->list, list); + + return 0; +} + +int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, + const void *fdt, bool root) +{ + struct dentry *dir; + + if (root) + dir = dbg->dir; + else + dir = dbg->sub_fdt_dir; + + return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt); +} + +void kho_debugfs_cleanup(struct kho_debugfs *dbg) +{ + struct fdt_debugfs *ff, *tmp; + + list_for_each_entry_safe(ff, tmp, &dbg->fdt_list, list) { + debugfs_remove(ff->file); + list_del(&ff->list); + kfree(ff); + } +} + +static int kho_out_finalize_get(void *data, u64 *val) +{ + *val = kho_finalized(); + + return 0; +} + +static int kho_out_finalize_set(void *data, u64 val) +{ + if (val) + return kho_finalize(); + else + return kho_abort(); +} + +DEFINE_DEBUGFS_ATTRIBUTE(kho_out_finalize_fops, kho_out_finalize_get, + kho_out_finalize_set, "%llu\n"); + +static int scratch_phys_show(struct seq_file *m, void *v) +{ + for (int i = 0; i < kho_scratch_cnt; i++) + seq_printf(m, "0x%llx\n", kho_scratch[i].addr); + + return 0; +} +DEFINE_SHOW_ATTRIBUTE(scratch_phys); + +static int scratch_len_show(struct seq_file *m, void *v) +{ + for (int i = 0; i < kho_scratch_cnt; i++) + seq_printf(m, "0x%llx\n", kho_scratch[i].size); + + return 0; +} +DEFINE_SHOW_ATTRIBUTE(scratch_len); + +__init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt) +{ + struct dentry *dir, *sub_fdt_dir; + int err, child; + + INIT_LIST_HEAD(&dbg->fdt_list); + + dir = debugfs_create_dir("in", debugfs_root); + if (IS_ERR(dir)) { + err = PTR_ERR(dir); + goto err_out; + } + + sub_fdt_dir = debugfs_create_dir("sub_fdts", dir); + if (IS_ERR(sub_fdt_dir)) { + err = PTR_ERR(sub_fdt_dir); + goto err_rmdir; + } + + err = __kho_debugfs_fdt_add(&dbg->fdt_list, dir, "fdt", fdt); + if (err) + goto err_rmdir; + + fdt_for_each_subnode(child, fdt, 0) { + int len = 0; + const char *name = fdt_get_name(fdt, child, NULL); + const u64 *fdt_phys; + + fdt_phys = fdt_getprop(fdt, child, "fdt", &len); + if (!fdt_phys) + continue; + if (len != sizeof(*fdt_phys)) { + pr_warn("node %s prop fdt has invalid length: %d\n", + name, len); + continue; + } + err = __kho_debugfs_fdt_add(&dbg->fdt_list, sub_fdt_dir, name, + phys_to_virt(*fdt_phys)); + if (err) { + pr_warn("failed to add fdt %s to debugfs: %d\n", name, + err); + continue; + } + } + + dbg->dir = dir; + dbg->sub_fdt_dir = sub_fdt_dir; + + return; +err_rmdir: + debugfs_remove_recursive(dir); +err_out: + /* + * Failure to create /sys/kernel/debug/kho/in does not prevent + * reviving state from KHO and setting up KHO for the next + * kexec. + */ + if (err) + pr_err("failed exposing handover FDT in debugfs: %d\n", err); +} + +__init int kho_out_debugfs_init(struct kho_debugfs *dbg) +{ + struct dentry *dir, *f, *sub_fdt_dir; + + INIT_LIST_HEAD(&dbg->fdt_list); + + dir = debugfs_create_dir("out", debugfs_root); + if (IS_ERR(dir)) + return -ENOMEM; + + sub_fdt_dir = debugfs_create_dir("sub_fdts", dir); + if (IS_ERR(sub_fdt_dir)) + goto err_rmdir; + + f = debugfs_create_file("scratch_phys", 0400, dir, NULL, + &scratch_phys_fops); + if (IS_ERR(f)) + goto err_rmdir; + + f = debugfs_create_file("scratch_len", 0400, dir, NULL, + &scratch_len_fops); + if (IS_ERR(f)) + goto err_rmdir; + + f = debugfs_create_file("finalize", 0600, dir, NULL, + &kho_out_finalize_fops); + if (IS_ERR(f)) + goto err_rmdir; + + dbg->dir = dir; + dbg->sub_fdt_dir = sub_fdt_dir; + return 0; + +err_rmdir: + debugfs_remove_recursive(dir); + return -ENOENT; +} + +__init int kho_debugfs_init(void) +{ + debugfs_root = debugfs_create_dir("kho", NULL); + if (IS_ERR(debugfs_root)) + return -ENOENT; + return 0; +} diff --git a/kernel/kexec_handover_internal.h b/kernel/kexec_handover_internal.h index 05e9720ba7b9..28c0e971613d 100644 --- a/kernel/kexec_handover_internal.h +++ b/kernel/kexec_handover_internal.h @@ -2,8 +2,45 @@ #ifndef LINUX_KEXEC_HANDOVER_INTERNAL_H #define LINUX_KEXEC_HANDOVER_INTERNAL_H
+#include <linux/kexec_handover.h> +#include <linux/list.h> #include <linux/types.h>
+#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS +#include <linux/debugfs.h> + +struct kho_debugfs { + struct dentry *dir; + struct dentry *sub_fdt_dir; + struct list_head fdt_list; +}; + +#else +struct kho_debugfs {}; +#endif + +extern struct kho_scratch *kho_scratch; +extern unsigned int kho_scratch_cnt; + +bool kho_finalized(void); + +#ifdef CONFIG_KEXEC_HANDOVER_DEBUGFS +int kho_debugfs_init(void); +void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt); +int kho_out_debugfs_init(struct kho_debugfs *dbg); +int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, + const void *fdt, bool root); +void kho_debugfs_cleanup(struct kho_debugfs *dbg); +#else +static inline int kho_debugfs_init(void) { return 0; } +static inline void kho_in_debugfs_init(struct kho_debugfs *dbg, + const void *fdt) { } +static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; } +static inline int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, + const void *fdt, bool root) { return 0; } +static inline void kho_debugfs_cleanup(struct kho_debugfs *dbg) {} +#endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */ + #ifdef CONFIG_KEXEC_HANDOVER_DEBUG bool kho_scratch_overlap(phys_addr_t phys, size_t size); #else diff --git a/tools/testing/selftests/kho/vmtest.sh b/tools/testing/selftests/kho/vmtest.sh index 3f6c17166846..49fdac8e8b15 100755 --- a/tools/testing/selftests/kho/vmtest.sh +++ b/tools/testing/selftests/kho/vmtest.sh @@ -59,6 +59,7 @@ function build_kernel() { tee "$kconfig" > "$kho_config" <<EOF CONFIG_BLK_DEV_INITRD=y CONFIG_KEXEC_HANDOVER=y +CONFIG_KEXEC_HANDOVER_DEBUGFS=y CONFIG_TEST_KEXEC_HANDOVER=y CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_VM=y
On Tue, Oct 21 2025, Pasha Tatashin wrote:
Currently, KHO is controlled via debugfs interface, but once LUO is introduced, it can control KHO, and the debug interface becomes optional.
Add a separate config CONFIG_KEXEC_HANDOVER_DEBUGFS that enables the debugfs interface, and allows to inspect the tree.
Move all debugfs related code to a new file to keep the .c files clear of ifdefs.
Co-developed-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
Reviewed-by: Pratyush Yadav pratyush@kernel.org
[...]
From: "Mike Rapoport (Microsoft)" rppt@kernel.org
The KHO framework uses a notifier chain as the mechanism for clients to participate in the finalization process. While this works for a single, central state machine, it is too restrictive for kernel-internal components like pstore/reserve_mem or IMA. These components need a simpler, direct way to register their state for preservation (e.g., during their initcall) without being part of a complex, shutdown-time notifier sequence. The notifier model forces all participants into a single finalization flow and makes direct preservation from an arbitrary context difficult. This patch refactors the client participation model by removing the notifier chain and introducing a direct API for managing FDT subtrees.
The core kho_finalize() and kho_abort() state machine remains, but clients now register their data with KHO beforehand.
Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Co-developed-by: Pasha Tatashin pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- include/linux/kexec_handover.h | 28 +----- kernel/kexec_handover.c | 164 +++++++++++++++++-------------- kernel/kexec_handover_debugfs.c | 17 ++-- kernel/kexec_handover_internal.h | 5 +- lib/test_kho.c | 30 +----- mm/memblock.c | 62 +++--------- 6 files changed, 127 insertions(+), 179 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 04d0108db98e..2faf290803ce 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -10,14 +10,7 @@ struct kho_scratch { phys_addr_t size; };
-/* KHO Notifier index */ -enum kho_event { - KEXEC_KHO_FINALIZE = 0, - KEXEC_KHO_ABORT = 1, -}; - struct folio; -struct notifier_block; struct page;
#define DECLARE_KHOSER_PTR(name, type) \ @@ -37,8 +30,6 @@ struct page; (typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \ })
-struct kho_serialization; - struct kho_vmalloc_chunk; struct kho_vmalloc { DECLARE_KHOSER_PTR(first, struct kho_vmalloc_chunk *); @@ -57,12 +48,10 @@ int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); struct folio *kho_restore_folio(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages); void *kho_restore_vmalloc(const struct kho_vmalloc *preservation); -int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt); +int kho_add_subtree(const char *name, void *fdt); +void kho_remove_subtree(void *fdt); int kho_retrieve_subtree(const char *name, phys_addr_t *phys);
-int register_kho_notifier(struct notifier_block *nb); -int unregister_kho_notifier(struct notifier_block *nb); - void kho_memory_init(void);
void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, @@ -114,23 +103,16 @@ static inline void *kho_restore_vmalloc(const struct kho_vmalloc *preservation) return NULL; }
-static inline int kho_add_subtree(struct kho_serialization *ser, - const char *name, void *fdt) +static inline int kho_add_subtree(const char *name, void *fdt) { return -EOPNOTSUPP; }
-static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys) +static inline void kho_remove_subtree(void *fdt) { - return -EOPNOTSUPP; }
-static inline int register_kho_notifier(struct notifier_block *nb) -{ - return -EOPNOTSUPP; -} - -static inline int unregister_kho_notifier(struct notifier_block *nb) +static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys) { return -EOPNOTSUPP; } diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index da071277d85e..0a4234269fe5 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -16,7 +16,6 @@ #include <linux/libfdt.h> #include <linux/list.h> #include <linux/memblock.h> -#include <linux/notifier.h> #include <linux/page-isolation.h> #include <linux/vmalloc.h>
@@ -103,29 +102,34 @@ struct kho_mem_track {
struct khoser_mem_chunk;
-struct kho_serialization { - struct page *fdt; - struct kho_mem_track track; - /* First chunk of serialized preserved memory map */ - struct khoser_mem_chunk *preserved_mem_map; +struct kho_sub_fdt { + struct list_head l; + const char *name; + void *fdt; };
struct kho_out { - struct blocking_notifier_head chain_head; - struct mutex lock; /* protects KHO FDT finalization */ - struct kho_serialization ser; + void *fdt; bool finalized; + struct mutex lock; /* protects KHO FDT finalization */ + + struct list_head sub_fdts; + struct mutex fdts_lock; + + struct kho_mem_track track; + /* First chunk of serialized preserved memory map */ + struct khoser_mem_chunk *preserved_mem_map; + struct kho_debugfs dbg; };
static struct kho_out kho_out = { - .chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head), .lock = __MUTEX_INITIALIZER(kho_out.lock), - .ser = { - .track = { - .orders = XARRAY_INIT(kho_out.ser.track.orders, 0), - }, + .track = { + .orders = XARRAY_INIT(kho_out.track.orders, 0), }, + .sub_fdts = LIST_HEAD_INIT(kho_out.sub_fdts), + .fdts_lock = __MUTEX_INITIALIZER(kho_out.fdts_lock), .finalized = false, };
@@ -369,7 +373,7 @@ static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk) } }
