Re: [PATCH 2/2] KVM: x86 emulator: Drop EFER.SVME requirement from VMMCALL

[Avi Kivity <avi@redhat.com>]

On 04/05/2011 04:41 PM, Joerg Roedel wrote:
> On Tue, Apr 05, 2011 at 04:28:31PM +0300, Avi Kivity wrote:
> >  VMMCALL requires EFER.SVME to be enabled in the host, not in the guest, which
> >  is what check_svme() checks.
>
> Well, yes and no. The guest has no dedicated EFER. EFER is switched in
> VMRUN which is why SVME must be set in the VMCBs EFER. This value makes
> it into the arch.efer too with Nested-SVM.
> According to the documentation VMMCALL throws an #UD if SVME is 0 which
> is why I added the check. On the other hand, at host-level it throws
> always an #UD and in the guest EFER.SVME is always enabled, so the check
> doesn't really make sense. I just added it because is is documented.

If the guest invokes VMMCALL, EFER.SVME refers to the host (and since 
we're running a guest, it's bound to be on).  However if a nested guest 
invokes VMMCALL, then EFER.SVME refers to the guest.  So the check 
should look something like

   if nested guest and not efer.svme:
        #UD

-- 
error compiling committee.c: too many arguments to function