Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form when available

[Borislav Petkov]

On Mon, Mar 31, 2025 at 04:27:23PM -0400, Konrad Rzeszutek Wilk wrote:
> Is that the right path forward?
> 
> That is replace the MSR write to disable speculative execution with a
> non-serialized WRMSR? Doesn't that mean the WRMSRNS is speculative?

Ha, interesting question.

If the WRMSR is non-serializing, when do speculative things like indirect
branches and the like get *actually* cleared and can such a speculation window
be used to leak branch data even if IBRS is actually enabled for example...

Fun.

This change needs to be run by hw folks and I guess until then WRMSRNS should
not get anywhere near mitigation MSRs like SPEC_CTRL or PRED_CMD...

Thx.

-- 
Regards/Gruss,
    Boris.

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