linux-kernel - Re: [PATCH v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE

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Message-ID: <871rfylmdb.fsf@nanos.tec.linutronix.de>
Date:   Wed, 09 Dec 2020 22:07:12 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Cc:     peterz@...radead.org, luto@...nel.org,
        Juergen Gross <jgross@...e.com>,
        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 v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE

On Fri, Nov 20 2020 at 12:46, Juergen Gross 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.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Acked-by: Andy Lutomirski <luto@...nel.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>