linux-kernel - Re: [PATCH] KVM: x86: Expose Predictive Store Forwarding Disable

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Message-ID: <bcd40d94-2634-a40c-0173-64063051a4b2@redhat.com>
Date:   Mon, 27 Sep 2021 14:14:52 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Babu Moger <babu.moger@....com>, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, hpa@...or.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tony.luck@...el.com, peterz@...radead.org,
        kyung.min.park@...el.com, wei.huang2@....com, jgross@...e.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Expose Predictive Store Forwarding Disable

On 27/09/21 14:06, Borislav Petkov wrote:
>> Because the guest kernel needs to know which MSRs to write when you touch
>> the SSBD prctl, so that PSFD is properly disabled*inside the guest*.
> It already knows which - the same one which disables SSB. PSF is
> disabled*together*  with SSB, for now...

Right, not which MSR to write but which value to write.  It doesn't know 
that the PSF disable bit is valid unless the corresponding CPUID bit is set.

Paolo