Re: [PATCH] kvm: svm: Only propagate next_rip when guest supports it

[Joerg Roedel <joro@8bytes.org>]

On Wed, Oct 07, 2015 at 11:48:36AM -0400, Bandan Das wrote:
> Ok, understood now. The warn_on would trigger in L1 only if it has
> decided to disable nrips for some reason as was the case here. So,
> my reasoning behind putting the warning was incorrect.

Okay, so I think the warning can be removed.

> > +
> > +	if (guest_cpuid_has_nrips(vcpu))
> > +		nested_vmcb->control.next_rip  = vmcb->control.next_rip;

Note that there is a bug here, instead of vcpu it must be &svm->vcpu.
Somehow I missed to at least compile-test this.

Dirk is currently testing whether this (fixed) patch solves the problem
in his setup.

> >  
> >  	/*
> >  	 * If we emulate a VMRUN/#VMEXIT in the same host #vmexit cycle we have
> > @@ -2714,6 +2716,9 @@ static bool nested_svm_vmrun(struct vcpu_svm *svm)
> >  	svm->vmcb->control.event_inj = nested_vmcb->control.event_inj;
> >  	svm->vmcb->control.event_inj_err = nested_vmcb->control.event_inj_err;
> >  
> > +	/* Clear next_rip, as real hardware would do */
> > +	nested_vmcb->control.next_rip = 0;
> > +
> 
> Why do we need this ? And are you sure this is what real hardware does ?
> I couldn't find anything in the spec.

Yeah, probably right. Since we only write guests next_rip when the guest
supports it via cpuid, there is probably no point in resetting it at
vmrun emulation.


	Joerg