linux-kernel - Re: [PATCH 3/4] x86/pv: switch SWAPGS to ALTERNATIVE

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Message-ID: <CALCETrWwnK1AwrGRn8Kuin-23NOG31LrWBO7w=T2QE+EJW=f-w@mail.gmail.com>
Date:   Mon, 16 Nov 2020 08:17:29 -0800
From:   Andy Lutomirski <luto@...nel.org>
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>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Deep Shah <sdeep@...are.com>,
        "VMware, Inc." <pv-drivers@...are.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH 3/4] x86/pv: switch SWAPGS to ALTERNATIVE

On Mon, Nov 16, 2020 at 7:23 AM Juergen Gross <jgross@...e.com> wrote:
>
> SWAPGS is used only for interrupts coming from user mode or for
> returning to user mode. So there is no reason to use the PARAVIRT
> framework, as it can easily be replaced by an ALTERNATIVE depending
> on X86_FEATURE_XENPV.
>
> There are several instances using the PV-aware SWAPGS macro in paths
> which are never executed in a Xen PV guest. Replace those with the
> plain swapgs instruction. For SWAPGS_UNSAFE_STACK the same applies.

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