linux-kernel - Re: [PATCH] x86/vsyscall/64: Use proper accessor to update p4d entry

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Message-ID: <CALCETrXNm4H2kq76yM1Cc2+LEqimrrG2eY8BagNpii-JEaSP9Q@mail.gmail.com>
Date:   Tue, 20 Mar 2018 03:42:54 +0000
From:   Andy Lutomirski <luto@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] x86/vsyscall/64: Use proper accessor to update p4d entry

On Mon, Mar 19, 2018 at 2:31 PM, Boris Ostrovsky
<boris.ostrovsky@...cle.com> wrote:
> Writing to it directly does not work for Xen PV guests.

Whoops, my bad.

Acked-by: Andy Lutomirski <luto@...nel.org>

>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index 8560ef68a9d6..317be365bce3 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -347,7 +347,7 @@ void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
>         set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
>         p4d = p4d_offset(pgd, VSYSCALL_ADDR);
>  #if CONFIG_PGTABLE_LEVELS >= 5
> -       p4d->p4d |= _PAGE_USER;
> +       set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
>  #endif
>         pud = pud_offset(p4d, VSYSCALL_ADDR);
>         set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
> --
> 2.14.3
>