2022-11-21 06:58:50

by Huacai Chen

Subject: [PATCH] LoongArch: Set _PAGE_DIRTY only if _PAGE_MODIFIED is set in {pmd,pte}_mkwrite()

Set _PAGE_DIRTY only if _PAGE_MODIFIED is set in {pmd,pte}_mkwrite().
Otherwise, _PAGE_DIRTY silences the TLB modify exception and make us
have no chance to mark a pmd/pte dirty (_PAGE_MODIFIED) for software.

Signed-off-by: Huacai Chen <[email protected]>
---
arch/loongarch/include/asm/pgtable.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index debbe116f105..aa0e0e0d4ee5 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -357,7 +357,9 @@ static inline pte_t pte_mkdirty(pte_t pte)

static inline pte_t pte_mkwrite(pte_t pte)
{
- pte_val(pte) |= (_PAGE_WRITE | _PAGE_DIRTY);
+ pte_val(pte) |= _PAGE_WRITE;
+ if (pte_val(pte) & _PAGE_MODIFIED)
+ pte_val(pte) |= _PAGE_DIRTY;
return pte;
}

@@ -457,7 +459,9 @@ static inline int pmd_write(pmd_t pmd)

static inline pmd_t pmd_mkwrite(pmd_t pmd)
{
- pmd_val(pmd) |= (_PAGE_WRITE | _PAGE_DIRTY);
+ pmd_val(pmd) |= _PAGE_WRITE;
+ if (pmd_val(pmd) & _PAGE_MODIFIED)
+ pmd_val(pmd) |= _PAGE_DIRTY;
return pmd;
}

--
2.31.1

2022-11-21 10:35:55

by Guo Ren

Subject: Re: [PATCH] LoongArch: Set _PAGE_DIRTY only if _PAGE_MODIFIED is set in {pmd,pte}_mkwrite()

On Mon, Nov 21, 2022 at 2:51 PM Huacai Chen <[email protected]> wrote:
>
> Set _PAGE_DIRTY only if _PAGE_MODIFIED is set in {pmd,pte}_mkwrite().
> Otherwise, _PAGE_DIRTY silences the TLB modify exception and make us
> have no chance to mark a pmd/pte dirty (_PAGE_MODIFIED) for software.
Yes, the "VALID/DIRTY" is a bad hardware pgtable-bit design. It
caused the software to waste more bits in PTE. We need hardware
P/R/W/A/D definitions. It seems from MIPS in history, C-SKY also
follows that :P.

Reviewed-by: Guo Ren <[email protected]>

>
> Signed-off-by: Huacai Chen <[email protected]>
> ---
> arch/loongarch/include/asm/pgtable.h | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index debbe116f105..aa0e0e0d4ee5 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -357,7 +357,9 @@ static inline pte_t pte_mkdirty(pte_t pte)
>
> static inline pte_t pte_mkwrite(pte_t pte)
> {
> - pte_val(pte) |= (_PAGE_WRITE | _PAGE_DIRTY);
> + pte_val(pte) |= _PAGE_WRITE;
> + if (pte_val(pte) & _PAGE_MODIFIED)
> + pte_val(pte) |= _PAGE_DIRTY;
> return pte;
> }
>
> @@ -457,7 +459,9 @@ static inline int pmd_write(pmd_t pmd)
>
> static inline pmd_t pmd_mkwrite(pmd_t pmd)
> {
> - pmd_val(pmd) |= (_PAGE_WRITE | _PAGE_DIRTY);
> + pmd_val(pmd) |= _PAGE_WRITE;
> + if (pmd_val(pmd) & _PAGE_MODIFIED)
> + pmd_val(pmd) |= _PAGE_DIRTY;
> return pmd;
> }
>
> --
> 2.31.1
>


--
Best Regards
Guo Ren