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

H. Peter Anvin
2025-04-25T20:14:03Z

On April 25, 2025 5:51:27 AM PDT, "Jürgen Groß" <jgross@suse.com> wrote:
>On 25.04.25 14:33, Peter Zijlstra 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.
>
>Correct. And for the new immediate form we can use ALTERNATIVE_3().
>
>
>Juergen

Yes; in the ultimate case there are *four* alternatives, but the concept is the same and again we have it implemented already.