Re: [PATCH v3 09/16] x86/msr: Use the alternatives mechanism for WRMSR

[Dave Hansen]

On 2/18/26 13:00, Sean Christopherson wrote:
> On Wed, Feb 18, 2026, Juergen Gross wrote:
>> When available use one of the non-serializing WRMSR variants (WRMSRNS
>> with or without an immediate operand specifying the MSR register) in
>> __wrmsrq().
> Silently using a non-serializing version (or not) seems dangerous (not for KVM,
> but for the kernel at-large), unless the rule is going to be that MSR writes need
> to be treated as non-serializing by default.

Yeah, there's no way we can do this in general. It'll work for 99% of
the MSRs on 99% of the systems for a long time. Then the one new system
with WRMSRNS is going to have one hell of a heisenbug that'll take years
off some poor schmuck's life.

We should really encourage *new* code to use wrmsrns() when it can at
least for annotation that it doesn't need serialization. But I don't
think we should do anything to old, working code.