2023-07-13 07:23:19

by Anshuman Khandual

Subject: [PATCH] arm64/mm: Set only the PTE_DIRTY bit while preserving the HW dirty state

pte_mkdirty() creates dirty states both in SW and HW bits, which is really
not required, either in pte_wrprotect() or pte_modify() for preserving the
HW dirty state. Because pte_mkdirty() sets PTE_DIRTY and clears PTE_RDONLY
as pte_write() always evaluates to be true - otherwise pte_hw_dirty() will
not test out in the first place. Clearing PTE_RDONLY again is not required
here because the pte is already in pte_hw_dirty() but might soon loose its
dirty state thus requiring preservation in SW dirty bit i.e PTE_DIRTY.

Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Anshuman Khandual <[email protected]>
---
This applies on v6.5-rc1

arch/arm64/include/asm/pgtable.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0bd18de9fd97..171d6d7f8087 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -212,7 +212,7 @@ static inline pte_t pte_wrprotect(pte_t pte)
* clear), set the PTE_DIRTY bit.
*/
if (pte_hw_dirty(pte))
- pte = pte_mkdirty(pte);
+ pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));

pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
@@ -823,7 +823,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
PTE_ATTRINDX_MASK;
/* preserve the hardware dirty information */
if (pte_hw_dirty(pte))
- pte = pte_mkdirty(pte);
+ pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
+
pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
return pte;
}
--
2.30.2

2023-07-13 12:30:42

by David Hildenbrand

Subject: Re: [PATCH] arm64/mm: Set only the PTE_DIRTY bit while preserving the HW dirty state

On 13.07.23 09:15, Anshuman Khandual wrote:
> pte_mkdirty() creates dirty states both in SW and HW bits, which is really
> not required, either in pte_wrprotect() or pte_modify() for preserving the
> HW dirty state. Because pte_mkdirty() sets PTE_DIRTY and clears PTE_RDONLY
> as pte_write() always evaluates to be true - otherwise pte_hw_dirty() will
> not test out in the first place. Clearing PTE_RDONLY again is not required
> here because the pte is already in pte_hw_dirty() but might soon loose its
> dirty state thus requiring preservation in SW dirty bit i.e PTE_DIRTY.
>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Anshuman Khandual <[email protected]>
> ---
> This applies on v6.5-rc1
>
> arch/arm64/include/asm/pgtable.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 0bd18de9fd97..171d6d7f8087 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -212,7 +212,7 @@ static inline pte_t pte_wrprotect(pte_t pte)
> * clear), set the PTE_DIRTY bit.
> */
> if (pte_hw_dirty(pte))
> - pte = pte_mkdirty(pte);
> + pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
>
> pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
> pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
> @@ -823,7 +823,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
> PTE_ATTRINDX_MASK;
> /* preserve the hardware dirty information */
> if (pte_hw_dirty(pte))
> - pte = pte_mkdirty(pte);
> + pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
> +
> pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
> return pte;
> }

Reviewed-by: David Hildenbrand <[email protected]>

--
Cheers,

David / dhildenb

2023-07-21 18:45:31

by Catalin Marinas

Subject: Re: [PATCH] arm64/mm: Set only the PTE_DIRTY bit while preserving the HW dirty state

On Thu, Jul 13, 2023 at 12:45:18PM +0530, Anshuman Khandual wrote:
> pte_mkdirty() creates dirty states both in SW and HW bits, which is really
> not required, either in pte_wrprotect() or pte_modify() for preserving the
> HW dirty state. Because pte_mkdirty() sets PTE_DIRTY and clears PTE_RDONLY
> as pte_write() always evaluates to be true - otherwise pte_hw_dirty() will
> not test out in the first place. Clearing PTE_RDONLY again is not required
> here because the pte is already in pte_hw_dirty() but might soon loose its
> dirty state thus requiring preservation in SW dirty bit i.e PTE_DIRTY.
>
> Cc: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Anshuman Khandual <[email protected]>

Acked-by: Catalin Marinas <[email protected]>

2023-07-27 13:04:48

by Will Deacon

Subject: Re: [PATCH] arm64/mm: Set only the PTE_DIRTY bit while preserving the HW dirty state

On Thu, 13 Jul 2023 12:45:18 +0530, Anshuman Khandual wrote:
> pte_mkdirty() creates dirty states both in SW and HW bits, which is really
> not required, either in pte_wrprotect() or pte_modify() for preserving the
> HW dirty state. Because pte_mkdirty() sets PTE_DIRTY and clears PTE_RDONLY
> as pte_write() always evaluates to be true - otherwise pte_hw_dirty() will
> not test out in the first place. Clearing PTE_RDONLY again is not required
> here because the pte is already in pte_hw_dirty() but might soon loose its
> dirty state thus requiring preservation in SW dirty bit i.e PTE_DIRTY.
>
> [...]

Applied to arm64 (for-next/mm), thanks!

[1/1] arm64/mm: Set only the PTE_DIRTY bit while preserving the HW dirty state
https://git.kernel.org/arm64/c/6477c3886ae1

Cheers,
--
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev