Re: [tip: x86/seves] x86/kvm: Add KVM-specific VMMCALL handling under SEV-ES

[Joerg Roedel <jroedel@xxxxxxx>]

On Wed, Oct 28, 2020 at 11:03:05AM -0700, Erdem Aktas wrote:
> I might be missing something here but I think what you say is only
> correct for the kvm_hypercall4 cases. All other functions use a
> smaller number of registers. #VC blindly assumes that all those
> registers are used in the vmcall and exposes them.

Right, I think we should fix that in the guest and zero out the unused
registers. VMMCALL can come from userspace after all, and the #VC
handler does not look at the hypercall numbers.

Further, on the host side KVM will unconditionally read out all 4
registers too, which requires us to set them valid in the GHCB.

Regards,

	Joerg