linux-kernel - Re: [PATCH 2/2] arm64: mm: Always make sw-dirty PTEs hw-dirty in pte

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Message-ID: <1ccb1e57-1aef-4797-b6d2-ab59efa488db@arm.com>
Date:   Wed, 6 Dec 2023 10:26:46 +0000
From:   Ryan Roberts <ryan.roberts@....com>
To:     James Houghton <jthoughton@...gle.com>,
        Steve Capper <steve.capper@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: mm: Always make sw-dirty PTEs hw-dirty in
 pte_modify

On 04/12/2023 17:26, James Houghton wrote:
> Make it impossible to create a sw-dirty, hw-clean PTE with pte_modify.
> Such a PTE should be impossible to create, and there may be places that
> assume that pte_dirty() implies pte_hw_dirty().
> 
> Signed-off-by: James Houghton <jthoughton@...gle.com>

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index b19a8aee684c..79ce70fbb751 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -834,6 +834,12 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  		pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
>  
>  	pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
> +	/*
> +	 * If we end up clearing hw dirtiness for a sw-dirty PTE, set hardware
> +	 * dirtiness again.
> +	 */
> +	if (pte_sw_dirty(pte))
> +		pte = pte_mkdirty(pte);
>  	return pte;
>  }
>