6.6-stable review patch. If anyone has any objections, please let me know.
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From: Anshuman Khandual anshuman.khandual@arm.com
commit 59305202c67fea50378dcad0cc199dbc13a0e99a upstream.
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 Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Dev Jain dev.jain@arm.com Acked-by: Alexander Gordeev agordeev@linux.ibm.com [s390] 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 Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/mm/ptdump_debugfs.c | 3 --- arch/s390/mm/dump_pagetables.c | 2 -- mm/ptdump.c | 2 ++ 3 files changed, 2 insertions(+), 5 deletions(-)
--- a/arch/arm64/mm/ptdump_debugfs.c +++ b/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/s390/mm/dump_pagetables.c +++ b/arch/s390/mm/dump_pagetables.c @@ -249,11 +249,9 @@ static int ptdump_show(struct seq_file * .marker = address_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 +++ b/mm/ptdump.c @@ -152,6 +152,7 @@ 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_novma(mm, range->start, range->end, @@ -159,6 +160,7 @@ void ptdump_walk_pgd(struct ptdump_state range++; } mmap_write_unlock(mm); + put_online_mems();
/* Flush out the last page */ st->note_page(st, 0, -1, 0);