-static int kho_mem_serialize(struct kho_serialization *ser) +static int kho_mem_serialize(struct kho_out *kho_out) { struct khoser_mem_chunk *first_chunk = NULL; struct khoser_mem_chunk *chunk = NULL; @@ -377,7 +381,7 @@ static int kho_mem_serialize(struct kho_serialization *ser) unsigned long order; int err = -ENOMEM;
- xa_for_each(&ser->track.orders, order, physxa) { + xa_for_each(&kho_out->track.orders, order, physxa) { struct kho_mem_phys_bits *bits; unsigned long phys;
@@ -409,7 +413,7 @@ static int kho_mem_serialize(struct kho_serialization *ser) } }
- ser->preserved_mem_map = first_chunk; + kho_out->preserved_mem_map = first_chunk;
return 0;
@@ -670,7 +674,6 @@ static void __init kho_reserve_scratch(void)
/** * kho_add_subtree - record the physical address of a sub FDT in KHO root tree. - * @ser: serialization control object passed by KHO notifiers. * @name: name of the sub tree. * @fdt: the sub tree blob. * @@ -684,34 +687,45 @@ static void __init kho_reserve_scratch(void) * * Return: 0 on success, error code on failure */ -int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) { - int err = 0; - u64 phys = (u64)virt_to_phys(fdt); - void *root = page_to_virt(ser->fdt); + struct kho_sub_fdt *sub_fdt; + int err;
- err |= fdt_begin_node(root, name); - err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys)); - err |= fdt_end_node(root); + sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL); + if (!sub_fdt) + return -ENOMEM;
- if (err) - return err; + INIT_LIST_HEAD(&sub_fdt->l); + sub_fdt->name = name; + sub_fdt->fdt = fdt;
- return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false); + mutex_lock(&kho_out.fdts_lock); + list_add_tail(&sub_fdt->l, &kho_out.sub_fdts); + err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false); + mutex_unlock(&kho_out.fdts_lock); + + return err; } EXPORT_SYMBOL_GPL(kho_add_subtree);
-int register_kho_notifier(struct notifier_block *nb) +void kho_remove_subtree(void *fdt) { - return blocking_notifier_chain_register(&kho_out.chain_head, nb); -} -EXPORT_SYMBOL_GPL(register_kho_notifier); + struct kho_sub_fdt *sub_fdt; + + mutex_lock(&kho_out.fdts_lock); + list_for_each_entry(sub_fdt, &kho_out.sub_fdts, l) { + if (sub_fdt->fdt == fdt) { + list_del(&sub_fdt->l); + kfree(sub_fdt); + kho_debugfs_fdt_remove(&kho_out.dbg, fdt); + break; + } + } + mutex_unlock(&kho_out.fdts_lock);
-int unregister_kho_notifier(struct notifier_block *nb) -{ - return blocking_notifier_chain_unregister(&kho_out.chain_head, nb); } -EXPORT_SYMBOL_GPL(unregister_kho_notifier); +EXPORT_SYMBOL_GPL(kho_remove_subtree);
/** * kho_preserve_folio - preserve a folio across kexec. @@ -726,7 +740,7 @@ int kho_preserve_folio(struct folio *folio) { const unsigned long pfn = folio_pfn(folio); const unsigned int order = folio_order(folio); - struct kho_mem_track *track = &kho_out.ser.track; + struct kho_mem_track *track = &kho_out.track;
if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order))) return -EINVAL; @@ -747,7 +761,7 @@ EXPORT_SYMBOL_GPL(kho_preserve_folio); */ int kho_preserve_pages(struct page *page, unsigned int nr_pages) { - struct kho_mem_track *track = &kho_out.ser.track; + struct kho_mem_track *track = &kho_out.track; const unsigned long start_pfn = page_to_pfn(page); const unsigned long end_pfn = start_pfn + nr_pages; unsigned long pfn = start_pfn; @@ -848,7 +862,7 @@ static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur
static void kho_vmalloc_unpreserve_chunk(struct kho_vmalloc_chunk *chunk) { - struct kho_mem_track *track = &kho_out.ser.track; + struct kho_mem_track *track = &kho_out.track; unsigned long pfn = PHYS_PFN(virt_to_phys(chunk));
__kho_unpreserve(track, pfn, pfn + 1); @@ -1030,11 +1044,11 @@ EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
static int __kho_abort(void) { - int err; + int err = 0; unsigned long order; struct kho_mem_phys *physxa;
- xa_for_each(&kho_out.ser.track.orders, order, physxa) { + xa_for_each(&kho_out.track.orders, order, physxa) { struct kho_mem_phys_bits *bits; unsigned long phys;
@@ -1044,17 +1058,13 @@ static int __kho_abort(void) xa_destroy(&physxa->phys_bits); kfree(physxa); } - xa_destroy(&kho_out.ser.track.orders); + xa_destroy(&kho_out.track.orders);
- if (kho_out.ser.preserved_mem_map) { - kho_mem_ser_free(kho_out.ser.preserved_mem_map); - kho_out.ser.preserved_mem_map = NULL; + if (kho_out.preserved_mem_map) { + kho_mem_ser_free(kho_out.preserved_mem_map); + kho_out.preserved_mem_map = NULL; }
- err = blocking_notifier_call_chain(&kho_out.chain_head, KEXEC_KHO_ABORT, - NULL); - err = notifier_to_errno(err); - if (err) pr_err("Failed to abort KHO finalization: %d\n", err);
@@ -1077,7 +1087,8 @@ int kho_abort(void) return ret;
kho_out.finalized = false; - kho_debugfs_cleanup(&kho_out.dbg); + + kho_debugfs_fdt_remove(&kho_out.dbg, kho_out.fdt);
return 0; } @@ -1086,41 +1097,46 @@ static int __kho_finalize(void) { int err = 0; u64 *preserved_mem_map; - void *fdt = page_to_virt(kho_out.ser.fdt); + void *root = kho_out.fdt; + struct kho_sub_fdt *fdt;
- err |= fdt_create(fdt, PAGE_SIZE); - err |= fdt_finish_reservemap(fdt); - err |= fdt_begin_node(fdt, ""); - err |= fdt_property_string(fdt, "compatible", KHO_FDT_COMPATIBLE); + err |= fdt_create(root, PAGE_SIZE); + err |= fdt_finish_reservemap(root); + err |= fdt_begin_node(root, ""); + err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE); /** * Reserve the preserved-memory-map property in the root FDT, so * that all property definitions will precede subnodes created by * KHO callers. */ - err |= fdt_property_placeholder(fdt, PROP_PRESERVED_MEMORY_MAP, + err |= fdt_property_placeholder(root, PROP_PRESERVED_MEMORY_MAP, sizeof(*preserved_mem_map), (void **)&preserved_mem_map); if (err) goto abort;
- err = kho_preserve_folio(page_folio(kho_out.ser.fdt)); + err = kho_preserve_folio(virt_to_folio(kho_out.fdt)); if (err) goto abort;
- err = blocking_notifier_call_chain(&kho_out.chain_head, - KEXEC_KHO_FINALIZE, &kho_out.ser); - err = notifier_to_errno(err); + err = kho_mem_serialize(&kho_out); if (err) goto abort;
- err = kho_mem_serialize(&kho_out.ser); - if (err) - goto abort; + *preserved_mem_map = (u64)virt_to_phys(kho_out.preserved_mem_map); + + mutex_lock(&kho_out.fdts_lock); + list_for_each_entry(fdt, &kho_out.sub_fdts, l) { + phys_addr_t phys = virt_to_phys(fdt->fdt);
- *preserved_mem_map = (u64)virt_to_phys(kho_out.ser.preserved_mem_map); + err |= fdt_begin_node(root, fdt->name); + err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys)); + err |= fdt_end_node(root); + } + mutex_unlock(&kho_out.fdts_lock);
- err |= fdt_end_node(fdt); - err |= fdt_finish(fdt); + err |= fdt_end_node(root); + err |= fdt_finish(root);
abort: if (err) { @@ -1149,7 +1165,7 @@ int kho_finalize(void) kho_out.finalized = true;
return kho_debugfs_fdt_add(&kho_out.dbg, "fdt", - page_to_virt(kho_out.ser.fdt), true); + kho_out.fdt, true); }
bool kho_finalized(void) @@ -1232,15 +1248,17 @@ static __init int kho_init(void) { int err = 0; const void *fdt = kho_get_fdt(); + struct page *fdt_page;
if (!kho_enable) return 0;
- kho_out.ser.fdt = alloc_page(GFP_KERNEL); - if (!kho_out.ser.fdt) { + fdt_page = alloc_page(GFP_KERNEL); + if (!fdt_page) { err = -ENOMEM; goto err_free_scratch; } + kho_out.fdt = page_to_virt(fdt_page);
err = kho_debugfs_init(); if (err) @@ -1268,8 +1286,8 @@ static __init int kho_init(void) return 0;
err_free_fdt: - put_page(kho_out.ser.fdt); - kho_out.ser.fdt = NULL; + put_page(fdt_page); + kho_out.fdt = NULL; err_free_scratch: for (int i = 0; i < kho_scratch_cnt; i++) { void *start = __va(kho_scratch[i].addr); @@ -1280,7 +1298,7 @@ static __init int kho_init(void) kho_enable = false; return err; } -late_initcall(kho_init); +fs_initcall(kho_init);
static void __init kho_release_scratch(void) { @@ -1416,7 +1434,7 @@ int kho_fill_kimage(struct kimage *image) if (!kho_out.finalized) return 0;
- image->kho.fdt = page_to_phys(kho_out.ser.fdt); + image->kho.fdt = virt_to_phys(kho_out.fdt);
scratch_size = sizeof(*kho_scratch) * kho_scratch_cnt; scratch = (struct kexec_buf){ diff --git a/kernel/kexec_handover_debugfs.c b/kernel/kexec_handover_debugfs.c index a91b279f1b23..46e9e6c0791f 100644 --- a/kernel/kexec_handover_debugfs.c +++ b/kernel/kexec_handover_debugfs.c @@ -61,14 +61,17 @@ int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt); }
-void kho_debugfs_cleanup(struct kho_debugfs *dbg) +void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt) { - struct fdt_debugfs *ff, *tmp; - - list_for_each_entry_safe(ff, tmp, &dbg->fdt_list, list) { - debugfs_remove(ff->file); - list_del(&ff->list); - kfree(ff); + struct fdt_debugfs *ff; + + list_for_each_entry(ff, &dbg->fdt_list, list) { + if (ff->wrapper.data == fdt) { + debugfs_remove(ff->file); + list_del(&ff->list); + kfree(ff); + break; + } } }
diff --git a/kernel/kexec_handover_internal.h b/kernel/kexec_handover_internal.h index 28c0e971613d..17ae101dc6ae 100644 --- a/kernel/kexec_handover_internal.h +++ b/kernel/kexec_handover_internal.h @@ -30,7 +30,7 @@ void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt); int kho_out_debugfs_init(struct kho_debugfs *dbg); int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, const void *fdt, bool root); -void kho_debugfs_cleanup(struct kho_debugfs *dbg); +void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt); #else static inline int kho_debugfs_init(void) { return 0; } static inline void kho_in_debugfs_init(struct kho_debugfs *dbg, @@ -38,7 +38,8 @@ static inline void kho_in_debugfs_init(struct kho_debugfs *dbg, static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; } static inline int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, const void *fdt, bool root) { return 0; } -static inline void kho_debugfs_cleanup(struct kho_debugfs *dbg) {} +static inline void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, + void *fdt) { } #endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */
#ifdef CONFIG_KEXEC_HANDOVER_DEBUG diff --git a/lib/test_kho.c b/lib/test_kho.c index 60cd899ea745..8d57049e8c8c 100644 --- a/lib/test_kho.c +++ b/lib/test_kho.c @@ -39,33 +39,17 @@ struct kho_test_state {
static struct kho_test_state kho_test_state;
-static int kho_test_notifier(struct notifier_block *self, unsigned long cmd, - void *v) +static int kho_test(void) { struct kho_test_state *state = &kho_test_state; - struct kho_serialization *ser = v; int err = 0;
- switch (cmd) { - case KEXEC_KHO_ABORT: - return NOTIFY_DONE; - case KEXEC_KHO_FINALIZE: - /* Handled below */ - break; - default: - return NOTIFY_BAD; - } - err |= kho_preserve_folio(state->fdt); - err |= kho_add_subtree(ser, KHO_TEST_FDT, folio_address(state->fdt)); + err |= kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));
return err ? NOTIFY_BAD : NOTIFY_DONE; }
-static struct notifier_block kho_test_nb = { - .notifier_call = kho_test_notifier, -}; - static int kho_test_save_data(struct kho_test_state *state, void *fdt) { phys_addr_t *folios_info __free(kvfree) = NULL; @@ -102,6 +86,9 @@ static int kho_test_save_data(struct kho_test_state *state, void *fdt) if (!err) state->folios_info = no_free_ptr(folios_info);
+ if (!err) + err = kho_test(); + return err; }
@@ -203,14 +190,8 @@ static int kho_test_save(void) if (err) goto err_free_folios;
- err = register_kho_notifier(&kho_test_nb); - if (err) - goto err_free_fdt; - return 0;
-err_free_fdt: - folio_put(state->fdt); err_free_folios: kvfree(folios); return err; @@ -326,7 +307,6 @@ static void kho_test_cleanup(void)
static void __exit kho_test_exit(void) { - unregister_kho_notifier(&kho_test_nb); kho_test_cleanup(); } module_exit(kho_test_exit); diff --git a/mm/memblock.c b/mm/memblock.c index e23e16618e9b..e3bef9b35d63 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -2444,53 +2444,18 @@ int reserve_mem_release_by_name(const char *name) #define MEMBLOCK_KHO_FDT "memblock" #define MEMBLOCK_KHO_NODE_COMPATIBLE "memblock-v1" #define RESERVE_MEM_KHO_NODE_COMPATIBLE "reserve-mem-v1" -static struct page *kho_fdt; - -static int reserve_mem_kho_finalize(struct kho_serialization *ser) -{ - int err = 0, i; - - for (i = 0; i < reserved_mem_count; i++) { - struct reserve_mem_table *map = &reserved_mem_table[i]; - struct page *page = phys_to_page(map->start); - unsigned int nr_pages = map->size >> PAGE_SHIFT; - - err |= kho_preserve_pages(page, nr_pages); - } - - err |= kho_preserve_folio(page_folio(kho_fdt)); - err |= kho_add_subtree(ser, MEMBLOCK_KHO_FDT, page_to_virt(kho_fdt)); - - return notifier_from_errno(err); -} - -static int reserve_mem_kho_notifier(struct notifier_block *self, - unsigned long cmd, void *v) -{ - switch (cmd) { - case KEXEC_KHO_FINALIZE: - return reserve_mem_kho_finalize((struct kho_serialization *)v); - case KEXEC_KHO_ABORT: - return NOTIFY_DONE; - default: - return NOTIFY_BAD; - } -} - -static struct notifier_block reserve_mem_kho_nb = { - .notifier_call = reserve_mem_kho_notifier, -};
static int __init prepare_kho_fdt(void) { int err = 0, i; + struct page *fdt_page; void *fdt;
- kho_fdt = alloc_page(GFP_KERNEL); - if (!kho_fdt) + fdt_page = alloc_page(GFP_KERNEL); + if (!fdt_page) return -ENOMEM;
- fdt = page_to_virt(kho_fdt); + fdt = page_to_virt(fdt_page);
err |= fdt_create(fdt, PAGE_SIZE); err |= fdt_finish_reservemap(fdt); @@ -2499,7 +2464,10 @@ static int __init prepare_kho_fdt(void) err |= fdt_property_string(fdt, "compatible", MEMBLOCK_KHO_NODE_COMPATIBLE); for (i = 0; i < reserved_mem_count; i++) { struct reserve_mem_table *map = &reserved_mem_table[i]; + struct page *page = phys_to_page(map->start); + unsigned int nr_pages = map->size >> PAGE_SHIFT;
+ err |= kho_preserve_pages(page, nr_pages); err |= fdt_begin_node(fdt, map->name); err |= fdt_property_string(fdt, "compatible", RESERVE_MEM_KHO_NODE_COMPATIBLE); err |= fdt_property(fdt, "start", &map->start, sizeof(map->start)); @@ -2507,13 +2475,16 @@ static int __init prepare_kho_fdt(void) err |= fdt_end_node(fdt); } err |= fdt_end_node(fdt); - err |= fdt_finish(fdt);
+ err |= kho_preserve_folio(page_folio(fdt_page)); + + if (!err) + err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt); + if (err) { pr_err("failed to prepare memblock FDT for KHO: %d\n", err); - put_page(kho_fdt); - kho_fdt = NULL; + put_page(fdt_page); }
return err; @@ -2529,13 +2500,6 @@ static int __init reserve_mem_init(void) err = prepare_kho_fdt(); if (err) return err; - - err = register_kho_notifier(&reserve_mem_kho_nb); - if (err) { - put_page(kho_fdt); - kho_fdt = NULL; - } - return err; } late_initcall(reserve_mem_init);
Hi Pasha,
On Tue, Oct 21 2025, Pasha Tatashin wrote:
From: "Mike Rapoport (Microsoft)" rppt@kernel.org
The KHO framework uses a notifier chain as the mechanism for clients to participate in the finalization process. While this works for a single, central state machine, it is too restrictive for kernel-internal components like pstore/reserve_mem or IMA. These components need a simpler, direct way to register their state for preservation (e.g., during their initcall) without being part of a complex, shutdown-time notifier sequence. The notifier model forces all participants into a single finalization flow and makes direct preservation from an arbitrary context difficult. This patch refactors the client participation model by removing the notifier chain and introducing a direct API for managing FDT subtrees.
The core kho_finalize() and kho_abort() state machine remains, but clients now register their data with KHO beforehand.
Signed-off-by: Mike Rapoport (Microsoft) rppt@kernel.org Co-developed-by: Pasha Tatashin pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
include/linux/kexec_handover.h | 28 +----- kernel/kexec_handover.c | 164 +++++++++++++++++-------------- kernel/kexec_handover_debugfs.c | 17 ++-- kernel/kexec_handover_internal.h | 5 +- lib/test_kho.c | 30 +----- mm/memblock.c | 62 +++--------- 6 files changed, 127 insertions(+), 179 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 04d0108db98e..2faf290803ce 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -10,14 +10,7 @@ struct kho_scratch { phys_addr_t size; }; -/* KHO Notifier index */ -enum kho_event {
- KEXEC_KHO_FINALIZE = 0,
- KEXEC_KHO_ABORT = 1,
-};
struct folio; -struct notifier_block; struct page; #define DECLARE_KHOSER_PTR(name, type) \ @@ -37,8 +30,6 @@ struct page; (typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \ }) -struct kho_serialization;
struct kho_vmalloc_chunk; struct kho_vmalloc { DECLARE_KHOSER_PTR(first, struct kho_vmalloc_chunk *); @@ -57,12 +48,10 @@ int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); struct folio *kho_restore_folio(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages); void *kho_restore_vmalloc(const struct kho_vmalloc *preservation); -int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt); +int kho_add_subtree(const char *name, void *fdt); +void kho_remove_subtree(void *fdt); int kho_retrieve_subtree(const char *name, phys_addr_t *phys); -int register_kho_notifier(struct notifier_block *nb); -int unregister_kho_notifier(struct notifier_block *nb);
void kho_memory_init(void); void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys, @@ -114,23 +103,16 @@ static inline void *kho_restore_vmalloc(const struct kho_vmalloc *preservation) return NULL; } -static inline int kho_add_subtree(struct kho_serialization *ser,
const char *name, void *fdt)+static inline int kho_add_subtree(const char *name, void *fdt) { return -EOPNOTSUPP; } -static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys) +static inline void kho_remove_subtree(void *fdt) {
- return -EOPNOTSUPP;
} -static inline int register_kho_notifier(struct notifier_block *nb) -{
- return -EOPNOTSUPP;
-}
-static inline int unregister_kho_notifier(struct notifier_block *nb) +static inline int kho_retrieve_subtree(const char *name, phys_addr_t *phys) { return -EOPNOTSUPP; } diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index da071277d85e..0a4234269fe5 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -16,7 +16,6 @@ #include <linux/libfdt.h> #include <linux/list.h> #include <linux/memblock.h> -#include <linux/notifier.h> #include <linux/page-isolation.h> #include <linux/vmalloc.h> @@ -103,29 +102,34 @@ struct kho_mem_track { struct khoser_mem_chunk; -struct kho_serialization {
- struct page *fdt;
- struct kho_mem_track track;
- /* First chunk of serialized preserved memory map */
- struct khoser_mem_chunk *preserved_mem_map;
+struct kho_sub_fdt {
- struct list_head l;
- const char *name;
- void *fdt;
}; struct kho_out {
- struct blocking_notifier_head chain_head;
- struct mutex lock; /* protects KHO FDT finalization */
- struct kho_serialization ser;
- void *fdt; bool finalized;
- struct mutex lock; /* protects KHO FDT finalization */
- struct list_head sub_fdts;
- struct mutex fdts_lock;
- struct kho_mem_track track;
- /* First chunk of serialized preserved memory map */
- struct khoser_mem_chunk *preserved_mem_map;
- struct kho_debugfs dbg;
}; static struct kho_out kho_out = {
- .chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head), .lock = __MUTEX_INITIALIZER(kho_out.lock),
- .ser = {
.track = {.orders = XARRAY_INIT(kho_out.ser.track.orders, 0),},
- .track = {
.orders = XARRAY_INIT(kho_out.track.orders, 0),- .sub_fdts = LIST_HEAD_INIT(kho_out.sub_fdts),
- .fdts_lock = __MUTEX_INITIALIZER(kho_out.fdts_lock), .finalized = false,
}; @@ -369,7 +373,7 @@ static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk) } } -static int kho_mem_serialize(struct kho_serialization *ser) +static int kho_mem_serialize(struct kho_out *kho_out) { struct khoser_mem_chunk *first_chunk = NULL; struct khoser_mem_chunk *chunk = NULL; @@ -377,7 +381,7 @@ static int kho_mem_serialize(struct kho_serialization *ser) unsigned long order; int err = -ENOMEM;
- xa_for_each(&ser->track.orders, order, physxa) {
- xa_for_each(&kho_out->track.orders, order, physxa) { struct kho_mem_phys_bits *bits; unsigned long phys;
@@ -409,7 +413,7 @@ static int kho_mem_serialize(struct kho_serialization *ser) } }
- ser->preserved_mem_map = first_chunk;
- kho_out->preserved_mem_map = first_chunk;
return 0; @@ -670,7 +674,6 @@ static void __init kho_reserve_scratch(void) /**
- kho_add_subtree - record the physical address of a sub FDT in KHO root tree.
- @ser: serialization control object passed by KHO notifiers.
- @name: name of the sub tree.
- @fdt: the sub tree blob.
@@ -684,34 +687,45 @@ static void __init kho_reserve_scratch(void)
- Return: 0 on success, error code on failure
*/ -int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
- int err = 0;
- u64 phys = (u64)virt_to_phys(fdt);
- void *root = page_to_virt(ser->fdt);
- struct kho_sub_fdt *sub_fdt;
- int err;
- err |= fdt_begin_node(root, name);
- err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));
- err |= fdt_end_node(root);
- sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);
- if (!sub_fdt)
return -ENOMEM;
- if (err)
return err;
- INIT_LIST_HEAD(&sub_fdt->l);
- sub_fdt->name = name;
- sub_fdt->fdt = fdt;
- return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
- mutex_lock(&kho_out.fdts_lock);
- list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);
- err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
- mutex_unlock(&kho_out.fdts_lock);
- return err;
} EXPORT_SYMBOL_GPL(kho_add_subtree); -int register_kho_notifier(struct notifier_block *nb) +void kho_remove_subtree(void *fdt) {
- return blocking_notifier_chain_register(&kho_out.chain_head, nb);
-} -EXPORT_SYMBOL_GPL(register_kho_notifier);
- struct kho_sub_fdt *sub_fdt;
- mutex_lock(&kho_out.fdts_lock);
- list_for_each_entry(sub_fdt, &kho_out.sub_fdts, l) {
list_for_each_entry_safe() here since we delete.
if (sub_fdt->fdt == fdt) {list_del(&sub_fdt->l);kfree(sub_fdt);kho_debugfs_fdt_remove(&kho_out.dbg, fdt);break;}- }
- mutex_unlock(&kho_out.fdts_lock);
-int unregister_kho_notifier(struct notifier_block *nb) -{
- return blocking_notifier_chain_unregister(&kho_out.chain_head, nb);
} -EXPORT_SYMBOL_GPL(unregister_kho_notifier); +EXPORT_SYMBOL_GPL(kho_remove_subtree); /**
- kho_preserve_folio - preserve a folio across kexec.
