linux-kernel - Re: [PATCH 2/4] x86/xen: use specific Xen pv interrupt entry for DF

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Message-ID: <CALCETrWVSEB5zrUiZ81KaB5egx78TfDuSDv+qR3HFtJ=SKxwkQ@mail.gmail.com>
Date:   Mon, 16 Nov 2020 08:12:46 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Juergen Gross <jgross@...e.com>
Cc:     xen-devel <xen-devel@...ts.xenproject.org>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH 2/4] x86/xen: use specific Xen pv interrupt entry for DF

On Mon, Nov 16, 2020 at 7:23 AM Juergen Gross <jgross@...e.com> wrote:
>
> Xen PV guests don't use IST. For double fault interrupts switch to
> the same model as NMI.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/include/asm/idtentry.h | 3 +++
>  arch/x86/xen/enlighten_pv.c     | 8 +++++++-
>  arch/x86/xen/xen-asm.S          | 2 +-
>  3 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index 3505c0396fa5..b35825392547 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -611,6 +611,9 @@ DECLARE_IDTENTRY_RAW(X86_TRAP_DB,   xenpv_exc_debug);
>
>  /* #DF */
>  DECLARE_IDTENTRY_DF(X86_TRAP_DF,       exc_double_fault);
> +#ifdef CONFIG_XEN_PV
> +DECLARE_IDTENTRY_RAW_ERRORCODE(X86_TRAP_DF,    xenpv_exc_double_fault);
> +#endif
>
>  /* #VC */
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 9f5e44c1f70a..803fbcb398c4 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -571,6 +571,12 @@ DEFINE_IDTENTRY_RAW(xenpv_exc_nmi)
>         exc_nmi(regs);
>  }
>
> +DEFINE_IDTENTRY_RAW_ERRORCODE(xenpv_exc_double_fault)
> +{
> +       /* On Xen PV, DF doesn't use IST.  The C part is the sane as native. */

I would like to think that code is sane, but you probably meant "same".

> +       exc_double_fault(regs, error_code);
> +}