linux-kernel - Re: [RFC PATCH 25/35] KVM: x86: Update __get_sregs() / __set

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Message-ID: <X8VKbLzEDc+W+jU/@google.com>
Date:   Mon, 30 Nov 2020 19:39:24 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC PATCH 25/35] KVM: x86: Update __get_sregs() / __set_sregs()
 to support SEV-ES

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?