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LoongArch: Set _PAGE_DIRTY only if _PAGE_WRITE is set in {pmd,pte}_mkdirty() 

Now {pmd,pte}_mkdirty() set _PAGE_DIRTY bit unconditionally, this causes
random segmentation fault after commit 0ccf7f168e ("mm/thp: carry
over dirty bit when thp splits on pmd").

The reason is: when fork(), parent process use pmd_wrprotect() to clear
huge page's _PAGE_WRITE and _PAGE_DIRTY (for COW); then pte_mkdirty() set
_PAGE_DIRTY as well as _PAGE_MODIFIED while splitting dirty huge pages;
once _PAGE_DIRTY is set, there will be no tlb modify exception so the COW
machanism fails; and at last memory corruption occurred between parent
and child processes.

So, we should set _PAGE_DIRTY only when _PAGE_WRITE is set in {pmd,pte}_
mkdirty().

Cc: stable@vger.kernel.org
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Huacai Chen 2022-11-21 19:02:57 +08:00
parent e428e96135
commit bf2f34a506
1 changed files with 6 additions and 2 deletions
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8
arch/loongarch/include/asm/pgtable.h
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@ -349,7 +349,9 @@ static inline pte_t pte_mkclean(pte_t pte)
static inline pte_t pte_mkdirty(pte_t pte)
{
pte_val(pte) |= (_PAGE_DIRTY | _PAGE_MODIFIED);
pte_val(pte) |= _PAGE_MODIFIED;
if (pte_val(pte) & _PAGE_WRITE)
pte_val(pte) |= _PAGE_DIRTY;
return pte;
}
@ -478,7 +480,9 @@ static inline pmd_t pmd_mkclean(pmd_t pmd)
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
pmd_val(pmd) |= (_PAGE_DIRTY | _PAGE_MODIFIED);
pmd_val(pmd) |= _PAGE_MODIFIED;
if (pmd_val(pmd) & _PAGE_WRITE)
pmd_val(pmd) |= _PAGE_DIRTY;
return pmd;
}