@@ -726,7 +740,7 @@ int kho_preserve_folio(struct folio *folio) { const unsigned long pfn = folio_pfn(folio); const unsigned int order = folio_order(folio);
- struct kho_mem_track *track = &kho_out.ser.track;
- struct kho_mem_track *track = &kho_out.track;
if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order))) return -EINVAL; @@ -747,7 +761,7 @@ EXPORT_SYMBOL_GPL(kho_preserve_folio); */ int kho_preserve_pages(struct page *page, unsigned int nr_pages) {
- struct kho_mem_track *track = &kho_out.ser.track;
- struct kho_mem_track *track = &kho_out.track; const unsigned long start_pfn = page_to_pfn(page); const unsigned long end_pfn = start_pfn + nr_pages; unsigned long pfn = start_pfn;
@@ -848,7 +862,7 @@ static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur static void kho_vmalloc_unpreserve_chunk(struct kho_vmalloc_chunk *chunk) {
- struct kho_mem_track *track = &kho_out.ser.track;
- struct kho_mem_track *track = &kho_out.track; unsigned long pfn = PHYS_PFN(virt_to_phys(chunk));
__kho_unpreserve(track, pfn, pfn + 1); @@ -1030,11 +1044,11 @@ EXPORT_SYMBOL_GPL(kho_restore_vmalloc); static int __kho_abort(void) {
- int err;
- int err = 0; unsigned long order; struct kho_mem_phys *physxa;
- xa_for_each(&kho_out.ser.track.orders, order, physxa) {
- xa_for_each(&kho_out.track.orders, order, physxa) { struct kho_mem_phys_bits *bits; unsigned long phys;
@@ -1044,17 +1058,13 @@ static int __kho_abort(void) xa_destroy(&physxa->phys_bits); kfree(physxa); }
- xa_destroy(&kho_out.ser.track.orders);
- xa_destroy(&kho_out.track.orders);
- if (kho_out.ser.preserved_mem_map) {
kho_mem_ser_free(kho_out.ser.preserved_mem_map);kho_out.ser.preserved_mem_map = NULL;
- if (kho_out.preserved_mem_map) {
kho_mem_ser_free(kho_out.preserved_mem_map);kho_out.preserved_mem_map = NULL;
- err = blocking_notifier_call_chain(&kho_out.chain_head, KEXEC_KHO_ABORT,
NULL);- err = notifier_to_errno(err);
- if (err) pr_err("Failed to abort KHO finalization: %d\n", err);
@@ -1077,7 +1087,8 @@ int kho_abort(void) return ret; kho_out.finalized = false;
- kho_debugfs_cleanup(&kho_out.dbg);
- kho_debugfs_fdt_remove(&kho_out.dbg, kho_out.fdt);
return 0; } @@ -1086,41 +1097,46 @@ static int __kho_finalize(void) { int err = 0; u64 *preserved_mem_map;
- void *fdt = page_to_virt(kho_out.ser.fdt);
- void *root = kho_out.fdt;
- struct kho_sub_fdt *fdt;
- err |= fdt_create(fdt, PAGE_SIZE);
- err |= fdt_finish_reservemap(fdt);
- err |= fdt_begin_node(fdt, "");
- err |= fdt_property_string(fdt, "compatible", KHO_FDT_COMPATIBLE);
- err |= fdt_create(root, PAGE_SIZE);
- err |= fdt_finish_reservemap(root);
- err |= fdt_begin_node(root, "");
- err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE); /**
*/
- Reserve the preserved-memory-map property in the root FDT, so
- that all property definitions will precede subnodes created by
- KHO callers.
- err |= fdt_property_placeholder(fdt, PROP_PRESERVED_MEMORY_MAP,
- err |= fdt_property_placeholder(root, PROP_PRESERVED_MEMORY_MAP, sizeof(*preserved_mem_map), (void **)&preserved_mem_map); if (err) goto abort;
- err = kho_preserve_folio(page_folio(kho_out.ser.fdt));
- err = kho_preserve_folio(virt_to_folio(kho_out.fdt)); if (err) goto abort;
- err = blocking_notifier_call_chain(&kho_out.chain_head,
KEXEC_KHO_FINALIZE, &kho_out.ser);- err = notifier_to_errno(err);
- err = kho_mem_serialize(&kho_out); if (err) goto abort;
- err = kho_mem_serialize(&kho_out.ser);
- if (err)
goto abort;
- *preserved_mem_map = (u64)virt_to_phys(kho_out.preserved_mem_map);
- mutex_lock(&kho_out.fdts_lock);
- list_for_each_entry(fdt, &kho_out.sub_fdts, l) {
phys_addr_t phys = virt_to_phys(fdt->fdt);
- *preserved_mem_map = (u64)virt_to_phys(kho_out.ser.preserved_mem_map);
err |= fdt_begin_node(root, fdt->name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);- }
- mutex_unlock(&kho_out.fdts_lock);
- err |= fdt_end_node(fdt);
- err |= fdt_finish(fdt);
- err |= fdt_end_node(root);
- err |= fdt_finish(root);
abort: if (err) { @@ -1149,7 +1165,7 @@ int kho_finalize(void) kho_out.finalized = true; return kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
page_to_virt(kho_out.ser.fdt), true);
kho_out.fdt, true);} bool kho_finalized(void) @@ -1232,15 +1248,17 @@ static __init int kho_init(void) { int err = 0; const void *fdt = kho_get_fdt();
- struct page *fdt_page;
if (!kho_enable) return 0;
- kho_out.ser.fdt = alloc_page(GFP_KERNEL);
- if (!kho_out.ser.fdt) {
- fdt_page = alloc_page(GFP_KERNEL);
- if (!fdt_page) { err = -ENOMEM; goto err_free_scratch; }
- kho_out.fdt = page_to_virt(fdt_page);
err = kho_debugfs_init(); if (err) @@ -1268,8 +1286,8 @@ static __init int kho_init(void) return 0; err_free_fdt:
- put_page(kho_out.ser.fdt);
- kho_out.ser.fdt = NULL;
- put_page(fdt_page);
- kho_out.fdt = NULL;
err_free_scratch: for (int i = 0; i < kho_scratch_cnt; i++) { void *start = __va(kho_scratch[i].addr); @@ -1280,7 +1298,7 @@ static __init int kho_init(void) kho_enable = false; return err; } -late_initcall(kho_init); +fs_initcall(kho_init);
Is this change related to this patch? Also, why fs_initcall?
static void __init kho_release_scratch(void) { @@ -1416,7 +1434,7 @@ int kho_fill_kimage(struct kimage *image) if (!kho_out.finalized) return 0;
- image->kho.fdt = page_to_phys(kho_out.ser.fdt);
- image->kho.fdt = virt_to_phys(kho_out.fdt);
scratch_size = sizeof(*kho_scratch) * kho_scratch_cnt; scratch = (struct kexec_buf){ diff --git a/kernel/kexec_handover_debugfs.c b/kernel/kexec_handover_debugfs.c index a91b279f1b23..46e9e6c0791f 100644 --- a/kernel/kexec_handover_debugfs.c +++ b/kernel/kexec_handover_debugfs.c @@ -61,14 +61,17 @@ int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt); } -void kho_debugfs_cleanup(struct kho_debugfs *dbg) +void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt) {
- struct fdt_debugfs *ff, *tmp;
- list_for_each_entry_safe(ff, tmp, &dbg->fdt_list, list) {
debugfs_remove(ff->file);list_del(&ff->list);kfree(ff);
- struct fdt_debugfs *ff;
- list_for_each_entry(ff, &dbg->fdt_list, list) {
list_for_each_entry_safe() here too.
if (ff->wrapper.data == fdt) {debugfs_remove(ff->file);list_del(&ff->list);kfree(ff);break;}} diff --git a/kernel/kexec_handover_internal.h b/kernel/kexec_handover_internal.h index 28c0e971613d..17ae101dc6ae 100644 --- a/kernel/kexec_handover_internal.h +++ b/kernel/kexec_handover_internal.h @@ -30,7 +30,7 @@ void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt); int kho_out_debugfs_init(struct kho_debugfs *dbg); int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, const void *fdt, bool root); -void kho_debugfs_cleanup(struct kho_debugfs *dbg); +void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt); #else static inline int kho_debugfs_init(void) { return 0; } static inline void kho_in_debugfs_init(struct kho_debugfs *dbg, @@ -38,7 +38,8 @@ static inline void kho_in_debugfs_init(struct kho_debugfs *dbg, static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; } static inline int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, const void *fdt, bool root) { return 0; } -static inline void kho_debugfs_cleanup(struct kho_debugfs *dbg) {} +static inline void kho_debugfs_fdt_remove(struct kho_debugfs *dbg,
void *fdt) { }#endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */ #ifdef CONFIG_KEXEC_HANDOVER_DEBUG diff --git a/lib/test_kho.c b/lib/test_kho.c index 60cd899ea745..8d57049e8c8c 100644 --- a/lib/test_kho.c +++ b/lib/test_kho.c @@ -39,33 +39,17 @@ struct kho_test_state { static struct kho_test_state kho_test_state; -static int kho_test_notifier(struct notifier_block *self, unsigned long cmd,
void *v)+static int kho_test(void) { struct kho_test_state *state = &kho_test_state;
- struct kho_serialization *ser = v; int err = 0;
- switch (cmd) {
- case KEXEC_KHO_ABORT:
return NOTIFY_DONE;- case KEXEC_KHO_FINALIZE:
/* Handled below */break;- default:
return NOTIFY_BAD;- }
- err |= kho_preserve_folio(state->fdt);
- err |= kho_add_subtree(ser, KHO_TEST_FDT, folio_address(state->fdt));
- err |= kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));
return err ? NOTIFY_BAD : NOTIFY_DONE; } -static struct notifier_block kho_test_nb = {
- .notifier_call = kho_test_notifier,
-};
static int kho_test_save_data(struct kho_test_state *state, void *fdt) { phys_addr_t *folios_info __free(kvfree) = NULL; @@ -102,6 +86,9 @@ static int kho_test_save_data(struct kho_test_state *state, void *fdt) if (!err) state->folios_info = no_free_ptr(folios_info);
- if (!err)
err = kho_test();
This name is very undescriptive. Also, not the right place to add the subtree since the FDT isn't finished yet. I think it should be done from kho_test_save() instead. This patch is also missing removing the subtree at exit, and that can cause a UAF.
I sent you a patch earlier with my take on how it should be done. I still think that is the way to go: https://lore.kernel.org/all/mafs0347woui2.fsf@kernel.org/
- return err;
} @@ -203,14 +190,8 @@ static int kho_test_save(void) if (err) goto err_free_folios;
- err = register_kho_notifier(&kho_test_nb);
- if (err)
goto err_free_fdt;- return 0;
-err_free_fdt:
- folio_put(state->fdt);
err_free_folios: kvfree(folios); return err; @@ -326,7 +307,6 @@ static void kho_test_cleanup(void) static void __exit kho_test_exit(void) {
- unregister_kho_notifier(&kho_test_nb); kho_test_cleanup();
} module_exit(kho_test_exit); diff --git a/mm/memblock.c b/mm/memblock.c index e23e16618e9b..e3bef9b35d63 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -2444,53 +2444,18 @@ int reserve_mem_release_by_name(const char *name) #define MEMBLOCK_KHO_FDT "memblock" #define MEMBLOCK_KHO_NODE_COMPATIBLE "memblock-v1" #define RESERVE_MEM_KHO_NODE_COMPATIBLE "reserve-mem-v1" -static struct page *kho_fdt;
-static int reserve_mem_kho_finalize(struct kho_serialization *ser) -{
- int err = 0, i;
- for (i = 0; i < reserved_mem_count; i++) {
struct reserve_mem_table *map = &reserved_mem_table[i];struct page *page = phys_to_page(map->start);unsigned int nr_pages = map->size >> PAGE_SHIFT;err |= kho_preserve_pages(page, nr_pages);- }
- err |= kho_preserve_folio(page_folio(kho_fdt));
- err |= kho_add_subtree(ser, MEMBLOCK_KHO_FDT, page_to_virt(kho_fdt));
- return notifier_from_errno(err);
-}
-static int reserve_mem_kho_notifier(struct notifier_block *self,
unsigned long cmd, void *v)-{
- switch (cmd) {
- case KEXEC_KHO_FINALIZE:
return reserve_mem_kho_finalize((struct kho_serialization *)v);- case KEXEC_KHO_ABORT:
return NOTIFY_DONE;- default:
return NOTIFY_BAD;- }
-}
-static struct notifier_block reserve_mem_kho_nb = {
- .notifier_call = reserve_mem_kho_notifier,
-}; static int __init prepare_kho_fdt(void) { int err = 0, i;
- struct page *fdt_page; void *fdt;
- kho_fdt = alloc_page(GFP_KERNEL);
- if (!kho_fdt)
- fdt_page = alloc_page(GFP_KERNEL);
- if (!fdt_page) return -ENOMEM;
- fdt = page_to_virt(kho_fdt);
- fdt = page_to_virt(fdt_page);
err |= fdt_create(fdt, PAGE_SIZE); err |= fdt_finish_reservemap(fdt); @@ -2499,7 +2464,10 @@ static int __init prepare_kho_fdt(void) err |= fdt_property_string(fdt, "compatible", MEMBLOCK_KHO_NODE_COMPATIBLE); for (i = 0; i < reserved_mem_count; i++) { struct reserve_mem_table *map = &reserved_mem_table[i];
struct page *page = phys_to_page(map->start);unsigned int nr_pages = map->size >> PAGE_SHIFT;
err |= kho_preserve_pages(page, nr_pages);@@ -2507,13 +2475,16 @@ static int __init prepare_kho_fdt(void) err |= fdt_end_node(fdt); } err |= fdt_end_node(fdt);
- err |= fdt_finish(fdt);
- err |= kho_preserve_folio(page_folio(fdt_page));
- if (!err)
err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt);- if (err) { pr_err("failed to prepare memblock FDT for KHO: %d\n", err);
put_page(kho_fdt);kho_fdt = NULL;
put_page(fdt_page);return err; @@ -2529,13 +2500,6 @@ static int __init reserve_mem_init(void) err = prepare_kho_fdt(); if (err) return err;
- err = register_kho_notifier(&reserve_mem_kho_nb);
- if (err) {
put_page(kho_fdt);kho_fdt = NULL;- }
- return err;
} late_initcall(reserve_mem_init);
On Wed, Oct 22, 2025 at 01:01:08PM +0200, Pratyush Yadav wrote:
Hi Pasha,
On Tue, Oct 21 2025, Pasha Tatashin wrote:
From: "Mike Rapoport (Microsoft)" rppt@kernel.org
The KHO framework uses a notifier chain as the mechanism for clients to participate in the finalization process. While this works for a single, central state machine, it is too restrictive for kernel-internal components like pstore/reserve_mem or IMA. These components need a simpler, direct way to register their state for preservation (e.g., during their initcall) without being part of a complex, shutdown-time notifier sequence. The notifier model forces all participants into a single finalization flow and makes direct preservation from an arbitrary context difficult. This patch refactors the client participation model by removing the notifier chain and introducing a direct API for managing FDT subtrees.
