Re: [PATCH] MIPS: fix pmd_mkinvalid

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On 2022/5/31 下午11:40, Jiaxun Yang wrote:


在 2022/5/31 5:36, Hongchen Zhang 写道:
pmd_mkinvalid should not clear dirty flag,otherwise the pmd
dirty flag,it's ok to just clear _PAGE_VALID.
Hi Hongcheng,

Sorry, what is meant by "otherwise the pmd dirty flag"? Could you please
elaborate?
In my humble opinion _PAGE_PRESENT must be cleared in mkinvalid as it
nolonger present here. And thus it lose the dirty status.

Thanks
- Jiaxun

Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
---
  arch/mips/include/asm/pgtable.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 374c632..d30a186 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -698,7 +698,7 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
  static inline pmd_t pmd_mkinvalid(pmd_t pmd)
  {
-    pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
+    pmd_val(pmd) &= ~_PAGE_VALID;
      return pmd;
  }
Hi Jiaxun,

Refer to [ https://lkml.org/lkml/2018/10/17/231 ],Andrea said "
The clear of the real present bit during pmd (virtual) splitting is
done with pmdp_invalidate, that is created specifically to keeps
pmd_trans_huge=true, pmd_present=true despite the present bit is not
set. ". So it's wrong to clear _PAGE_PRESENT,because this will make pmd_present=false.

On the other hand, There is no need to clear dirty flag too.

Thanks.




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