Re: [PATCH 4/4] kvm: svm: Support KVM_SEV_SNP_PAGE_TYPE_VMSA at SNP_LAUNCH_UPDATE

[Sean Christopherson <seanjc@google.com>]

On Wed, Jun 17, 2026, Jörg Rödel wrote:
> On Wed, Jun 17, 2026 at 06:37:52AM -0700, Sean Christopherson wrote:
> > Ok, so it took us a few times to learn our lesson.  I still don't see that as a
> > strong argument for new uAPI, especially not for VMSA pages.  I am very firmly
> > of the opinion that letting anything but the host kernel configure the VMSA is
> > beyond stupid, but unfortunately we're stuck with AP_CREATION.  Expanding that
> > surface has a very, very, VERY high bar to get over.
> 
> The strongest argument in my view (and the main reason we are doing this) is
> actually the predictable launch measurement. On SEV-SNP this is a requirement
> to use platform VM-identity features like the ID Block.

And I'm saying that unless KVM *can't* provide a predictable launch measurement,
which AIUI isn't the case, then the launch measurement *must* be stable across
kernels because it's part of KVM's ABI.  So as I see it, the issue isn't that
KVM is inherently unpredictable, it's that we lack tests to validate a thorny,
subtle piece of KVM's ABI.

In other words, I want tests, not more complexity in KVM.