The patch titled Subject: mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd() has been added to the -mm mm-new branch. Its filename is mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Anshuman Khandual anshuman.khandual@arm.com Subject: mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd() Date: Fri, 20 Jun 2025 10:54:27 +0530

Memory hot remove unmaps and tears down various kernel page table regions as required. The ptdump code can race with concurrent modifications of the kernel page tables. When leaf entries are modified concurrently, the dump code may log stale or inconsistent information for a VA range, but this is otherwise not harmful.

But when intermediate levels of kernel page table are freed, the dump code will continue to use memory that has been freed and potentially reallocated for another purpose. In such cases, the ptdump code may dereference bogus addresses, leading to a number of potential problems.

To avoid the above mentioned race condition, platforms such as arm64, riscv and s390 take memory hotplug lock, while dumping kernel page table via the sysfs interface /sys/kernel/debug/kernel_page_tables.

Similar race condition exists while checking for pages that might have been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in turn calls ptdump_check_wx(). Instead of solving this race condition again, let's just move the memory hotplug lock inside generic ptdump_check_wx() which will benefit both the scenarios.

Drop get_online_mems() and put_online_mems() combination from all existing platform ptdump code paths.

Link: https://lkml.kernel.org/r/20250620052427.2092093-1-anshuman.khandual@arm.com Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove") Signed-off-by: Anshuman Khandual anshuman.khandual@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Cc: Ryan Roberts ryan.roberts@arm.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Alexander Gordeev agordeev@linux.ibm.com Cc: Gerald Schaefer gerald.schaefer@linux.ibm.com Cc: Heiko Carstens hca@linux.ibm.com Cc: Vasily Gorbik gor@linux.ibm.com Cc: Christian Borntraeger borntraeger@linux.ibm.com Cc: Sven Schnelle svens@linux.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/arm64/mm/ptdump_debugfs.c | 3 --- arch/riscv/mm/ptdump.c | 3 --- arch/s390/mm/dump_pagetables.c | 2 -- mm/ptdump.c | 2 ++ 4 files changed, 2 insertions(+), 8 deletions(-)

--- a/arch/arm64/mm/ptdump_debugfs.c~mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd +++ a/arch/arm64/mm/ptdump_debugfs.c @@ -1,6 +1,5 @@ // SPDX-License-Identifier: GPL-2.0 #include <linux/debugfs.h> -#include <linux/memory_hotplug.h> #include <linux/seq_file.h>

#include <asm/ptdump.h> @@ -9,9 +8,7 @@ static int ptdump_show(struct seq_file * { struct ptdump_info *info = m->private;

- get_online_mems(); ptdump_walk(m, info); - put_online_mems(); return 0; } DEFINE_SHOW_ATTRIBUTE(ptdump); --- a/arch/riscv/mm/ptdump.c~mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd +++ a/arch/riscv/mm/ptdump.c @@ -6,7 +6,6 @@ #include <linux/efi.h> #include <linux/init.h> #include <linux/debugfs.h> -#include <linux/memory_hotplug.h> #include <linux/seq_file.h> #include <linux/ptdump.h>

@@ -413,9 +412,7 @@ bool ptdump_check_wx(void)

static int ptdump_show(struct seq_file *m, void *v) { - get_online_mems(); ptdump_walk(m, m->private); - put_online_mems();

return 0; } --- a/arch/s390/mm/dump_pagetables.c~mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd +++ a/arch/s390/mm/dump_pagetables.c @@ -247,11 +247,9 @@ static int ptdump_show(struct seq_file * .marker = markers, };

- get_online_mems(); mutex_lock(&cpa_mutex); ptdump_walk_pgd(&st.ptdump, &init_mm, NULL); mutex_unlock(&cpa_mutex); - put_online_mems(); return 0; } DEFINE_SHOW_ATTRIBUTE(ptdump); --- a/mm/ptdump.c~mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd +++ a/mm/ptdump.c @@ -176,6 +176,7 @@ void ptdump_walk_pgd(struct ptdump_state { const struct ptdump_range *range = st->range;

+ get_online_mems(); mmap_write_lock(mm); while (range->start != range->end) { walk_page_range_debug(mm, range->start, range->end, @@ -183,6 +184,7 @@ void ptdump_walk_pgd(struct ptdump_state range++; } mmap_write_unlock(mm); + put_online_mems();

/* Flush out the last page */ st->note_page_flush(st); _

Patches currently in -mm which might be from anshuman.khandual@arm.com are

mm-ptdump-take-the-memory-hotplug-lock-inside-ptdump_walk_pgd.patch