linux-kernel - Re: [RESUBMIT][PATCH] x86/mm: Fix PAT bit missing from page protection modify mask

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Date:   Wed, 31 May 2023 20:14:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Yu Zhao <yuzhao@...gle.com>, linux-kernel@...r.kernel.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        drm-intel@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RESUBMIT][PATCH] x86/mm: Fix PAT bit missing from page
 protection modify mask

On Fri, May 19, 2023 at 08:36:34PM +0200, Janusz Krzysztofik wrote:
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 15ae4d6ba4768..56466afd04307 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -654,8 +654,10 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>  #define pgprot_modify pgprot_modify
>  static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
>  {
> -	pgprotval_t preservebits = pgprot_val(oldprot) & _PAGE_CHG_MASK;
> -	pgprotval_t addbits = pgprot_val(newprot) & ~_PAGE_CHG_MASK;
> +	unsigned long mask = _PAGE_CHG_MASK | _PAGE_CACHE_MASK;
> +
> +	pgprotval_t preservebits = pgprot_val(oldprot) & mask;
> +	pgprotval_t addbits = pgprot_val(newprot) & ~mask;
>  	return __pgprot(preservebits | addbits);
>  }
>  
> -- 

This certainly needs Jürgen and he's on CC already, moving him to To:.

Also, why isn't this a Xen-specific fix but you're keeping _PAGE_PAT for
baremetal too, i.e., modifying the generic function?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette