From: Elliot Berman quic_eberman@quicinc.com

When guest_memfd removes memory from the host kernel's direct map, direct map entries must be restored before the memory is freed again. To do so, ->free_folio() needs to know whether a gmem folio was direct map removed in the first place though. While possible to keep track of this information on each individual folio (e.g. via page flags), direct map removal is an all-or-nothing property of the entire guest_memfd, so it is less error prone to just check the flag stored in the gmem inode's private data. However, by the time ->free_folio() is called, folio->mapping might be cleared. To still allow access to the address space from which the folio was just removed, pass it in as an additional argument to ->free_folio, as the mapping is well-known to all callers.

Link: https://lore.kernel.org/all/15f665b4-2d33-41ca-ac50-fafe24ade32f@redhat.com/ Suggested-by: David Hildenbrand david@redhat.com Acked-by: David Hildenbrand david@redhat.com Signed-off-by: Elliot Berman quic_eberman@quicinc.com [patrick: rewrite shortlog for new usecase] Signed-off-by: Patrick Roy roypat@amazon.co.uk --- Documentation/filesystems/locking.rst | 2 +- fs/nfs/dir.c | 11 ++++++----- fs/orangefs/inode.c | 3 ++- include/linux/fs.h | 2 +- mm/filemap.c | 9 +++++---- mm/secretmem.c | 3 ++- mm/vmscan.c | 4 ++-- virt/kvm/guest_memfd.c | 3 ++- 8 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index aa287ccdac2f..74c97287ec40 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -262,7 +262,7 @@ prototypes:: sector_t (*bmap)(struct address_space *, sector_t); void (*invalidate_folio) (struct folio *, size_t start, size_t len); bool (*release_folio)(struct folio *, gfp_t); - void (*free_folio)(struct folio *); + void (*free_folio)(struct address_space *, struct folio *); int (*direct_IO)(struct kiocb *, struct iov_iter *iter); int (*migrate_folio)(struct address_space *, struct folio *dst, struct folio *src, enum migrate_mode); diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index d81217923936..644bd54e052c 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -55,7 +55,7 @@ static int nfs_closedir(struct inode *, struct file *); static int nfs_readdir(struct file *, struct dir_context *); static int nfs_fsync_dir(struct file *, loff_t, loff_t, int); static loff_t nfs_llseek_dir(struct file *, loff_t, int); -static void nfs_readdir_clear_array(struct folio *); +static void nfs_readdir_clear_array(struct address_space *, struct folio *); static int nfs_do_create(struct inode *dir, struct dentry *dentry, umode_t mode, int open_flags);

@@ -218,7 +218,8 @@ static void nfs_readdir_folio_init_array(struct folio *folio, u64 last_cookie, /* * we are freeing strings created by nfs_add_to_readdir_array() */ -static void nfs_readdir_clear_array(struct folio *folio) +static void nfs_readdir_clear_array(struct address_space *mapping, + struct folio *folio) { struct nfs_cache_array *array; unsigned int i; @@ -233,7 +234,7 @@ static void nfs_readdir_clear_array(struct folio *folio) static void nfs_readdir_folio_reinit_array(struct folio *folio, u64 last_cookie, u64 change_attr) { - nfs_readdir_clear_array(folio); + nfs_readdir_clear_array(folio->mapping, folio); nfs_readdir_folio_init_array(folio, last_cookie, change_attr); }

@@ -249,7 +250,7 @@ nfs_readdir_folio_array_alloc(u64 last_cookie, gfp_t gfp_flags) static void nfs_readdir_folio_array_free(struct folio *folio) { if (folio) { - nfs_readdir_clear_array(folio); + nfs_readdir_clear_array(folio->mapping, folio); folio_put(folio); } } @@ -391,7 +392,7 @@ static void nfs_readdir_folio_init_and_validate(struct folio *folio, u64 cookie, if (folio_test_uptodate(folio)) { if (nfs_readdir_folio_validate(folio, cookie, change_attr)) return; - nfs_readdir_clear_array(folio); + nfs_readdir_clear_array(folio->mapping, folio); } nfs_readdir_folio_init_array(folio, cookie, change_attr); folio_mark_uptodate(folio); diff --git a/fs/orangefs/inode.c b/fs/orangefs/inode.c index a01400cd41fd..37227ba71593 100644 --- a/fs/orangefs/inode.c +++ b/fs/orangefs/inode.c @@ -452,7 +452,8 @@ static bool orangefs_release_folio(struct folio *folio, gfp_t foo) return !folio_test_private(folio); }

