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

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Date:   Thu, 27 Jan 2022 13:09:35 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.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 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.

Paolo