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From: Minchan Kim <minchan@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org, kernel-team@android.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	Yu Zhao <yuzhao@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/6] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()
Date: Fri, 20 Nov 2020 09:09:03 -0800	[thread overview]
Message-ID: <20201120170903.GC3377168@google.com> (raw)
In-Reply-To: <20201120143557.6715-3-will@kernel.org>

On Fri, Nov 20, 2020 at 02:35:53PM +0000, Will Deacon wrote:
> 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@vger.kernel.org>

It this stable material if it would be a problem once ARM64 supports
softdirty in future?

> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  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 1bdf51f01e73..a155551863c9 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -162,13 +162,6 @@ static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
>  	return pmd;
>  }
>  
> -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));
> @@ -194,6 +187,20 @@ 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));
> @@ -843,12 +850,6 @@ 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));
> -- 
> 2.29.2.454.gaff20da3a2-goog
> 

  reply	other threads:[~2020-11-20 17:09 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20201120143557.6715-1-will@kernel.org>
2020-11-20 14:35 ` [PATCH 1/6] arm64: pgtable: Fix pte_accessible() Will Deacon
2020-11-20 16:03   ` Minchan Kim
2020-11-20 19:53   ` Yu Zhao
2020-11-23 13:27   ` Catalin Marinas
2020-11-24 10:02   ` Anshuman Khandual
2020-11-20 14:35 ` [PATCH 2/6] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect() Will Deacon
2020-11-20 17:09   ` Minchan Kim [this message]
2020-11-23 14:31     ` Catalin Marinas
2020-11-23 14:22   ` Catalin Marinas

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