-static void orangefs_free_folio(struct folio *folio) +static void orangefs_free_folio(struct address_space *mapping, + struct folio *folio) { kfree(folio_detach_private(folio)); } diff --git a/include/linux/fs.h b/include/linux/fs.h index d7ab4f96d705..afb0748ffda6 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -457,7 +457,7 @@ struct address_space_operations { sector_t (*bmap)(struct address_space *, sector_t); void (*invalidate_folio) (struct folio *, size_t offset, size_t len); bool (*release_folio)(struct folio *, gfp_t); - void (*free_folio)(struct folio *folio); + void (*free_folio)(struct address_space *, struct folio *folio); ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter); /* * migrate the contents of a folio to the specified target. If diff --git a/mm/filemap.c b/mm/filemap.c index 751838ef05e5..3dd8ad922d80 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -226,11 +226,11 @@ void __filemap_remove_folio(struct folio *folio, void *shadow)

void filemap_free_folio(struct address_space *mapping, struct folio *folio) { - void (*free_folio)(struct folio *); + void (*free_folio)(struct address_space *, struct folio *);

free_folio = mapping->a_ops->free_folio; if (free_folio) - free_folio(folio); + free_folio(mapping, folio);

folio_put_refs(folio, folio_nr_pages(folio)); } @@ -820,7 +820,8 @@ EXPORT_SYMBOL(file_write_and_wait_range); void replace_page_cache_folio(struct folio *old, struct folio *new) { struct address_space *mapping = old->mapping; - void (*free_folio)(struct folio *) = mapping->a_ops->free_folio; + void (*free_folio)(struct address_space *, struct folio *) = + mapping->a_ops->free_folio; pgoff_t offset = old->index; XA_STATE(xas, &mapping->i_pages, offset);

@@ -849,7 +850,7 @@ void replace_page_cache_folio(struct folio *old, struct folio *new) __lruvec_stat_add_folio(new, NR_SHMEM); xas_unlock_irq(&xas); if (free_folio) - free_folio(old); + free_folio(mapping, old); folio_put(old); } EXPORT_SYMBOL_GPL(replace_page_cache_folio); diff --git a/mm/secretmem.c b/mm/secretmem.c index 60137305bc20..422dcaa32506 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -150,7 +150,8 @@ static int secretmem_migrate_folio(struct address_space *mapping, return -EBUSY; }

-static void secretmem_free_folio(struct folio *folio) +static void secretmem_free_folio(struct address_space *mapping, + struct folio *folio) { set_direct_map_default_noflush(folio_page(folio, 0)); folio_zero_segment(folio, 0, folio_size(folio)); diff --git a/mm/vmscan.c b/mm/vmscan.c index a48aec8bfd92..559bd6ac965c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -788,7 +788,7 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, xa_unlock_irq(&mapping->i_pages); put_swap_folio(folio, swap); } else { - void (*free_folio)(struct folio *); + void (*free_folio)(struct address_space *, struct folio *);

free_folio = mapping->a_ops->free_folio; /* @@ -817,7 +817,7 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, spin_unlock(&mapping->host->i_lock);

if (free_folio) - free_folio(folio); + free_folio(mapping, folio); }

return 1; diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 08a6bc7d25b6..9ec4c45e3cf2 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -430,7 +430,8 @@ static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *fol }

#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE -static void kvm_gmem_free_folio(struct folio *folio) +static void kvm_gmem_free_folio(struct address_space *mapping, + struct folio *folio) { struct page *page = folio_page(folio, 0); kvm_pfn_t pfn = page_to_pfn(page);

Use the new per-module export functionality to allow KVM (and only KVM) access to set_direct_map_valid_noflush(). This allows guest_memfd to remove its memory from the direct map, even if KVM is built as a module.

Direct map removal gives guest_memfd the same protection that memfd_secret enjoys, such as hardening against Spectre-like attacks through in-kernel gadgets.

Reviewed-by: Fuad Tabba tabba@google.com Signed-off-by: Patrick Roy roypat@amazon.co.uk --- arch/arm64/mm/pageattr.c | 1 + arch/loongarch/mm/pageattr.c | 1 + arch/riscv/mm/pageattr.c | 1 + arch/s390/mm/pageattr.c | 1 + arch/x86/mm/pat/set_memory.c | 1 + 5 files changed, 5 insertions(+)

diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 04d4a8f676db..4f3cddfab9b0 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -291,6 +291,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)

return set_memory_valid(addr, nr, valid); } +EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");

#ifdef CONFIG_DEBUG_PAGEALLOC /* diff --git a/arch/loongarch/mm/pageattr.c b/arch/loongarch/mm/pageattr.c index f5e910b68229..458f5ae6a89b 100644 --- a/arch/loongarch/mm/pageattr.c +++ b/arch/loongarch/mm/pageattr.c @@ -236,3 +236,4 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)

return __set_memory(addr, 1, set, clear); } +EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm"); diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c index 3f76db3d2769..6db31040cd66 100644 --- a/arch/riscv/mm/pageattr.c +++ b/arch/riscv/mm/pageattr.c @@ -400,6 +400,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)

return __set_memory((unsigned long)page_address(page), nr, set, clear); } +EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");

#ifdef CONFIG_DEBUG_PAGEALLOC static int debug_pagealloc_set_page(pte_t *pte, unsigned long addr, void *data) diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c index 348e759840e7..8ffd9ef09bc6 100644 --- a/arch/s390/mm/pageattr.c +++ b/arch/s390/mm/pageattr.c @@ -413,6 +413,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)

return __set_memory((unsigned long)page_to_virt(page), nr, flags); } +EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");

bool kernel_page_present(struct page *page) { diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 8834c76f91c9..87e9c7d2dcdc 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2661,6 +2661,7 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)

return __set_pages_np(page, nr); } +EXPORT_SYMBOL_FOR_MODULES(set_direct_map_valid_noflush, "kvm");

#ifdef CONFIG_DEBUG_PAGEALLOC void __kernel_map_pages(struct page *page, int numpages, int enable)

Add GUEST_MEMFD_FLAG_NO_DIRECT_MAP flag for KVM_CREATE_GUEST_MEMFD() ioctl. When set, guest_memfd folios will be removed from the direct map after preparation, with direct map entries only restored when the folios are freed.

To ensure these folios do not end up in places where the kernel cannot deal with them, set AS_NO_DIRECT_MAP on the guest_memfd's struct address_space if GUEST_MEMFD_FLAG_NO_DIRECT_MAP is requested.

Add KVM_CAP_GUEST_MEMFD_NO_DIRECT_MAP to let userspace discover whether guest_memfd supports GUEST_MEMFD_FLAG_NO_DIRECT_MAP. Support depends on guest_memfd itself being supported, but also on whether linux supports manipulatomg the direct map at page granularity at all (possible most of the time, outliers being arm64 where its impossible if the direct map has been setup using hugepages, as arm64 cannot break these apart due to break-before-make semantics, and powerpc, which does not select ARCH_HAS_SET_DIRECT_MAP, which also doesn't support guest_memfd anyway though).

Note that this flag causes removal of direct map entries for all guest_memfd folios independent of whether they are "shared" or "private" (although current guest_memfd only supports either all folios in the "shared" state, or all folios in the "private" state if GUEST_MEMFD_FLAG_MMAP is not set). The usecase for removing direct map entries of also the shared parts of guest_memfd are a special type of non-CoCo VM where, host userspace is trusted to have access to all of guest memory, but where Spectre-style transient execution attacks through the host kernel's direct map should still be mitigated. In this setup, KVM retains access to guest memory via userspace mappings of guest_memfd, which are reflected back into KVM's memslots via userspace_addr. This is needed for things like MMIO emulation on x86_64 to work.

Do not perform TLB flushes after direct map manipulations. This is because TLB flushes resulted in a up to 40x elongation of page faults in guest_memfd (scaling with the number of CPU cores), or a 5x elongation of memory population. TLB flushes are not needed for functional correctness (the virt->phys mapping technically stays "correct", the kernel should simply not use it for a while). On the other hand, it means that the desired protection from Spectre-style attacks is not perfect, as an attacker could try to prevent a stale TLB entry from getting evicted, keeping it alive until the page it refers to is used by the guest for some sensitive data, and then targeting it using a spectre-gadget.

