linux-kernel - Re: [PATCH v4 1/1] x86/cpufeatures: Implement Predictive Store Forwarding control.

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Date:   Fri, 30 Apr 2021 18:50:26 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     "Saripalli, RK" <rsaripal@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, Borislav Petkov <bp@...en8.de>, hpa@...or.com,
        Jonathan Corbet <corbet@....net>, bsd@...hat.com
Subject: Re: [PATCH v4 1/1] x86/cpufeatures: Implement Predictive Store
 Forwarding control.

> > Considering KVM/virtualization for a CPU that has X86_FEATURE_PSFD
> > but no other existing feature with MSR_IA32_SPEC_CTRL, if a host
> > doesn't enable PSFD with the new parameter, the host doesn't have
> > X86_FEATURE_MSR_SPEC_CTRL.  Then, it would be a problem if its
> > guests want to use PSFD looking at x86_virt_spec_ctrl().
> > (I'm not sure how you will change your previous KVM patch though)
>
> Reiji, you are correct that X86_FEATURE_MSR_SPEC_CTRL should be enabled so KVM guests can use PSFD
> even if host does not use it.
> I have this change in my KVM patch.


Thank you for the response. Yes, that sounds good.

Thanks,
Reiji