linux-kernel - Re: [PATCH 0/3] KVM: x86: XSS and XCR0 fixes

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Date:   Thu, 27 Jan 2022 15:03:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>,
        Like Xu <likexu@...cent.com>
Subject: Re: [PATCH 0/3] KVM: x86: XSS and XCR0 fixes

On Thu, Jan 27, 2022, Paolo Bonzini wrote:
> On 1/26/22 18:48, Sean Christopherson wrote:
> > On Wed, Jan 26, 2022, Paolo Bonzini wrote:
> > > On 1/26/22 18:22, Sean Christopherson wrote:
> > > > For convenience, Like's patch split up and applied on top of Xiaoyao.
> > > > Tagged all for @stable, probably want to (retroactively?) get Xiaoyao's
> > > > patch tagged too?
> > > > Like Xu (2):
> > > >     KVM: x86: Update vCPU's runtime CPUID on write to MSR_IA32_XSS
> > > >     KVM: x86: Sync the states size with the XCR0/IA32_XSS at, any time
> > > > 
> > > > Xiaoyao Li (1):
> > > >     KVM: x86: Keep MSR_IA32_XSS unchanged for INIT
> > > > 
> > > >    arch/x86/kvm/x86.c | 6 +++---
> > > >    1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > 
> > > > base-commit: e2e83a73d7ce66f62c7830a85619542ef59c90e4
> > > 
> > > Queued, though I'll note that I kinda disagree with the stable@ marking of
> > > patch 1 (and therefore with the patch order) as it has no effect in
> > > practice.
> > 
> > Hmm, that's not a given, is it?  E.g. the guest can configure XSS early on and
> > then expect the configured value to live across INIT-SIPI-SIPI.  I agree it's
> > highly unlikely for any guest to actually do that, but I don't like assuming all
> > guests will behave a certain way.
> 
> No, I meant in the sense that supported_xss is always zero right now, and
> therefore so is MSR_IA32_XSS.

Oh, duh.