The core kho_finalize() and kho_abort() state machine remains, but clients now register their data with KHO beforehand.
...
@@ -1280,7 +1298,7 @@ static __init int kho_init(void) kho_enable = false; return err; } -late_initcall(kho_init); +fs_initcall(kho_init);
Is this change related to this patch? Also, why fs_initcall?
memblock registers sub-fdt in late_initcall(), so we should have the root fdt ready by then.
-- Regards, Pratyush Yadav
On Fri, Oct 24 2025, Mike Rapoport wrote:
On Wed, Oct 22, 2025 at 01:01:08PM +0200, Pratyush Yadav wrote:
Hi Pasha,
On Tue, Oct 21 2025, Pasha Tatashin wrote:
From: "Mike Rapoport (Microsoft)" rppt@kernel.org
The KHO framework uses a notifier chain as the mechanism for clients to participate in the finalization process. While this works for a single, central state machine, it is too restrictive for kernel-internal components like pstore/reserve_mem or IMA. These components need a simpler, direct way to register their state for preservation (e.g., during their initcall) without being part of a complex, shutdown-time notifier sequence. The notifier model forces all participants into a single finalization flow and makes direct preservation from an arbitrary context difficult. This patch refactors the client participation model by removing the notifier chain and introducing a direct API for managing FDT subtrees.
The core kho_finalize() and kho_abort() state machine remains, but clients now register their data with KHO beforehand.
...
@@ -1280,7 +1298,7 @@ static __init int kho_init(void) kho_enable = false; return err; } -late_initcall(kho_init); +fs_initcall(kho_init);
Is this change related to this patch? Also, why fs_initcall?
memblock registers sub-fdt in late_initcall(), so we should have the root fdt ready by then.
I see. Should this be even earlier then? Other components might also depend on KHO being initialized, and those might be at or before fs_initcall.
For example, LUO does its init using early_initcall and uses KHO, even before it is initialized [0]. This works because kho_retrieve_subtree() only uses parts initialized very early in boot (the KHO FDT), but I suppose we want to have a proper initialization order to not rely on things that just happen to work until they don't.
Since kho_init() has a dependency on debugfs, which gets initialized in core_initcall, I guess the earliest it can be is postcore_initcall. Or, we split out the debugfs parts into a separate init function (they have their own file anyway) and initialize "core KHO" in early_initcall? Then LUO can be in core_initcall and all its users in later ones.
Thoughts?
[0] https://lore.kernel.org/lkml/20250929010321.3462457-9-pasha.tatashin@soleen....
-int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
int err = 0;u64 phys = (u64)virt_to_phys(fdt);void *root = page_to_virt(ser->fdt);
struct kho_sub_fdt *sub_fdt;int err;
err |= fdt_begin_node(root, name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);
sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);if (!sub_fdt)return -ENOMEM;
if (err)return err;
INIT_LIST_HEAD(&sub_fdt->l);sub_fdt->name = name;sub_fdt->fdt = fdt;
return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
mutex_lock(&kho_out.fdts_lock);list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
I think, it is better to simply do: WARN_ON_ONCE(kho_debugfs_fdt_add(...)); Now debugfs is optional, and there is no reason to return an error to a caller if kho_debugfs_fdt_add() fails
mutex_unlock(&kho_out.fdts_lock);return err;} EXPORT_SYMBOL_GPL(kho_add_subtree);
-int register_kho_notifier(struct notifier_block *nb) +void kho_remove_subtree(void *fdt) {
return blocking_notifier_chain_register(&kho_out.chain_head, nb);-} -EXPORT_SYMBOL_GPL(register_kho_notifier);
struct kho_sub_fdt *sub_fdt;mutex_lock(&kho_out.fdts_lock);list_for_each_entry(sub_fdt, &kho_out.sub_fdts, l) {list_for_each_entry_safe() here since we delete.
Not needed, we are breaking from the iterator when deleting.
bool kho_finalized(void) @@ -1232,15 +1248,17 @@ static __init int kho_init(void) { int err = 0; const void *fdt = kho_get_fdt();
struct page *fdt_page; if (!kho_enable) return 0;
kho_out.ser.fdt = alloc_page(GFP_KERNEL);if (!kho_out.ser.fdt) {
fdt_page = alloc_page(GFP_KERNEL);if (!fdt_page) { err = -ENOMEM; goto err_free_scratch; }kho_out.fdt = page_to_virt(fdt_page); err = kho_debugfs_init(); if (err)@@ -1268,8 +1286,8 @@ static __init int kho_init(void) return 0;
err_free_fdt:
put_page(kho_out.ser.fdt);kho_out.ser.fdt = NULL;
put_page(fdt_page);kho_out.fdt = NULL;err_free_scratch: for (int i = 0; i < kho_scratch_cnt; i++) { void *start = __va(kho_scratch[i].addr); @@ -1280,7 +1298,7 @@ static __init int kho_init(void) kho_enable = false; return err; } -late_initcall(kho_init); +fs_initcall(kho_init);
Is this change related to this patch? Also, why fs_initcall?
static void __init kho_release_scratch(void) { @@ -1416,7 +1434,7 @@ int kho_fill_kimage(struct kimage *image) if (!kho_out.finalized) return 0;
image->kho.fdt = page_to_phys(kho_out.ser.fdt);
image->kho.fdt = virt_to_phys(kho_out.fdt); scratch_size = sizeof(*kho_scratch) * kho_scratch_cnt; scratch = (struct kexec_buf){diff --git a/kernel/kexec_handover_debugfs.c b/kernel/kexec_handover_debugfs.c index a91b279f1b23..46e9e6c0791f 100644 --- a/kernel/kexec_handover_debugfs.c +++ b/kernel/kexec_handover_debugfs.c @@ -61,14 +61,17 @@ int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name, return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt); }
-void kho_debugfs_cleanup(struct kho_debugfs *dbg) +void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt) {
struct fdt_debugfs *ff, *tmp;list_for_each_entry_safe(ff, tmp, &dbg->fdt_list, list) {debugfs_remove(ff->file);list_del(&ff->list);kfree(ff);
struct fdt_debugfs *ff;list_for_each_entry(ff, &dbg->fdt_list, list) {list_for_each_entry_safe() here too.
Not needed, we are breaking out on delete/free.
static int kho_test_save_data(struct kho_test_state *state, void *fdt) { phys_addr_t *folios_info __free(kvfree) = NULL; @@ -102,6 +86,9 @@ static int kho_test_save_data(struct kho_test_state *state, void *fdt) if (!err) state->folios_info = no_free_ptr(folios_info);
if (!err)err = kho_test();This name is very undescriptive. Also, not the right place to add the subtree since the FDT isn't finished yet. I think it should be done from kho_test_save() instead. This patch is also missing removing the subtree at exit, and that can cause a UAF.
I sent you a patch earlier with my take on how it should be done. I still think that is the way to go: https://lore.kernel.org/all/mafs0347woui2.fsf@kernel.org/
Sure, I updated to use your suggested changes.
On Fri, Oct 24 2025, Pasha Tatashin wrote:
-int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
int err = 0;u64 phys = (u64)virt_to_phys(fdt);void *root = page_to_virt(ser->fdt);
struct kho_sub_fdt *sub_fdt;int err;
err |= fdt_begin_node(root, name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);
sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);if (!sub_fdt)return -ENOMEM;
if (err)return err;
INIT_LIST_HEAD(&sub_fdt->l);sub_fdt->name = name;sub_fdt->fdt = fdt;
return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
mutex_lock(&kho_out.fdts_lock);list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
I think, it is better to simply do: WARN_ON_ONCE(kho_debugfs_fdt_add(...)); Now debugfs is optional, and there is no reason to return an error to a caller if kho_debugfs_fdt_add() fails
Yeah, that works too.
mutex_unlock(&kho_out.fdts_lock);return err;} EXPORT_SYMBOL_GPL(kho_add_subtree);
-int register_kho_notifier(struct notifier_block *nb) +void kho_remove_subtree(void *fdt) {
return blocking_notifier_chain_register(&kho_out.chain_head, nb);-} -EXPORT_SYMBOL_GPL(register_kho_notifier);
struct kho_sub_fdt *sub_fdt;mutex_lock(&kho_out.fdts_lock);list_for_each_entry(sub_fdt, &kho_out.sub_fdts, l) {list_for_each_entry_safe() here since we delete.
Not needed, we are breaking from the iterator when deleting.
Makes sense. Didn't think of that.
[...]
On Fri, Oct 24 2025, Pratyush Yadav wrote:
On Fri, Oct 24 2025, Pasha Tatashin wrote:
-int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
int err = 0;u64 phys = (u64)virt_to_phys(fdt);void *root = page_to_virt(ser->fdt);
struct kho_sub_fdt *sub_fdt;int err;
err |= fdt_begin_node(root, name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);
sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);if (!sub_fdt)return -ENOMEM;
if (err)return err;
INIT_LIST_HEAD(&sub_fdt->l);sub_fdt->name = name;sub_fdt->fdt = fdt;
return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
mutex_lock(&kho_out.fdts_lock);list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
I think, it is better to simply do: WARN_ON_ONCE(kho_debugfs_fdt_add(...)); Now debugfs is optional, and there is no reason to return an error to a caller if kho_debugfs_fdt_add() fails
Yeah, that works too.
On a second thought, maybe pr_warn() instead of WARN_ON()? This isn't an assertion since the debugfs creation can fail for many reasons. It isn't expected to always succeed. So a full WARN_ON() splat seems overkill.
[...]
On Fri, Oct 24, 2025 at 11:52 AM Pratyush Yadav pratyush@kernel.org wrote:
On Fri, Oct 24 2025, Pratyush Yadav wrote:
On Fri, Oct 24 2025, Pasha Tatashin wrote:
-int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
int err = 0;u64 phys = (u64)virt_to_phys(fdt);void *root = page_to_virt(ser->fdt);
struct kho_sub_fdt *sub_fdt;int err;
err |= fdt_begin_node(root, name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);
sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);if (!sub_fdt)return -ENOMEM;
if (err)return err;
INIT_LIST_HEAD(&sub_fdt->l);sub_fdt->name = name;sub_fdt->fdt = fdt;
return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
mutex_lock(&kho_out.fdts_lock);list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
I think, it is better to simply do: WARN_ON_ONCE(kho_debugfs_fdt_add(...)); Now debugfs is optional, and there is no reason to return an error to a caller if kho_debugfs_fdt_add() fails
Yeah, that works too.
On a second thought, maybe pr_warn() instead of WARN_ON()? This isn't an assertion since the debugfs creation can fail for many reasons. It isn't expected to always succeed. So a full WARN_ON() splat seems overkill.
I sent it with WARN_ON_ONCE(), I can change it to pr_warn_once() if there is another revision, otherwise we can just send a separate patch to make the change it is not that important.
Pasha
[...]