Signed-off-by: Patrick Roy roypat@amazon.co.uk --- Documentation/virt/kvm/api.rst | 5 ++++ arch/arm64/include/asm/kvm_host.h | 12 ++++++++ include/linux/kvm_host.h | 7 +++++ include/uapi/linux/kvm.h | 2 ++ virt/kvm/guest_memfd.c | 49 +++++++++++++++++++++++++++---- virt/kvm/kvm_main.c | 5 ++++ 6 files changed, 75 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index c17a87a0a5ac..b52c14d58798 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6418,6 +6418,11 @@ When the capability KVM_CAP_GUEST_MEMFD_MMAP is supported, the 'flags' field supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation enables mmap() and faulting of guest_memfd memory to host userspace.

+When the capability KVM_CAP_GMEM_NO_DIRECT_MAP is supported, the 'flags' field +supports GUEST_MEMFG_FLAG_NO_DIRECT_MAP. Setting this flag makes the guest_memfd +instance behave similarly to memfd_secret, and unmaps the memory backing it from +the kernel's address space after allocation. + When the KVM MMU performs a PFN lookup to service a guest fault and the backing guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be consumed from guest_memfd, regardless of whether it is a shared or a private diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 2f2394cce24e..0bfd8e5fd9de 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -19,6 +19,7 @@ #include <linux/maple_tree.h> #include <linux/percpu.h> #include <linux/psci.h> +#include <linux/set_memory.h> #include <asm/arch_gicv3.h> #include <asm/barrier.h> #include <asm/cpufeature.h> @@ -1706,5 +1707,16 @@ void compute_fgu(struct kvm *kvm, enum fgt_group_id fgt); void get_reg_fixed_bits(struct kvm *kvm, enum vcpu_sysreg reg, u64 *res0, u64 *res1); void check_feature_map(void);

+#ifdef CONFIG_KVM_GUEST_MEMFD +static inline bool kvm_arch_gmem_supports_no_direct_map(void) +{ + /* + * Without FWB, direct map access is needed in kvm_pgtable_stage2_map(), + * as it calls dcache_clean_inval_poc(). + */ + return can_set_direct_map() && cpus_have_final_cap(ARM64_HAS_STAGE2_FWB); +} +#define kvm_arch_gmem_supports_no_direct_map kvm_arch_gmem_supports_no_direct_map +#endif /* CONFIG_KVM_GUEST_MEMFD */

#endif /* __ARM64_KVM_HOST_H__ */ diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 1d0585616aa3..a9468bce55f2 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -36,6 +36,7 @@ #include <linux/rbtree.h> #include <linux/xarray.h> #include <asm/signal.h> +#include <linux/set_memory.h>

#include <linux/kvm.h> #include <linux/kvm_para.h> @@ -731,6 +732,12 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) bool kvm_arch_supports_gmem_mmap(struct kvm *kvm); #endif

+#ifdef CONFIG_KVM_GUEST_MEMFD +#ifndef kvm_arch_gmem_supports_no_direct_map +#define kvm_arch_gmem_supports_no_direct_map can_set_direct_map +#endif +#endif /* CONFIG_KVM_GUEST_MEMFD */ + #ifndef kvm_arch_has_readonly_mem static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) { diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 6efa98a57ec1..33c8e8946019 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -963,6 +963,7 @@ struct kvm_enable_cap { #define KVM_CAP_RISCV_MP_STATE_RESET 242 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243 #define KVM_CAP_GUEST_MEMFD_MMAP 244 +#define KVM_CAP_GUEST_MEMFD_NO_DIRECT_MAP 245

struct kvm_irq_routing_irqchip { __u32 irqchip; @@ -1600,6 +1601,7 @@ struct kvm_memory_attributes {

#define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) #define GUEST_MEMFD_FLAG_MMAP (1ULL << 0) +#define GUEST_MEMFD_FLAG_NO_DIRECT_MAP (1ULL << 1)

struct kvm_create_guest_memfd { __u64 size; diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 81028984ff89..3c64099fc98a 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -4,6 +4,7 @@ #include <linux/kvm_host.h> #include <linux/pagemap.h> #include <linux/anon_inodes.h> +#include <linux/set_memory.h>

#include "kvm_mm.h"

@@ -42,9 +43,24 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo return 0; }

-static inline void kvm_gmem_mark_prepared(struct folio *folio) +static bool kvm_gmem_test_no_direct_map(struct inode *inode) { - folio_mark_uptodate(folio); + return ((unsigned long) inode->i_private) & GUEST_MEMFD_FLAG_NO_DIRECT_MAP; +} + +static inline int kvm_gmem_mark_prepared(struct folio *folio) +{ + struct inode *inode = folio_inode(folio); + int r = 0; + + if (kvm_gmem_test_no_direct_map(inode)) + r = set_direct_map_valid_noflush(folio_page(folio, 0), folio_nr_pages(folio), + false); + + if (!r) + folio_mark_uptodate(folio); + + return r; }

