linux-kernel - Re: [PATCH v3 10/15] KVM: x86: add fields to struct kvm

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Date: Thu, 14 Mar 2024 15:56:27 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Michael Roth <michael.roth@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	aik@....com, pankaj.gupta@....com
Subject: Re: [PATCH v3 10/15] KVM: x86: add fields to struct kvm_arch for CoCo features

On Thu, Mar 14, 2024, Michael Roth wrote:
> On Wed, Mar 13, 2024 at 09:49:52PM -0500, Michael Roth wrote:
> > I've been trying to get SNP running on top of these patches and hit and
> > issue with these due to fpstate_set_confidential() being done during
> > svm_vcpu_create(), so when QEMU tries to sync FPU state prior to calling
> > SNP_LAUNCH_FINISH it errors out. I think the same would happen with
> > SEV-ES as well.
> > 
> > Maybe fpstate_set_confidential() should be relocated to SEV_LAUNCH_FINISH
> > site as part of these patches?
> 
> Talked to Tom a bit about this and that might not make much sense unless
> we actually want to add some code to sync that FPU state into the VMSA
> prior to encryption/measurement. Otherwise, it might as well be set to
> confidential as soon as vCPU is created.
> 
> And if userspace wants to write FPU register state that will not actually
> become part of the guest state, it probably does make sense to return an
> error for new VM types and leave it to userspace to deal with
> special-casing that vs. the other ioctls like SET_REGS/SREGS/etc.

Won't regs and sregs suffer the same fate?  That might not matter _today_ for
"real" VMs, but it would be a blocking issue for selftests, which need to stuff
state to jumpstart vCPUs.

And maybe someday real VMs will catch up to the times and stop starting at the
RESET vector...