Re: [PATCH 2/4] selftests/kvm: check that SEV-ES VMs are allowed in SEV-SNP mode

[Sean Christopherson <seanjc@google.com>]

On Mon, Feb 23, 2026, Tycho Andersen wrote:
> > > +	/*
> > > +	 * In some cases when SEV-SNP is enabled, firmware disallows starting
> > > +	 * an SEV-ES VM. When SEV-SNP is enabled try to launch an SEV-ES, and
> > > +	 * check the underlying firmware error for this case.
> > > +	 */
> > > +	vm = vm_sev_create_with_one_vcpu(KVM_X86_SEV_ES_VM, guest_sev_es_code,
> > > +					 &vcpu);
> > 
> > If there's a legimate reason why an SEV-ES VM can't be created, then that needs
> > to be explicitly enumerated in some way by the kernel.  E.g. is this due to lack
> > of ASIDs due to CipherTextHiding or something?
> 
> Newer firmware that fixes CVE-2025-48514 won't allow SEV-ES VMs to be
> started with SNP enabled, there is a footnote (2) about it here:
> 
> https://www.amd.com/en/resources/product-security/bulletin/amd-sb-3023.html
> 
> Probably should have included this in the patch, sorry.
> 
> > Throwing a noodle to see if it sticks is not an option.
> 
> Sure, we could do some firmware version test to see if it's fixed
> instead? Or do this same test in the kernel and export that as an
> ioctl?

Uh, no idea what would be ideal, but there absolutely needs to be some way to
communicate lack of effective SEV-ES support to userspace, and in a way that
doesn't break userspace.

Hrm, I think we also neglected to communicate when SEV and SEV-ES are effectively
unusable, e.g. due to CipherTextHiding, so maybe we can kill two birds with one
stone?  IIRC, we didn't bother enumerating the limitation with CipherTextHiding
because making SEV-ES unusable would require a deliberate act from the admin.

"Update firmware" is also an deliberate act, but the side effect of SEV-ES being
disabled, not so much.