/* @@ -82,7 +98,7 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, index = ALIGN_DOWN(index, 1 << folio_order(folio)); r = __kvm_gmem_prepare_folio(kvm, slot, index, folio); if (!r) - kvm_gmem_mark_prepared(folio); + r = kvm_gmem_mark_prepared(folio);

return r; } @@ -344,8 +360,15 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) }

if (!folio_test_uptodate(folio)) { + int err = 0; + clear_highpage(folio_page(folio, 0)); - kvm_gmem_mark_prepared(folio); + err = kvm_gmem_mark_prepared(folio); + + if (err) { + ret = vmf_error(err); + goto out_folio; + } }

vmf->page = folio_file_page(folio, vmf->pgoff); @@ -436,6 +459,16 @@ static void kvm_gmem_free_folio(struct address_space *mapping, kvm_pfn_t pfn = page_to_pfn(page); int order = folio_order(folio);

+ /* + * Direct map restoration cannot fail, as the only error condition + * for direct map manipulation is failure to allocate page tables + * when splitting huge pages, but this split would have already + * happened in set_direct_map_invalid_noflush() in kvm_gmem_mark_prepared(). + * Thus set_direct_map_valid_noflush() here only updates prot bits. + */ + if (kvm_gmem_test_no_direct_map(mapping->host)) + set_direct_map_valid_noflush(page, folio_nr_pages(folio), true); + kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order)); }

@@ -500,6 +533,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) /* Unmovable mappings are supposed to be marked unevictable as well. */ WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));

+ if (flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP) + mapping_set_no_direct_map(inode->i_mapping); + kvm_get_kvm(kvm); gmem->kvm = kvm; xa_init(&gmem->bindings); @@ -524,6 +560,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) if (kvm_arch_supports_gmem_mmap(kvm)) valid_flags |= GUEST_MEMFD_FLAG_MMAP;

+ if (kvm_arch_gmem_supports_no_direct_map()) + valid_flags |= GUEST_MEMFD_FLAG_NO_DIRECT_MAP; + if (flags & ~valid_flags) return -EINVAL;

@@ -768,7 +807,7 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long p = src ? src + i * PAGE_SIZE : NULL; ret = post_populate(kvm, gfn, pfn, p, max_order, opaque); if (!ret) - kvm_gmem_mark_prepared(folio); + ret = kvm_gmem_mark_prepared(folio);

put_folio_and_exit: folio_put(folio); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 18f29ef93543..b5e702d95230 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -65,6 +65,7 @@ #include <trace/events/kvm.h>

#include <linux/kvm_dirty_ring.h> +#include <linux/set_memory.h>

/* Worst case buffer size needed for holding an integer. */ @@ -4916,6 +4917,10 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) return kvm_supported_mem_attributes(kvm); #endif #ifdef CONFIG_KVM_GUEST_MEMFD + case KVM_CAP_GUEST_MEMFD_NO_DIRECT_MAP: + if (!kvm_arch_gmem_supports_no_direct_map()) + return 0; + fallthrough; case KVM_CAP_GUEST_MEMFD: return 1; case KVM_CAP_GUEST_MEMFD_MMAP:

If guest memory is backed using a VMA that does not allow GUP (e.g. a userspace mapping of guest_memfd when the fd was allocated using KVM_GMEM_NO_DIRECT_MAP), then directly loading the test ELF binary into it via read(2) potentially does not work. To nevertheless support loading binaries in this cases, do the read(2) syscall using a bounce buffer, and then memcpy from the bounce buffer into guest memory.

