Re: [PATCH v4 09/15] KVM: SEV: sync FPU and AVX state at LAUNCH_UPDATE_VMSA time

[Paolo Bonzini]

On Mon, Mar 25, 2024 at 12:43 AM Michael Roth <michael.roth@xxxxxxx> wrote:
> There may have be userspaces that previously relied on KVM_SET_XSAVE
> being silently ignored when calculating the expected VMSA measurement.
> Granted, that's sort of buggy behavior on the part of userspace, but QEMU
> for instance does this. In that case, it just so happens that QEMU's reset
> values don't appear to affect the VMSA measurement/contents, but there may
> be userspaces where it would.
>
> To avoid this, and have parity with the other interfaces where the new
> behavior is gated on the new vm_type/KVM_SEV_INIT2 stuff (via
> has_protected_state), maybe should limited XSAVE/FPU sync'ing to
> has_protected_state as well?

Yes, in particular I am kinda surprised that MXCSR (whose default
value after reset is 0x1F80) does not affect the measurement.

Paolo