-- Regards, Pratyush Yadav
On Fri, Oct 24 2025, Pasha Tatashin wrote:
On Fri, Oct 24, 2025 at 11:52 AM Pratyush Yadav pratyush@kernel.org wrote:
On Fri, Oct 24 2025, Pratyush Yadav wrote:
On Fri, Oct 24 2025, Pasha Tatashin wrote:
-int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt) +int kho_add_subtree(const char *name, void *fdt) {
int err = 0;u64 phys = (u64)virt_to_phys(fdt);void *root = page_to_virt(ser->fdt);
struct kho_sub_fdt *sub_fdt;int err;
err |= fdt_begin_node(root, name);err |= fdt_property(root, PROP_SUB_FDT, &phys, sizeof(phys));err |= fdt_end_node(root);
sub_fdt = kmalloc(sizeof(*sub_fdt), GFP_KERNEL);if (!sub_fdt)return -ENOMEM;
if (err)return err;
INIT_LIST_HEAD(&sub_fdt->l);sub_fdt->name = name;sub_fdt->fdt = fdt;
return kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);
mutex_lock(&kho_out.fdts_lock);list_add_tail(&sub_fdt->l, &kho_out.sub_fdts);err = kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false);I think you should remove sub_fdt from the list and kfree() it on error here. Otherwise we signal an error to the caller and they might free sub_fdt->fdt, which will later result in a use-after-free at __kho_finalize().
I think, it is better to simply do: WARN_ON_ONCE(kho_debugfs_fdt_add(...)); Now debugfs is optional, and there is no reason to return an error to a caller if kho_debugfs_fdt_add() fails
Yeah, that works too.
On a second thought, maybe pr_warn() instead of WARN_ON()? This isn't an assertion since the debugfs creation can fail for many reasons. It isn't expected to always succeed. So a full WARN_ON() splat seems overkill.
I sent it with WARN_ON_ONCE(), I can change it to pr_warn_once() if there is another revision, otherwise we can just send a separate patch to make the change it is not that important.
Yep, makes sense.
Allow users of KHO to cancel the previous preservation by adding the necessary interfaces to unpreserve folio and pages.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- include/linux/kexec_handover.h | 12 +++++ kernel/kexec_handover.c | 85 ++++++++++++++++++++++++++++------ 2 files changed, 84 insertions(+), 13 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 2faf290803ce..4ba145713838 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -43,7 +43,9 @@ bool kho_is_enabled(void); bool is_kho_boot(void);
int kho_preserve_folio(struct folio *folio); +int kho_unpreserve_folio(struct folio *folio); int kho_preserve_pages(struct page *page, unsigned int nr_pages); +int kho_unpreserve_pages(struct page *page, unsigned int nr_pages); int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); struct folio *kho_restore_folio(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages); @@ -76,11 +78,21 @@ static inline int kho_preserve_folio(struct folio *folio) return -EOPNOTSUPP; }
+static inline int kho_unpreserve_folio(struct folio *folio) +{ + return -EOPNOTSUPP; +} + static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages) { return -EOPNOTSUPP; }
+static inline int kho_unpreserve_pages(struct page *page, unsigned int nr_pages) +{ + return -EOPNOTSUPP; +} + static inline int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation) { diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 0a4234269fe5..8412897385ad 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -157,26 +157,33 @@ static void *xa_load_or_alloc(struct xarray *xa, unsigned long index) return no_free_ptr(elm); }
-static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn, - unsigned long end_pfn) +static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned long pfn, + unsigned int order) { struct kho_mem_phys_bits *bits; struct kho_mem_phys *physxa; + const unsigned long pfn_high = pfn >> order;
- while (pfn < end_pfn) { - const unsigned int order = - min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); - const unsigned long pfn_high = pfn >> order; + physxa = xa_load(&track->orders, order); + if (!physxa) + return; + + bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS); + if (!bits) + return;
- physxa = xa_load(&track->orders, order); - if (!physxa) - continue; + clear_bit(pfn_high % PRESERVE_BITS, bits->preserve); +} + +static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn, + unsigned long end_pfn) +{ + unsigned int order;
- bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS); - if (!bits) - continue; + while (pfn < end_pfn) { + order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
- clear_bit(pfn_high % PRESERVE_BITS, bits->preserve); + __kho_unpreserve_order(track, pfn, order);
pfn += 1 << order; } @@ -749,6 +756,30 @@ int kho_preserve_folio(struct folio *folio) } EXPORT_SYMBOL_GPL(kho_preserve_folio);
+/** + * kho_unpreserve_folio - unpreserve a folio. + * @folio: folio to unpreserve. + * + * Instructs KHO to unpreserve a folio that was preserved by + * kho_preserve_folio() before. The provided @folio (pfn and order) + * must exactly match a previously preserved folio. + * + * Return: 0 on success, error code on failure + */ +int kho_unpreserve_folio(struct folio *folio) +{ + const unsigned long pfn = folio_pfn(folio); + const unsigned int order = folio_order(folio); + struct kho_mem_track *track = &kho_out.track; + + if (kho_out.finalized) + return -EBUSY; + + __kho_unpreserve_order(track, pfn, order); + return 0; +} +EXPORT_SYMBOL_GPL(kho_unpreserve_folio); + /** * kho_preserve_pages - preserve contiguous pages across kexec * @page: first page in the list. @@ -793,6 +824,34 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages) } EXPORT_SYMBOL_GPL(kho_preserve_pages);
+/** + * kho_unpreserve_pages - unpreserve contiguous pages. + * @page: first page in the list. + * @nr_pages: number of pages. + * + * Instructs KHO to unpreserve @nr_pages contigious pages starting from @page. + * This call must exactly match a granularity at which memory was originally + * preserved by kho_preserve_pages, call with the same @page and + * @nr_pages). Unpreserving arbitrary sub-ranges of larger preserved blocks is + * not supported. + * + * Return: 0 on success, error code on failure + */ +int kho_unpreserve_pages(struct page *page, unsigned int nr_pages) +{ + struct kho_mem_track *track = &kho_out.track; + const unsigned long start_pfn = page_to_pfn(page); + const unsigned long end_pfn = start_pfn + nr_pages; + + if (kho_out.finalized) + return -EBUSY; + + __kho_unpreserve(track, start_pfn, end_pfn); + + return 0; +} +EXPORT_SYMBOL_GPL(kho_unpreserve_pages); + struct kho_vmalloc_hdr { DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *); };
On Tue, Oct 21 2025, Pasha Tatashin wrote:
Allow users of KHO to cancel the previous preservation by adding the necessary interfaces to unpreserve folio and pages.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
include/linux/kexec_handover.h | 12 +++++ kernel/kexec_handover.c | 85 ++++++++++++++++++++++++++++------ 2 files changed, 84 insertions(+), 13 deletions(-)
[...]
+/**
- kho_unpreserve_pages - unpreserve contiguous pages.
- @page: first page in the list.
- @nr_pages: number of pages.
- Instructs KHO to unpreserve @nr_pages contigious pages starting from @page.
s/contigious/contiguous. Also drop the extra space after it.
- This call must exactly match a granularity at which memory was originally
- preserved by kho_preserve_pages, call with the same @page and
- @nr_pages). Unpreserving arbitrary sub-ranges of larger preserved blocks is
Stray closing parenthesis here. Perhaps a rewording to: "This must be called with the same @page and @nr_pages as the corresponding kho_preserve_pages() call. Unpreserving arbitrary..."
Other than this,
Reviewed-by: Pratyush Yadav pratyush@kernel.org
- not supported.
- Return: 0 on success, error code on failure
- */
+int kho_unpreserve_pages(struct page *page, unsigned int nr_pages) +{
- struct kho_mem_track *track = &kho_out.track;
- const unsigned long start_pfn = page_to_pfn(page);
- const unsigned long end_pfn = start_pfn + nr_pages;
- if (kho_out.finalized)
return -EBUSY;- __kho_unpreserve(track, start_pfn, end_pfn);
- return 0;
+} +EXPORT_SYMBOL_GPL(kho_unpreserve_pages);
struct kho_vmalloc_hdr { DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *); };
On Wed, Oct 22, 2025 at 7:10 AM Pratyush Yadav pratyush@kernel.org wrote:
On Tue, Oct 21 2025, Pasha Tatashin wrote:
Allow users of KHO to cancel the previous preservation by adding the necessary interfaces to unpreserve folio and pages.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
include/linux/kexec_handover.h | 12 +++++ kernel/kexec_handover.c | 85 ++++++++++++++++++++++++++++------ 2 files changed, 84 insertions(+), 13 deletions(-)
[...]
+/**
- kho_unpreserve_pages - unpreserve contiguous pages.
- @page: first page in the list.
- @nr_pages: number of pages.
- Instructs KHO to unpreserve @nr_pages contigious pages starting from @page.
s/contigious/contiguous. Also drop the extra space after it.
- This call must exactly match a granularity at which memory was originally
- preserved by kho_preserve_pages, call with the same @page and
- @nr_pages). Unpreserving arbitrary sub-ranges of larger preserved blocks is
Stray closing parenthesis here. Perhaps a rewording to: "This must be called with the same @page and @nr_pages as the corresponding kho_preserve_pages() call. Unpreserving arbitrary..."
Done.
Other than this,
Reviewed-by: Pratyush Yadav pratyush@kernel.org
Thank you.
On Tue, Oct 21, 2025 at 08:57:16PM -0400, Pasha Tatashin wrote:
Allow users of KHO to cancel the previous preservation by adding the necessary interfaces to unpreserve folio and pages.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
include/linux/kexec_handover.h | 12 +++++ kernel/kexec_handover.c | 85 ++++++++++++++++++++++++++++------ 2 files changed, 84 insertions(+), 13 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 2faf290803ce..4ba145713838 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -43,7 +43,9 @@ bool kho_is_enabled(void); bool is_kho_boot(void); int kho_preserve_folio(struct folio *folio); +int kho_unpreserve_folio(struct folio *folio); int kho_preserve_pages(struct page *page, unsigned int nr_pages); +int kho_unpreserve_pages(struct page *page, unsigned int nr_pages); int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); struct folio *kho_restore_folio(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned int nr_pages); @@ -76,11 +78,21 @@ static inline int kho_preserve_folio(struct folio *folio) return -EOPNOTSUPP; } +static inline int kho_unpreserve_folio(struct folio *folio) +{
- return -EOPNOTSUPP;
+}
static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages) { return -EOPNOTSUPP; } +static inline int kho_unpreserve_pages(struct page *page, unsigned int nr_pages) +{
- return -EOPNOTSUPP;
+}
static inline int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation) { diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 0a4234269fe5..8412897385ad 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -157,26 +157,33 @@ static void *xa_load_or_alloc(struct xarray *xa, unsigned long index) return no_free_ptr(elm); } -static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
unsigned long end_pfn)+static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned long pfn,
unsigned int order){ struct kho_mem_phys_bits *bits; struct kho_mem_phys *physxa;
- const unsigned long pfn_high = pfn >> order;
- while (pfn < end_pfn) {
const unsigned int order =min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));const unsigned long pfn_high = pfn >> order;
- physxa = xa_load(&track->orders, order);
- if (!physxa)
return;- bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
- if (!bits)
return;
physxa = xa_load(&track->orders, order);if (!physxa)continue;
- clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+}
+static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
unsigned long end_pfn)+{
- unsigned int order;
bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);if (!bits)continue;
- while (pfn < end_pfn) {
order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
__kho_unpreserve_order(track, pfn, order);pfn += 1 << order; } @@ -749,6 +756,30 @@ int kho_preserve_folio(struct folio *folio) } EXPORT_SYMBOL_GPL(kho_preserve_folio); +/**
- kho_unpreserve_folio - unpreserve a folio.
- @folio: folio to unpreserve.
- Instructs KHO to unpreserve a folio that was preserved by
- kho_preserve_folio() before. The provided @folio (pfn and order)
- must exactly match a previously preserved folio.
- Return: 0 on success, error code on failure
- */
+int kho_unpreserve_folio(struct folio *folio) +{
- const unsigned long pfn = folio_pfn(folio);
- const unsigned int order = folio_order(folio);
- struct kho_mem_track *track = &kho_out.track;
- if (kho_out.finalized)
return -EBUSY;- __kho_unpreserve_order(track, pfn, order);
- return 0;
+} +EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
/**
- kho_preserve_pages - preserve contiguous pages across kexec
- @page: first page in the list.
@@ -793,6 +824,34 @@ int kho_preserve_pages(struct page *page, unsigned int nr_pages) } EXPORT_SYMBOL_GPL(kho_preserve_pages); +/**
- kho_unpreserve_pages - unpreserve contiguous pages.
- @page: first page in the list.
