Re: [PATCH v5 3/7] KVM: X86: Expose IA32_PKRS MSR

[Chenyi Qiang]

On 11/9/2021 11:30 PM, Sean Christopherson wrote:
> On Tue, Nov 09, 2021, Chenyi Qiang wrote:
> > On 11/9/2021 1:44 AM, Sean Christopherson wrote:
> > > Hrm.  Ideally this would be open coded in vmx_set_msr().  Long term, the RESET/INIT
> > > paths should really treat MSR updates as "normal" host_initiated writes instead of
> > > having to manually handle every MSR.
> > >
> > > That would be a bit gross to handle in vmx_vcpu_reset() since it would have to
> > > create a struct msr_data (because __kvm_set_msr() isn't exposed to vendor code),
> > > but since vcpu->arch.pkrs is relevant to the MMU I think it makes sense to
> > > initiate the write from common x86.
> > >
> > > E.g. this way there's not out-of-band special code, vmx_vcpu_reset() is kept clean,
> > > and if/when SVM gains support for PKRS this particular path Just Works.  And it would
> > > be an easy conversion for my pipe dream plan of handling MSRs at RESET/INIT via a
> > > list of MSRs+values.
> > >
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index ac83d873d65b..55881d13620f 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -11147,6 +11147,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> > >           kvm_set_rflags(vcpu, X86_EFLAGS_FIXED);
> > >           kvm_rip_write(vcpu, 0xfff0);
> > >
> > > +       if (kvm_cpu_cap_has(X86_FEATURE_PKS))
> > > +               __kvm_set_msr(vcpu, MSR_IA32_PKRS, 0, true);
> > > +
> >
> > Got it. In addition, is it necessary to add on-INIT check? like:
> >
> > if (kvm_cpu_cap_has(X86_FEATURE_PKS) && !init_event)
> > 	__kvm_set_msr(vcpu, MSR_IA32_PKRS, 0, true);
> >
> > PKRS should be preserved on INIT, not cleared. The SDM doesn't make this
> > clear either.
>
> Hmm, but your cover letter says:
>
>    To help patches review, one missing info in SDM is that PKSR will be
>    cleared on Powerup/INIT/RESET, which should be listed in Table 9.1
>    "IA-32 and Intel 64 Processor States Following Power-up, Reset, or INIT"
>
> Which honestly makes me a little happy because I thought I was making stuff up
> for a minute :-)
>
> So which is it?

Sorry about the confusion. PKRS is preserved on INIT. I tried to correct 
my statement in previous ping mail but seems not so obvious.

>