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| author | Hongchen Zhang <zhanghongchen@loongson.cn> | 2026-06-25 13:03:49 +0800 |
|---|---|---|
| committer | Huacai Chen <chenhuacai@loongson.cn> | 2026-06-25 13:03:49 +0800 |
| commit | 018e9828eb523c638fa3d9bdf0fd4956b74555b2 (patch) | |
| tree | dcdbc019a5b4bfa5feb792ed6dc7ffac507ff227 /arch | |
| parent | d4e58d2c21d94282d512979dfa7e045c5034b0be (diff) | |
| download | ath-018e9828eb523c638fa3d9bdf0fd4956b74555b2.tar.gz | |
LoongArch: Fix missing dirty page tracking in {pte,pmd}_wrprotect()
When hardware page table walker (PTW) is enabled on LoongArch, the CPU
may set _PAGE_DIRTY directly in the page table entry during a write TLB
miss, without going through the software TLB store handler. The software
TLB store handler (tlbex.S:254) sets both _PAGE_DIRTY and_PAGE_MODIFIED
together:
ori t0, t0, (_PAGE_VALID | _PAGE_DIRTY | _PAGE_MODIFIED)
Since hardware PTW only sets _PAGE_DIRTY, the software-only bit, i.e.
_PAGE_MODIFIED is left unchanged. This creates a window where a PTE has
_PAGE_DIRTY set (hardware knows the page is dirty) but _PAGE_MODIFIED
clear (software is unaware).
When fork()/clone() triggers copy-on-write, __copy_present_ptes() calls
pte_wrprotect(), which unconditionally clears both the _PAGE_WRITE and
_PAGE_DIRTY bits:
pte_val(pte) &= ~(_PAGE_WRITE | _PAGE_DIRTY);
Since _PAGE_MODIFIED was never set, the dirtiness information is lost
completely. Subsequently, when memory pressure triggers page reclaim,
page_mkclean() / try_to_unmap() sees the page as clean (i.e. pte_dirty()
returns false) and the page may be freed without writeback, causing data
corruption.
Fix this by propagating the _PAGE_DIRTY bit to the _PAGE_MODIFIED bit in
both pte_wrprotect() and pmd_wrprotect() before clearing writeable bits:
if (pte_val(pte) & _PAGE_DIRTY)
pte_val(pte) |= _PAGE_MODIFIED;
The pmd_wrprotect() fix handles the CONFIG_TRANSPARENT_HUGEPAGE case,
where pmd entries need the same treatment.
This ensures the software dirty tracking bit (checked by pte_dirty() and
pmd_dirty(), which read both the _PAGE_DIRTY and _PAGE_MODIFIED bits) is
preserved across fork COW write-protection.
The issue was found by the LTP madvise09 test case, which exercises page
reclaim after "madvise(MADV_FREE), write and fork" operation sequence on
private anonymous mappings.
Cc: stable@vger.kernel.org
Fixes: 09cfefb7fa70 ("LoongArch: Add memory management")
Co-developed-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/loongarch/include/asm/pgtable.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h index 2a0b63ae421f4..223528c04d739 100644 --- a/arch/loongarch/include/asm/pgtable.h +++ b/arch/loongarch/include/asm/pgtable.h @@ -429,6 +429,8 @@ static inline pte_t pte_mkwrite_novma(pte_t pte) static inline pte_t pte_wrprotect(pte_t pte) { + if (pte_val(pte) & _PAGE_DIRTY) + pte_val(pte) |= _PAGE_MODIFIED; pte_val(pte) &= ~(_PAGE_WRITE | _PAGE_DIRTY); return pte; } @@ -535,6 +537,8 @@ static inline pmd_t pmd_mkwrite_novma(pmd_t pmd) static inline pmd_t pmd_wrprotect(pmd_t pmd) { + if (pmd_val(pmd) & _PAGE_DIRTY) + pmd_val(pmd) |= _PAGE_MODIFIED; pmd_val(pmd) &= ~(_PAGE_WRITE | _PAGE_DIRTY); return pmd; } |