ACK: [SRU][B/aws, F/aws, G/aws, H/aws][PATCH 1/1] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()

[Kamal Mostafa]

LGTM -- thanks, Andrea.
 
Acked-by: Kamal Mostafa <kamal at canonical.com>

 -Kamal

On Thu, Dec 17, 2020 at 10:42:33AM +0100, Andrea Righi wrote:
> From: Will Deacon <will at kernel.org>
> 
> BugLink: https://bugs.launchpad.net/bugs/1908503
> 
> With hardware dirty bit management, calling pte_wrprotect() on a writable,
> dirty PTE will lose the dirty state and return a read-only, clean entry.
> 
> Move the logic from ptep_set_wrprotect() into pte_wrprotect() to ensure that
> the dirty bit is preserved for writable entries, as this is required for
> soft-dirty bit management if we enable it in the future.
> 
> Cc: <stable at vger.kernel.org>
> Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
> Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
> Link: https://lore.kernel.org/r/20201120143557.6715-3-will@kernel.org
> Signed-off-by: Will Deacon <will at kernel.org>
> (backported from commit ff1712f953e27f0b0718762ec17d0adb15c9fd0b)
> Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
> ---
>  arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 41dd4b1f0ccb..32e62b60989c 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -135,13 +135,6 @@ static inline pte_t set_pte_bit(pte_t pte, pgprot_t prot)
>  	return pte;
>  }
>  
> -static inline pte_t pte_wrprotect(pte_t pte)
> -{
> -	pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
> -	pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
> -	return pte;
> -}
> -
>  static inline pte_t pte_mkwrite(pte_t pte)
>  {
>  	pte = set_pte_bit(pte, __pgprot(PTE_WRITE));
> @@ -167,6 +160,20 @@ static inline pte_t pte_mkdirty(pte_t pte)
>  	return pte;
>  }
>  
> +static inline pte_t pte_wrprotect(pte_t pte)
> +{
> +	/*
> +	 * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
> +	 * clear), set the PTE_DIRTY bit.
> +	 */
> +	if (pte_hw_dirty(pte))
> +		pte = pte_mkdirty(pte);
> +
> +	pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
> +	pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
> +	return pte;
> +}
> +
>  static inline pte_t pte_mkold(pte_t pte)
>  {
>  	return clear_pte_bit(pte, __pgprot(PTE_AF));
> @@ -782,12 +789,6 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
>  	pte = READ_ONCE(*ptep);
>  	do {
>  		old_pte = pte;
> -		/*
> -		 * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
> -		 * clear), set the PTE_DIRTY bit.
> -		 */
> -		if (pte_hw_dirty(pte))
> -			pte = pte_mkdirty(pte);
>  		pte = pte_wrprotect(pte);
>  		pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
>  					       pte_val(old_pte), pte_val(pte));
> -- 
> 2.29.2
> 
> 
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