Signed-off-by: Patrick Roy roypat@amazon.co.uk --- .../testing/selftests/kvm/include/test_util.h | 1 + tools/testing/selftests/kvm/lib/elf.c | 8 +++---- tools/testing/selftests/kvm/lib/io.c | 23 +++++++++++++++++++ 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h index c6ef895fbd9a..0409b7b96c94 100644 --- a/tools/testing/selftests/kvm/include/test_util.h +++ b/tools/testing/selftests/kvm/include/test_util.h @@ -46,6 +46,7 @@ do { \

ssize_t test_write(int fd, const void *buf, size_t count); ssize_t test_read(int fd, void *buf, size_t count); +ssize_t test_read_bounce(int fd, void *buf, size_t count); int test_seq_read(const char *path, char **bufp, size_t *sizep);

void __printf(5, 6) test_assert(bool exp, const char *exp_str, diff --git a/tools/testing/selftests/kvm/lib/elf.c b/tools/testing/selftests/kvm/lib/elf.c index f34d926d9735..e829fbe0a11e 100644 --- a/tools/testing/selftests/kvm/lib/elf.c +++ b/tools/testing/selftests/kvm/lib/elf.c @@ -31,7 +31,7 @@ static void elfhdr_get(const char *filename, Elf64_Ehdr *hdrp) * the real size of the ELF header. */ unsigned char ident[EI_NIDENT]; - test_read(fd, ident, sizeof(ident)); + test_read_bounce(fd, ident, sizeof(ident)); TEST_ASSERT((ident[EI_MAG0] == ELFMAG0) && (ident[EI_MAG1] == ELFMAG1) && (ident[EI_MAG2] == ELFMAG2) && (ident[EI_MAG3] == ELFMAG3), "ELF MAGIC Mismatch,\n" @@ -79,7 +79,7 @@ static void elfhdr_get(const char *filename, Elf64_Ehdr *hdrp) offset_rv = lseek(fd, 0, SEEK_SET); TEST_ASSERT(offset_rv == 0, "Seek to ELF header failed,\n" " rv: %zi expected: %i", offset_rv, 0); - test_read(fd, hdrp, sizeof(*hdrp)); + test_read_bounce(fd, hdrp, sizeof(*hdrp)); TEST_ASSERT(hdrp->e_phentsize == sizeof(Elf64_Phdr), "Unexpected physical header size,\n" " hdrp->e_phentsize: %x\n" @@ -146,7 +146,7 @@ void kvm_vm_elf_load(struct kvm_vm *vm, const char *filename)

/* Read in the program header. */ Elf64_Phdr phdr; - test_read(fd, &phdr, sizeof(phdr)); + test_read_bounce(fd, &phdr, sizeof(phdr));

/* Skip if this header doesn't describe a loadable segment. */ if (phdr.p_type != PT_LOAD) @@ -187,7 +187,7 @@ void kvm_vm_elf_load(struct kvm_vm *vm, const char *filename) " expected: 0x%jx", n1, errno, (intmax_t) offset_rv, (intmax_t) phdr.p_offset); - test_read(fd, addr_gva2hva(vm, phdr.p_vaddr), + test_read_bounce(fd, addr_gva2hva(vm, phdr.p_vaddr), phdr.p_filesz); } } diff --git a/tools/testing/selftests/kvm/lib/io.c b/tools/testing/selftests/kvm/lib/io.c index fedb2a741f0b..74419becc8bc 100644 --- a/tools/testing/selftests/kvm/lib/io.c +++ b/tools/testing/selftests/kvm/lib/io.c @@ -155,3 +155,26 @@ ssize_t test_read(int fd, void *buf, size_t count)

return num_read; } + +/* Test read via intermediary buffer + * + * Same as test_read, except read(2)s happen into a bounce buffer that is memcpy'd + * to buf. For use with buffers that cannot be GUP'd (e.g. guest_memfd VMAs if + * guest_memfd was created with GUEST_MEMFD_FLAG_NO_DIRECT_MAP). + */ +ssize_t test_read_bounce(int fd, void *buf, size_t count) +{ + void *bounce_buffer; + ssize_t num_read; + + TEST_ASSERT(count >= 0, "Unexpected count, count: %li", count); + + bounce_buffer = malloc(count); + TEST_ASSERT(bounce_buffer != NULL, "Failed to allocate bounce buffer"); + + num_read = test_read(fd, bounce_buffer, count); + memcpy(buf, bounce_buffer, num_read); + free(bounce_buffer); + + return num_read; +}

Allow selftests to configure their memslots such that userspace_addr is set to a MAP_SHARED mapping of the guest_memfd that's associated with the memslot. This setup is the configuration for non-CoCo VMs, where all guest memory is backed by a guest_memfd whose folios are all marked shared, but KVM is still able to access guest memory to provide functionality such as MMIO emulation on x86.

Add backing types for normal guest_memfd, as well as direct map removed guest_memfd.

Signed-off-by: Patrick Roy roypat@amazon.co.uk --- .../testing/selftests/kvm/include/kvm_util.h | 18 ++++++ .../testing/selftests/kvm/include/test_util.h | 7 +++ tools/testing/selftests/kvm/lib/kvm_util.c | 63 ++++++++++--------- tools/testing/selftests/kvm/lib/test_util.c | 8 +++ 4 files changed, 66 insertions(+), 30 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h index 23a506d7eca3..5204a0a18a7f 100644 --- a/tools/testing/selftests/kvm/include/kvm_util.h +++ b/tools/testing/selftests/kvm/include/kvm_util.h @@ -635,6 +635,24 @@ static inline bool is_smt_on(void)

void vm_create_irqchip(struct kvm_vm *vm);

+static inline uint32_t backing_src_guest_memfd_flags(enum vm_mem_backing_src_type t) +{ + uint32_t flags = 0; + + switch (t) { + case VM_MEM_SRC_GUEST_MEMFD: + flags |= GUEST_MEMFD_FLAG_MMAP; + fallthrough; + case VM_MEM_SRC_GUEST_MEMFD_NO_DIRECT_MAP: + flags |= GUEST_MEMFD_FLAG_NO_DIRECT_MAP; + break; + default: + break; + } + + return flags; +} + static inline int __vm_create_guest_memfd(struct kvm_vm *vm, uint64_t size, uint64_t flags) { diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h index 0409b7b96c94..a56e53fc7b39 100644 --- a/tools/testing/selftests/kvm/include/test_util.h +++ b/tools/testing/selftests/kvm/include/test_util.h @@ -133,6 +133,8 @@ enum vm_mem_backing_src_type { VM_MEM_SRC_ANONYMOUS_HUGETLB_16GB, VM_MEM_SRC_SHMEM, VM_MEM_SRC_SHARED_HUGETLB, + VM_MEM_SRC_GUEST_MEMFD, + VM_MEM_SRC_GUEST_MEMFD_NO_DIRECT_MAP, NUM_SRC_TYPES, };

@@ -165,6 +167,11 @@ static inline bool backing_src_is_shared(enum vm_mem_backing_src_type t) return vm_mem_backing_src_alias(t)->flag & MAP_SHARED; }

+static inline bool backing_src_is_guest_memfd(enum vm_mem_backing_src_type t) +{ + return t == VM_MEM_SRC_GUEST_MEMFD || t == VM_MEM_SRC_GUEST_MEMFD_NO_DIRECT_MAP; +} + static inline bool backing_src_can_be_huge(enum vm_mem_backing_src_type t) { return t != VM_MEM_SRC_ANONYMOUS && t != VM_MEM_SRC_SHMEM; diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index cc67dfecbf65..a81089f7c83f 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -1060,6 +1060,34 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, alignment = 1; #endif

+ if (guest_memfd < 0) { + if ((flags & KVM_MEM_GUEST_MEMFD) || backing_src_is_guest_memfd(src_type)) { + uint32_t guest_memfd_flags = backing_src_guest_memfd_flags(src_type); + + TEST_ASSERT(!guest_memfd_offset, + "Offset must be zero when creating new guest_memfd"); + guest_memfd = vm_create_guest_memfd(vm, mem_size, guest_memfd_flags); + } + } else { + /* + * Install a unique fd for each memslot so that the fd + * can be closed when the region is deleted without + * needing to track if the fd is owned by the framework + * or by the caller. + */ + guest_memfd = dup(guest_memfd); + TEST_ASSERT(guest_memfd >= 0, __KVM_SYSCALL_ERROR("dup()", guest_memfd)); + } + + if (guest_memfd > 0) { + flags |= KVM_MEM_GUEST_MEMFD; + + region->region.guest_memfd = guest_memfd; + region->region.guest_memfd_offset = guest_memfd_offset; + } else { + region->region.guest_memfd = -1; + } + /* * When using THP mmap is not guaranteed to returned a hugepage aligned * address so we have to pad the mmap. Padding is not needed for HugeTLB @@ -1075,10 +1103,13 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, if (alignment > 1) region->mmap_size += alignment;