- @nr_pages: number of pages.
- Instructs KHO to unpreserve @nr_pages contigious pages starting from @page.
- This call must exactly match a granularity at which memory was originally
- preserved by kho_preserve_pages, call with the same @page and
- @nr_pages). Unpreserving arbitrary sub-ranges of larger preserved blocks is
- not supported.
- Return: 0 on success, error code on failure
- */
+int kho_unpreserve_pages(struct page *page, unsigned int nr_pages) +{
- struct kho_mem_track *track = &kho_out.track;
- const unsigned long start_pfn = page_to_pfn(page);
- const unsigned long end_pfn = start_pfn + nr_pages;
- if (kho_out.finalized)
return -EBUSY;- __kho_unpreserve(track, start_pfn, end_pfn);
- return 0;
+} +EXPORT_SYMBOL_GPL(kho_unpreserve_pages);
struct kho_vmalloc_hdr { DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *); }; -- 2.51.0.915.g61a8936c21-goog
KHO allows clients to preserve memory regions at any point before the KHO state is finalized. The finalization process itself involves KHO performing its own actions, such as serializing the overall preserved memory map.
If this finalization process is aborted, the current implementation destroys KHO's internal memory tracking structures (`kho_out.ser.track.orders`). This behavior effectively unpreserves all memory from KHO's perspective, regardless of whether those preservations were made by clients before the finalization attempt or by KHO itself during finalization.
This premature unpreservation is incorrect. An abort of the finalization process should only undo actions taken by KHO as part of that specific finalization attempt. Individual memory regions preserved by clients prior to finalization should remain preserved, as their lifecycle is managed by the clients themselves. These clients might still need to call kho_unpreserve_folio() or kho_unpreserve_phys() based on their own logic, even after a KHO finalization attempt is aborted.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- kernel/kexec_handover.c | 21 +-------------------- 1 file changed, 1 insertion(+), 20 deletions(-)
diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 8412897385ad..89a3fa89db0a 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -1103,31 +1103,12 @@ EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
static int __kho_abort(void) { - int err = 0; - unsigned long order; - struct kho_mem_phys *physxa; - - xa_for_each(&kho_out.track.orders, order, physxa) { - struct kho_mem_phys_bits *bits; - unsigned long phys; - - xa_for_each(&physxa->phys_bits, phys, bits) - kfree(bits); - - xa_destroy(&physxa->phys_bits); - kfree(physxa); - } - xa_destroy(&kho_out.track.orders); - if (kho_out.preserved_mem_map) { kho_mem_ser_free(kho_out.preserved_mem_map); kho_out.preserved_mem_map = NULL; }
- if (err) - pr_err("Failed to abort KHO finalization: %d\n", err); - - return err; + return 0; }
int kho_abort(void)
On Tue, Oct 21 2025, Pasha Tatashin wrote:
KHO allows clients to preserve memory regions at any point before the KHO state is finalized. The finalization process itself involves KHO performing its own actions, such as serializing the overall preserved memory map.
If this finalization process is aborted, the current implementation destroys KHO's internal memory tracking structures (`kho_out.ser.track.orders`). This behavior effectively unpreserves all memory from KHO's perspective, regardless of whether those preservations were made by clients before the finalization attempt or by KHO itself during finalization.
This premature unpreservation is incorrect. An abort of the finalization process should only undo actions taken by KHO as part of that specific finalization attempt. Individual memory regions preserved by clients prior to finalization should remain preserved, as their lifecycle is managed by the clients themselves. These clients might still need to call kho_unpreserve_folio() or kho_unpreserve_phys() based on their own logic, even after a KHO finalization attempt is aborted.
I think you also need to update test_kho and reserve_mem to do this since right now they assume all memory gets unpreserved on failure.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
[...]
On Wed, Oct 22, 2025 at 01:15:30PM +0200, Pratyush Yadav wrote:
On Tue, Oct 21 2025, Pasha Tatashin wrote:
KHO allows clients to preserve memory regions at any point before the KHO state is finalized. The finalization process itself involves KHO performing its own actions, such as serializing the overall preserved memory map.
If this finalization process is aborted, the current implementation destroys KHO's internal memory tracking structures (`kho_out.ser.track.orders`). This behavior effectively unpreserves all memory from KHO's perspective, regardless of whether those preservations were made by clients before the finalization attempt or by KHO itself during finalization.
This premature unpreservation is incorrect. An abort of the finalization process should only undo actions taken by KHO as part of that specific finalization attempt. Individual memory regions preserved by clients prior to finalization should remain preserved, as their lifecycle is managed by the clients themselves. These clients might still need to call kho_unpreserve_folio() or kho_unpreserve_phys() based on their own logic, even after a KHO finalization attempt is aborted.
I think you also need to update test_kho and reserve_mem to do this since right now they assume all memory gets unpreserved on failure.
I agree.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com
[...]
-- Regards, Pratyush Yadav
On Thu, Oct 23, 2025 at 3:21 AM Mike Rapoport rppt@kernel.org wrote:
On Wed, Oct 22, 2025 at 01:15:30PM +0200, Pratyush Yadav wrote:
On Tue, Oct 21 2025, Pasha Tatashin wrote:
KHO allows clients to preserve memory regions at any point before the KHO state is finalized. The finalization process itself involves KHO performing its own actions, such as serializing the overall preserved memory map.
If this finalization process is aborted, the current implementation destroys KHO's internal memory tracking structures (`kho_out.ser.track.orders`). This behavior effectively unpreserves all memory from KHO's perspective, regardless of whether those preservations were made by clients before the finalization attempt or by KHO itself during finalization.
This premature unpreservation is incorrect. An abort of the finalization process should only undo actions taken by KHO as part of that specific finalization attempt. Individual memory regions preserved by clients prior to finalization should remain preserved, as their lifecycle is managed by the clients themselves. These clients might still need to call kho_unpreserve_folio() or kho_unpreserve_phys() based on their own logic, even after a KHO finalization attempt is aborted.
I think you also need to update test_kho and reserve_mem to do this since right now they assume all memory gets unpreserved on failure.
I agree.
Hm, this makes no sense to me. So, KHO tried to finalize (i.e., convert xarray to sparse bitmap) and failed (e.g. due to OOM) or aborted, so we aborted the finalization. But the preserved memory stays preserved, and if user/caller retries finalization and it succeeds, the preserved memory will still be passed to the next kernel. Why would reserve_mem and test_kho depend on whether KHO finalization succeeded or was canceled? It is possible that user cancel only to add something else to preservation.
Pasha
On Fri, Oct 24 2025, Pasha Tatashin wrote:
On Thu, Oct 23, 2025 at 3:21 AM Mike Rapoport rppt@kernel.org wrote:
On Wed, Oct 22, 2025 at 01:15:30PM +0200, Pratyush Yadav wrote:
On Tue, Oct 21 2025, Pasha Tatashin wrote:
KHO allows clients to preserve memory regions at any point before the KHO state is finalized. The finalization process itself involves KHO performing its own actions, such as serializing the overall preserved memory map.
If this finalization process is aborted, the current implementation destroys KHO's internal memory tracking structures (`kho_out.ser.track.orders`). This behavior effectively unpreserves all memory from KHO's perspective, regardless of whether those preservations were made by clients before the finalization attempt or by KHO itself during finalization.
This premature unpreservation is incorrect. An abort of the finalization process should only undo actions taken by KHO as part of that specific finalization attempt. Individual memory regions preserved by clients prior to finalization should remain preserved, as their lifecycle is managed by the clients themselves. These clients might still need to call kho_unpreserve_folio() or kho_unpreserve_phys() based on their own logic, even after a KHO finalization attempt is aborted.
I think you also need to update test_kho and reserve_mem to do this since right now they assume all memory gets unpreserved on failure.
I agree.
Hm, this makes no sense to me. So, KHO tried to finalize (i.e., convert xarray to sparse bitmap) and failed (e.g. due to OOM) or aborted, so we aborted the finalization. But the preserved memory stays preserved, and if user/caller retries finalization and it succeeds, the preserved memory will still be passed to the next kernel. Why would reserve_mem and test_kho depend on whether KHO finalization succeeded or was canceled? It is possible that user cancel only to add something else to preservation.
On mainline, the reserve_mem kho_preserve_pages() calls come from the notifier chain. Any failure on the notifier chain causes an abort and thus automatically unpreserves all pages that were preserved.
static int reserve_mem_kho_finalize(struct kho_serialization *ser) { int err = 0, i; for (i = 0; i < reserved_mem_count; i++) { [...] err |= kho_preserve_pages(page, nr_pages); } err |= kho_preserve_folio(page_folio(kho_fdt)); err |= kho_add_subtree(ser, MEMBLOCK_KHO_FDT, page_to_virt(kho_fdt)); return notifier_from_errno(err); }
If any of the kho_preserve_pages() fails, the notifier block will fail, cause an abort, and eventually all memory will be unpreserved.
Now that there is no notifier, and thus no abort, the pages must be unpreserved explicitly before returning.
Similarly, for test_kho, kho_test_notifier() calls kho_preserve_folio() and expects the abort to clean things up.
Side note: test_kho also preserves folios from kho_test_save_data() and doesn't clean them up on error, but that is a separate problem that this series doesn't have to solve.
I think patch 3/7 is the one that actually causes this problem since it gets rid of the notifier. This is the wrong patch to complain about this but somehow I thought this is the one that triggers it.
If any of the kho_preserve_pages() fails, the notifier block will fail, cause an abort, and eventually all memory will be unpreserved.
This is a wrong behavior. Why should the memory that I preserved be unpreserved if there is finailziation failure or abort? reserve_mem should still keep memory as preserved in case KHO later will be finalized right? I have tested that this patch works with kho self-test: preserve, finalize, abort, finalize again, and the pages are properly preserved.
KHO Test and memblock do not need to ever unpreserve pages, as they preserve them once during boot.
Now that there is no notifier, and thus no abort, the pages must be unpreserved explicitly before returning.
Similarly, for test_kho, kho_test_notifier() calls kho_preserve_folio() and expects the abort to clean things up.
Side note: test_kho also preserves folios from kho_test_save_data() and doesn't clean them up on error, but that is a separate problem that this series doesn't have to solve.
I think patch 3/7 is the one that actually causes this problem since it
I updated that patch with your suggested fix.
Pasha
On Fri, Oct 24 2025, Pasha Tatashin wrote:
If any of the kho_preserve_pages() fails, the notifier block will fail, cause an abort, and eventually all memory will be unpreserved.
This is a wrong behavior. Why should the memory that I preserved be unpreserved if there is finailziation failure or abort? reserve_mem should still keep memory as preserved in case KHO later will be finalized right? I have tested that this patch works with kho self-test: preserve, finalize, abort, finalize again, and the pages are properly preserved.
KHO Test and memblock do not need to ever unpreserve pages, as they preserve them once during boot.
Agreed. The behaviour of reserve_mem and test_kho should be fixed, patch 3 just exposes the problem.
So, for this patch
Reviewed-by: Pratyush Yadav pratyush@kernel.org
Now that there is no notifier, and thus no abort, the pages must be unpreserved explicitly before returning.
Similarly, for test_kho, kho_test_notifier() calls kho_preserve_folio() and expects the abort to clean things up.
Side note: test_kho also preserves folios from kho_test_save_data() and doesn't clean them up on error, but that is a separate problem that this series doesn't have to solve.
I think patch 3/7 is the one that actually causes this problem since it
I updated that patch with your suggested fix.
Thanks!
Move KHO to kernel/liveupdate/ in preparation of placing all Live Update core kernel related files to the same place.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com Reviewed-by: Jason Gunthorpe jgg@nvidia.com Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org --- Documentation/core-api/kho/concepts.rst | 2 +- MAINTAINERS | 2 +- init/Kconfig | 2 + kernel/Kconfig.kexec | 34 ---------------- kernel/Makefile | 4 +- kernel/liveupdate/Kconfig | 39 +++++++++++++++++++ kernel/liveupdate/Makefile | 5 +++ kernel/{ => liveupdate}/kexec_handover.c | 4 +- .../{ => liveupdate}/kexec_handover_debug.c | 0 .../{ => liveupdate}/kexec_handover_debugfs.c | 0 .../kexec_handover_internal.h | 0 11 files changed, 51 insertions(+), 41 deletions(-) create mode 100644 kernel/liveupdate/Kconfig create mode 100644 kernel/liveupdate/Makefile rename kernel/{ => liveupdate}/kexec_handover.c (99%) rename kernel/{ => liveupdate}/kexec_handover_debug.c (100%) rename kernel/{ => liveupdate}/kexec_handover_debugfs.c (100%) rename kernel/{ => liveupdate}/kexec_handover_internal.h (100%)
diff --git a/Documentation/core-api/kho/concepts.rst b/Documentation/core-api/kho/concepts.rst index 36d5c05cfb30..d626d1dbd678 100644 --- a/Documentation/core-api/kho/concepts.rst +++ b/Documentation/core-api/kho/concepts.rst @@ -70,5 +70,5 @@ in the FDT. That state is called the KHO finalization phase.
