The patch titled
Subject: mm/page_table_check: check entries at pmd levels
has been added to the -mm tree. Its filename is
mm-page_table_check-check-entries-at-pmd-levels.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-page_table_check-check-entries-at-pmd-levels.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_table_check-check-entries-at-pmd-levels.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: mm/page_table_check: check entries at pmd levels
syzbot detected a case where the page table counters were not properly
updated.
syzkaller login: ------------[ cut here ]------------
kernel BUG at mm/page_table_check.c:162!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 3099 Comm: pasha Not tainted 5.16.0+ #48
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO4
RIP: 0010:__page_table_check_zero+0x159/0x1a0
Code: 7d 3a b2 ff 45 39 f5 74 2a e8 43 38 b2 ff 4d 85 e4 01
RSP: 0018:ffff888010667418 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000
RDX: ffff88800cea8680 RSI: ffffffff81becaf9 RDI: 0000000003
RBP: ffff888010667450 R08: 0000000000000001 R09: 0000000000
R10: ffffffff81becaab R11: 0000000000000001 R12: ffff888008
R13: 0000000000000001 R14: 0000000000000200 R15: dffffc0000
FS: 0000000000000000(0000) GS:ffff888035e00000(0000) knlG0
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd875cad00 CR3: 00000000094ce000 CR4: 0000000000
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000
Call Trace:
<TASK>
free_pcp_prepare+0x3be/0xaa0
free_unref_page+0x1c/0x650
? trace_hardirqs_on+0x6a/0x1d0
free_compound_page+0xec/0x130
free_transhuge_page+0x1be/0x260
__put_compound_page+0x90/0xd0
release_pages+0x54c/0x1060
? filemap_remove_folio+0x161/0x210
? lock_downgrade+0x720/0x720
? __put_page+0x150/0x150
? filemap_free_folio+0x164/0x350
__pagevec_release+0x7c/0x110
shmem_undo_range+0x85e/0x1250
...
The repro involved having a huge page that is split due to uprobe event
temporarily replacing one of the pages in the huge page. Later the huge
page was combined again, but the counters were off, as the PTE level was
not properly updated.
Make sure that when PMD is cleared and prior to freeing the level the PTEs
are updated.
Link: https://lkml.kernel.org/r/20220126183637.1840960-5-pasha.tatashin@xxxxxxxxxx
Fixes: df4e817b7108 ("mm: page table check")
Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page_table_check.h | 18 ++++++++++++++++++
mm/khugepaged.c | 3 +++
mm/page_table_check.c | 21 +++++++++++++++++++++
3 files changed, 42 insertions(+)
--- a/include/linux/page_table_check.h~mm-page_table_check-check-entries-at-pmd-levels
+++ a/include/linux/page_table_check.h
@@ -26,6 +26,8 @@ void __page_table_check_pmd_set(struct m
pmd_t *pmdp, pmd_t pmd);
void __page_table_check_pud_set(struct mm_struct *mm, unsigned long addr,
pud_t *pudp, pud_t pud);
+void __page_table_check_pmd_clear_full(struct mm_struct *mm, unsigned long addr,
+ pmd_t pmd);
static inline void page_table_check_alloc(struct page *page, unsigned int order)
{
@@ -100,6 +102,16 @@ static inline void page_table_check_pud_
__page_table_check_pud_set(mm, addr, pudp, pud);
}
+static inline void page_table_check_pmd_clear_full(struct mm_struct *mm,
+ unsigned long addr,
+ pmd_t pmd)
+{
+ if (static_branch_likely(&page_table_check_disabled))
+ return;
+
+ __page_table_check_pmd_clear_full(mm, addr, pmd);
+}
+
#else
static inline void page_table_check_alloc(struct page *page, unsigned int order)
@@ -143,5 +155,11 @@ static inline void page_table_check_pud_
{
}
+static inline void page_table_check_pmd_clear_full(struct mm_struct *mm,
+ unsigned long addr,
+ pmd_t pmd)
+{
+}
+
#endif /* CONFIG_PAGE_TABLE_CHECK */
#endif /* __LINUX_PAGE_TABLE_CHECK_H */
--- a/mm/khugepaged.c~mm-page_table_check-check-entries-at-pmd-levels
+++ a/mm/khugepaged.c
@@ -16,6 +16,7 @@
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
#include <linux/page_idle.h>
+#include <linux/page_table_check.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
@@ -1422,10 +1423,12 @@ static void collapse_and_free_pmd(struct
spinlock_t *ptl;
pmd_t pmd;
+ mmap_assert_write_locked(mm);
ptl = pmd_lock(vma->vm_mm, pmdp);
pmd = pmdp_collapse_flush(vma, addr, pmdp);
spin_unlock(ptl);
mm_dec_nr_ptes(mm);
+ page_table_check_pmd_clear_full(mm, addr, pmd);
pte_free(mm, pmd_pgtable(pmd));
}
--- a/mm/page_table_check.c~mm-page_table_check-check-entries-at-pmd-levels
+++ a/mm/page_table_check.c
@@ -247,3 +247,24 @@ void __page_table_check_pud_set(struct m
}
}
EXPORT_SYMBOL(__page_table_check_pud_set);
+
+void __page_table_check_pmd_clear_full(struct mm_struct *mm, unsigned long addr,
+ pmd_t pmd)
+{
+ if (&init_mm == mm)
+ return;
+
+ if (!pmd_bad(pmd) && !pmd_leaf(pmd)) {
+ pte_t *ptep = pte_offset_map(&pmd, addr);
+ unsigned long i;
+
+ pte_unmap(ptep);
+ for (i = 0; i < PTRS_PER_PTE; i++) {
+ __page_table_check_pte_clear(mm, addr, *ptep);
+ addr += PAGE_SIZE;
+ ptep++;
+ }
+ } else {
+ __page_table_check_pmd_clear(mm, addr, pmd);
+ }
+}
_
Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are
mm-debug_vm_pgtable-remove-pte-entry-from-the-page-table.patch
mm-page_table_check-use-unsigned-long-for-page-counters-and-cleanup.patch
mm-khugepaged-unify-collapse-pmd-clear-flush-and-free.patch
mm-page_table_check-check-entries-at-pmd-levels.patch
