Re: [PATCH 06/13] KVM: SVM: Add VNMI bit definition

Sean Christopherson
2022-11-17T20:33:55Z

On Thu, Nov 17, 2022, Borislav Petkov wrote:
> On Thu, Nov 17, 2022 at 04:42:57PM +0000, Sean Christopherson wrote:
> > Why? This is rarely run code, won't cpu_feature_enabled()
> > unnecessarily require patching?
>
> Because we want one single interface to test X86_FEATURE flags. And
> there's no need for the users to know whether it wants patching or not -
> we simply patch *everywhere* and that's it.
>
> > And while we're on the topic... https://lore.kernel.org/all/Y22IzA9DN%2FxYWgWN@google.com
>
> Because static_ or boot_ is not relevant to the user - all she
> wants to know is whether a cpu feature has been enabled. Thus
> cpu_feature_enabled().
>
> And yes, at the time I protested a little about unnecessary patching.
> And tglx said "Why not?". And I had no good answer to that. So we can
> just as well patch *everywhere*.

Ah, I missed that memo.

Paolo,

Since it sounds like static_cpu_has() is going the way of the dodo, and ditto for
boot_cpu_has() except for flows that don't play nice with patching (none of which
are in KVM), should we do a KVM-wide conversion to cpu_feature_enabled() at some
point in the near future?