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

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Message-ID: <3f5bd68d-7b2f-8b1f-49b9-0e59587513c8@redhat.com>
Date:   Mon, 30 Nov 2020 19:28:01 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     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 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?

Paolo