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Date:   Mon, 30 Nov 2020 19:39:24 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [RFC PATCH 25/35] KVM: x86: Update __get_sregs() / __set_sregs()
 to support SEV-ES
Message-ID: <X8VKbLzEDc+W+jU/@google.com>
References: <cover.1600114548.git.thomas.lendacky@amd.com>
 <e08f56496a52a3a974310fbe05bb19100fd6c1d8.1600114548.git.thomas.lendacky@amd.com>
 <20200914213708.GC7192@sjchrist-ice>
 <7fa6b074-6a62-3f8e-f047-c63851ebf7c9@amd.com>
 <20200915163342.GC8420@sjchrist-ice>
 <6486b1f3-35e2-bcb0-9860-1df56017c85f@amd.com>
 <20200915224410.GI8420@sjchrist-ice>
 <3f5bd68d-7b2f-8b1f-49b9-0e59587513c8@redhat.com>
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On Mon, Nov 30, 2020, Paolo Bonzini wrote:
> On 16/09/20 00:44, Sean Christopherson wrote:
> > > KVM doesn't have control of them. They are part of the guest's encrypted
> > > state and that is what the guest uses. KVM can't alter the value that the
> > > guest is using for them once the VMSA is encrypted. However, KVM makes
> > > some decisions based on the values it thinks it knows.  For example, early
> > > on I remember the async PF support failing because the CR0 that KVM
> > > thought the guest had didn't have the PE bit set, even though the guest
> > > was in protected mode. So KVM didn't include the error code in the
> > > exception it injected (is_protmode() was false) and things failed. Without
> > > syncing these values after live migration, things also fail (probably for
> > > the same reason). So the idea is to just keep KVM apprised of the values
> > > that the guest has.
> > 
> > Ah, gotcha.  Migrating tracked state through the VMSA would probably be ideal.
> > The semantics of __set_sregs() kinda setting state but not reaaaally setting
> > state would be weird.
> 
> How would that work with TDX?

Can you elaborate?  I.e. how would what work with TDX?