linux-kernel - Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism to write MSR

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Message-ID: <E1BAF52C-A955-466A-B5A2-DE12876FBFCF@zytor.com>
Date: Fri, 25 Apr 2025 08:29:10 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Peter Zijlstra <peterz@...radead.org>,
        Jürgen Groß <jgross@...e.com>
CC: Xin Li <xin@...or.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
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Subject: Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism to write MSR

On April 25, 2025 5:33:17 AM PDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Wed, Apr 23, 2025 at 06:05:19PM +0200, Jürgen Groß wrote:
>
>> > It's not a major change, but when it is patched to use the immediate
>> > form MSR write instruction, it's straightforwardly streamlined.
>> 
>> It should be rather easy to switch the current wrmsr/rdmsr paravirt patching
>> locations to use the rdmsr/wrmsr instructions instead of doing a call to
>> native_*msr().
>
>Right, just make the Xen functions asm stubs that expect the instruction
>registers instead of C-abi and ALT_NOT_XEN the thing.
>
>Shouldn't be hard at all.

And that's what we will be doing. We already have code for that.