Public API ========== -.. kernel-doc:: kernel/kexec_handover.c +.. kernel-doc:: kernel/liveupdate/kexec_handover.c :export: diff --git a/MAINTAINERS b/MAINTAINERS index 0a6ba2717caa..eae55bb6ab4d 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13781,7 +13781,7 @@ S: Maintained F: Documentation/admin-guide/mm/kho.rst F: Documentation/core-api/kho/* F: include/linux/kexec_handover.h -F: kernel/kexec_handover* +F: kernel/liveupdate/kexec_handover* F: tools/testing/selftests/kho/
KEYS-ENCRYPTED diff --git a/init/Kconfig b/init/Kconfig index cab3ad28ca49..0605de5d96c0 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2138,6 +2138,8 @@ config TRACEPOINTS
source "kernel/Kconfig.kexec"
+source "kernel/liveupdate/Kconfig" + endmenu # General setup
source "arch/Kconfig" diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec index 9308a0fb1419..15632358bcf7 100644 --- a/kernel/Kconfig.kexec +++ b/kernel/Kconfig.kexec @@ -94,40 +94,6 @@ config KEXEC_JUMP Jump between original kernel and kexeced kernel and invoke code in physical address mode via KEXEC
-config KEXEC_HANDOVER - bool "kexec handover" - depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE - depends on !DEFERRED_STRUCT_PAGE_INIT - select MEMBLOCK_KHO_SCRATCH - select KEXEC_FILE - select DEBUG_FS - select LIBFDT - select CMA - help - Allow kexec to hand over state across kernels by generating and - passing additional metadata to the target kernel. This is useful - to keep data or state alive across the kexec. For this to work, - both source and target kernels need to have this option enabled. - -config KEXEC_HANDOVER_DEBUG - bool "Enable Kexec Handover debug checks" - depends on KEXEC_HANDOVER_DEBUGFS - help - This option enables extra sanity checks for the Kexec Handover - subsystem. Since, KHO performance is crucial in live update - scenarios and the extra code might be adding overhead it is - only optionally enabled. - -config KEXEC_HANDOVER_DEBUGFS - bool "kexec handover debugfs interface" - depends on KEXEC_HANDOVER - depends on DEBUG_FS - help - Allow to control kexec handover device tree via debugfs - interface, i.e. finalize the state or aborting the finalization. - Also, enables inspecting the KHO fdt trees with the debugfs binary - blobs. - config CRASH_DUMP bool "kernel crash dumps" default ARCH_DEFAULT_CRASH_DUMP diff --git a/kernel/Makefile b/kernel/Makefile index 2cf7909a74e5..e83669841b8c 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -52,6 +52,7 @@ obj-y += printk/ obj-y += irq/ obj-y += rcu/ obj-y += livepatch/ +obj-y += liveupdate/ obj-y += dma/ obj-y += entry/ obj-y += unwind/ @@ -82,9 +83,6 @@ obj-$(CONFIG_CRASH_DUMP_KUNIT_TEST) += crash_core_test.o obj-$(CONFIG_KEXEC) += kexec.o obj-$(CONFIG_KEXEC_FILE) += kexec_file.o obj-$(CONFIG_KEXEC_ELF) += kexec_elf.o -obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o -obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o -obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS) += kexec_handover_debugfs.o obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o obj-$(CONFIG_COMPAT) += compat.o obj-$(CONFIG_CGROUPS) += cgroup/ diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig new file mode 100644 index 000000000000..ae8bdd87458a --- /dev/null +++ b/kernel/liveupdate/Kconfig @@ -0,0 +1,39 @@ +# SPDX-License-Identifier: GPL-2.0-only + +menu "Live Update and Kexec HandOver" + +config KEXEC_HANDOVER + bool "kexec handover" + depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE + depends on !DEFERRED_STRUCT_PAGE_INIT + select MEMBLOCK_KHO_SCRATCH + select KEXEC_FILE + select DEBUG_FS + select LIBFDT + select CMA + help + Allow kexec to hand over state across kernels by generating and + passing additional metadata to the target kernel. This is useful + to keep data or state alive across the kexec. For this to work, + both source and target kernels need to have this option enabled. + +config KEXEC_HANDOVER_DEBUG + bool "Enable Kexec Handover debug checks" + depends on KEXEC_HANDOVER_DEBUGFS + help + This option enables extra sanity checks for the Kexec Handover + subsystem. Since, KHO performance is crucial in live update + scenarios and the extra code might be adding overhead it is + only optionally enabled. + +config KEXEC_HANDOVER_DEBUGFS + bool "kexec handover debugfs interface" + depends on KEXEC_HANDOVER + depends on DEBUG_FS + help + Allow to control kexec handover device tree via debugfs + interface, i.e. finalize the state or aborting the finalization. + Also, enables inspecting the KHO fdt trees with the debugfs binary + blobs. + +endmenu diff --git a/kernel/liveupdate/Makefile b/kernel/liveupdate/Makefile new file mode 100644 index 000000000000..f52ce1ebcf86 --- /dev/null +++ b/kernel/liveupdate/Makefile @@ -0,0 +1,5 @@ +# SPDX-License-Identifier: GPL-2.0 + +obj-$(CONFIG_KEXEC_HANDOVER) += kexec_handover.o +obj-$(CONFIG_KEXEC_HANDOVER_DEBUG) += kexec_handover_debug.o +obj-$(CONFIG_KEXEC_HANDOVER_DEBUGFS) += kexec_handover_debugfs.o diff --git a/kernel/kexec_handover.c b/kernel/liveupdate/kexec_handover.c similarity index 99% rename from kernel/kexec_handover.c rename to kernel/liveupdate/kexec_handover.c index 89a3fa89db0a..a1b97cc37cea 100644 --- a/kernel/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -26,8 +26,8 @@ * KHO is tightly coupled with mm init and needs access to some of mm * internal APIs. */ -#include "../mm/internal.h" -#include "kexec_internal.h" +#include "../../mm/internal.h" +#include "../kexec_internal.h" #include "kexec_handover_internal.h"
#define KHO_FDT_COMPATIBLE "kho-v1" diff --git a/kernel/kexec_handover_debug.c b/kernel/liveupdate/kexec_handover_debug.c similarity index 100% rename from kernel/kexec_handover_debug.c rename to kernel/liveupdate/kexec_handover_debug.c diff --git a/kernel/kexec_handover_debugfs.c b/kernel/liveupdate/kexec_handover_debugfs.c similarity index 100% rename from kernel/kexec_handover_debugfs.c rename to kernel/liveupdate/kexec_handover_debugfs.c diff --git a/kernel/kexec_handover_internal.h b/kernel/liveupdate/kexec_handover_internal.h similarity index 100% rename from kernel/kexec_handover_internal.h rename to kernel/liveupdate/kexec_handover_internal.h
Now, that LUO and KHO both live under kernel/liveupdate, it makes sense to also move the kho debugfs files to liveupdate/
The old names: /sys/kernel/debug/kho/out/ /sys/kernel/debug/kho/in/
The new names: /sys/kernel/debug/liveupdate/kho_out/ /sys/kernel/debug/liveupdate/kho_in/
Also, export the liveupdate_debufs_root, so future LUO selftests could use it as well.
Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com --- kernel/liveupdate/kexec_handover_debugfs.c | 10 +++++----- kernel/liveupdate/kexec_handover_internal.h | 2 ++ tools/testing/selftests/kho/init.c | 2 +- 3 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/liveupdate/kexec_handover_debugfs.c b/kernel/liveupdate/kexec_handover_debugfs.c index 46e9e6c0791f..454b7d34ddc3 100644 --- a/kernel/liveupdate/kexec_handover_debugfs.c +++ b/kernel/liveupdate/kexec_handover_debugfs.c @@ -15,7 +15,7 @@ #include <linux/mm.h> #include "kexec_handover_internal.h"
-static struct dentry *debugfs_root; +struct dentry *liveupdate_debugfs_root;
struct fdt_debugfs { struct list_head list; @@ -118,7 +118,7 @@ __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
INIT_LIST_HEAD(&dbg->fdt_list);
- dir = debugfs_create_dir("in", debugfs_root); + dir = debugfs_create_dir("kho_in", liveupdate_debugfs_root); if (IS_ERR(dir)) { err = PTR_ERR(dir); goto err_out; @@ -178,7 +178,7 @@ __init int kho_out_debugfs_init(struct kho_debugfs *dbg)
INIT_LIST_HEAD(&dbg->fdt_list);
- dir = debugfs_create_dir("out", debugfs_root); + dir = debugfs_create_dir("kho_out", liveupdate_debugfs_root); if (IS_ERR(dir)) return -ENOMEM;
@@ -212,8 +212,8 @@ __init int kho_out_debugfs_init(struct kho_debugfs *dbg)
__init int kho_debugfs_init(void) { - debugfs_root = debugfs_create_dir("kho", NULL); - if (IS_ERR(debugfs_root)) + liveupdate_debugfs_root = debugfs_create_dir("liveupdate", NULL); + if (IS_ERR(liveupdate_debugfs_root)) return -ENOENT; return 0; } diff --git a/kernel/liveupdate/kexec_handover_internal.h b/kernel/liveupdate/kexec_handover_internal.h index 17ae101dc6ae..92798346fa5a 100644 --- a/kernel/liveupdate/kexec_handover_internal.h +++ b/kernel/liveupdate/kexec_handover_internal.h @@ -15,6 +15,8 @@ struct kho_debugfs { struct list_head fdt_list; };
+extern struct dentry *liveupdate_debugfs_root; + #else struct kho_debugfs {}; #endif diff --git a/tools/testing/selftests/kho/init.c b/tools/testing/selftests/kho/init.c index 6d9e91d55d68..f0136a30ce8b 100644 --- a/tools/testing/selftests/kho/init.c +++ b/tools/testing/selftests/kho/init.c @@ -11,7 +11,7 @@ /* from arch/x86/include/asm/setup.h */ #define COMMAND_LINE_SIZE 2048
-#define KHO_FINALIZE "/debugfs/kho/out/finalize" +#define KHO_FINALIZE "/debugfs/liveupdate/kho_out/finalize" #define KERNEL_IMAGE "/kernel"
static int mount_filesystems(void)
On Tue, Oct 21, 2025 at 08:57:19PM -0400, Pasha Tatashin wrote:
Now, that LUO and KHO both live under kernel/liveupdate, it makes sense to also move the kho debugfs files to liveupdate/
But we don't have LUO yet :/
The old names: /sys/kernel/debug/kho/out/ /sys/kernel/debug/kho/in/
The new names: /sys/kernel/debug/liveupdate/kho_out/ /sys/kernel/debug/liveupdate/kho_in/
Also, export the liveupdate_debufs_root, so future LUO selftests could use it as well.
Let's postpone this change until then. TBH, I don't see anything wrong with KHO and LUO selftest debugfs files living at the top level, i.e
/sys/kernel/debug/kho/ /sys/kernel/debug/luo_selftest
On Thu, Oct 23, 2025 at 3:32 AM Mike Rapoport rppt@kernel.org wrote:
On Tue, Oct 21, 2025 at 08:57:19PM -0400, Pasha Tatashin wrote:
Now, that LUO and KHO both live under kernel/liveupdate, it makes sense to also move the kho debugfs files to liveupdate/
But we don't have LUO yet :/
Yes, I need to update the comment :-)
The old names: /sys/kernel/debug/kho/out/ /sys/kernel/debug/kho/in/
The new names: /sys/kernel/debug/liveupdate/kho_out/ /sys/kernel/debug/liveupdate/kho_in/
Also, export the liveupdate_debufs_root, so future LUO selftests could use it as well.
Let's postpone this change until then. TBH, I don't see anything wrong with KHO and LUO selftest debugfs files living at the top level, i.e
It is not only about selftests, we are planning to add kexec telemetry that is going to be using KHO, and that should also be placed in the same directory. Let's keep them neatly in the same root directory, so we can use them for LUO/KHO/Telemetry and perhaps for other reasons.
I also think, this patch is small, so it would be beneficial to land it now, and make it easier for LUO, and soon to be sent out the Telemetry series.
Pasha
linux-kselftest-mirror@lists.linaro.org
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Mike Rapoport -
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Pratyush Yadav