- region->fd = -1; - if (backing_src_is_shared(src_type)) + if (backing_src_is_guest_memfd(src_type)) + region->fd = guest_memfd; + else if (backing_src_is_shared(src_type)) region->fd = kvm_memfd_alloc(region->mmap_size, src_type == VM_MEM_SRC_SHARED_HUGETLB); + else + region->fd = -1;

region->mmap_start = mmap(NULL, region->mmap_size, PROT_READ | PROT_WRITE, @@ -1106,34 +1137,6 @@ void vm_mem_add(struct kvm_vm *vm, enum vm_mem_backing_src_type src_type, }

region->backing_src_type = src_type; - - if (guest_memfd < 0) { - if (flags & KVM_MEM_GUEST_MEMFD) { - uint32_t guest_memfd_flags = 0; - TEST_ASSERT(!guest_memfd_offset, - "Offset must be zero when creating new guest_memfd"); - guest_memfd = vm_create_guest_memfd(vm, mem_size, guest_memfd_flags); - } - } else { - /* - * Install a unique fd for each memslot so that the fd - * can be closed when the region is deleted without - * needing to track if the fd is owned by the framework - * or by the caller. - */ - guest_memfd = dup(guest_memfd); - TEST_ASSERT(guest_memfd >= 0, __KVM_SYSCALL_ERROR("dup()", guest_memfd)); - } - - if (guest_memfd > 0) { - flags |= KVM_MEM_GUEST_MEMFD; - - region->region.guest_memfd = guest_memfd; - region->region.guest_memfd_offset = guest_memfd_offset; - } else { - region->region.guest_memfd = -1; - } - region->unused_phy_pages = sparsebit_alloc(); if (vm_arch_has_protected_memory(vm)) region->protected_phy_pages = sparsebit_alloc(); diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c index 03eb99af9b8d..b2baee680083 100644 --- a/tools/testing/selftests/kvm/lib/test_util.c +++ b/tools/testing/selftests/kvm/lib/test_util.c @@ -299,6 +299,14 @@ const struct vm_mem_backing_src_alias *vm_mem_backing_src_alias(uint32_t i) */ .flag = MAP_SHARED, }, + [VM_MEM_SRC_GUEST_MEMFD] = { + .name = "guest_memfd", + .flag = MAP_SHARED, + }, + [VM_MEM_SRC_GUEST_MEMFD_NO_DIRECT_MAP] = { + .name = "guest_memfd_no_direct_map", + .flag = MAP_SHARED, + } }; _Static_assert(ARRAY_SIZE(aliases) == NUM_SRC_TYPES, "Missing new backing src types?");

Extend mem conversion selftests to cover the scenario that the guest can fault in and write gmem-backed guest memory even if its direct map removed. Also cover the new flag in guest_memfd_test.c tests.

Signed-off-by: Patrick Roy roypat@amazon.co.uk --- tools/testing/selftests/kvm/guest_memfd_test.c | 2 ++ .../selftests/kvm/x86/private_mem_conversions_test.c | 7 ++++--- 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c index b3ca6737f304..1187438b6831 100644 --- a/tools/testing/selftests/kvm/guest_memfd_test.c +++ b/tools/testing/selftests/kvm/guest_memfd_test.c @@ -275,6 +275,8 @@ static void test_guest_memfd(unsigned long vm_type)

if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP)) flags |= GUEST_MEMFD_FLAG_MMAP; + if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_NO_DIRECT_MAP)) + flags |= GUEST_MEMFD_FLAG_NO_DIRECT_MAP;

test_create_guest_memfd_multiple(vm); test_create_guest_memfd_invalid_sizes(vm, flags, page_size); diff --git a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c index 82a8d88b5338..8427d9fbdb23 100644 --- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c +++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c @@ -367,7 +367,7 @@ static void *__test_mem_conversions(void *__vcpu) }

static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t nr_vcpus, - uint32_t nr_memslots) + uint32_t nr_memslots, uint64_t gmem_flags) { /* * Allocate enough memory so that each vCPU's chunk of memory can be @@ -394,7 +394,7 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t

vm_enable_cap(vm, KVM_CAP_EXIT_HYPERCALL, (1 << KVM_HC_MAP_GPA_RANGE));

- memfd = vm_create_guest_memfd(vm, memfd_size, 0); + memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);

for (i = 0; i < nr_memslots; i++) vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i, @@ -477,7 +477,8 @@ int main(int argc, char *argv[]) } }

- test_mem_conversions(src_type, nr_vcpus, nr_memslots); + test_mem_conversions(src_type, nr_vcpus, nr_memslots, 0); + test_mem_conversions(src_type, nr_vcpus, nr_memslots, GUEST_MEMFD_FLAG_NO_DIRECT_MAP);

return 0; }