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

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Date:   Mon, 11 Dec 2023 11:01:38 -0800
From:   James Houghton <jthoughton@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     Steve Capper <steve.capper@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ryan Roberts <ryan.roberts@....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 Mon, Dec 11, 2023 at 10:42 AM Will Deacon <will@...nel.org> wrote:
>
> On Mon, Dec 04, 2023 at 05:26:46PM +0000, 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>
>
> I'm not sure how, but you seem to be missing the '---' separator and the
> diffstat here, so I suspect this might confuse tools such as b4 which try
> to apply the patch directly.

Thanks for pointing that out. Looks like it came from using
`--summary` in git format-patch. :/

>
> > 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;
>
> Looks like this is a fix for Catalin to pick up (patch #1 isn't necessary
> afaict).

If only this patch is taken, make sure to add cc:stable and the fixes
tag from patch #1. Thank you!