Re: [PATCH v2 1/5] KVM: nSVM: deal with L1 hypervisor that intercepts interrupts but lets L2 control EFLAGS.IF

[Maxim Levitsky <mlevitsk@redhat.com>]

On Mon, 2021-12-13 at 14:15 +0100, Paolo Bonzini wrote:
> On 12/13/21 14:07, Maxim Levitsky wrote:
> > > Right, another case is when CLGI is not trapped and the guest therefore
> > > runs with GIF=0.  I think that means that a similar change has to be
> > > done in all the *_allowed functions.
> > 
> > I think that SVM sets real GIF to 1 on VMentry regardless if it is trapped or not.
> 
> Yes, the issue is only when CLGI is not trapped (and vGIF is disabled).

Yes, but I just wanted to clarify that GIF is initially enabled on VM entry
regardless if it is trapped or not, after that the guest can indeed disable
the GIF if CLGI/STGI is not trapped and vGIF disabled.

> 
> > However if not trapped, and neither EFLAGS.IF is trapped, one could enter a guest
> > that has EFLAGS.IF == 0, then the guest could disable GIF, enable EFLAGS.IF,
> > and then enable GIF, but then GIF enablement should trigger out interrupt window
> > VINTR as well.
> 
> While GIF=0 you have svm_nmi_blocked returning true and svm_nmi_allowed 
> returning -EBUSY; that's wrong isn't it?

Yes, 100% agree, patch (and unit test for this as well) is on the way!

Best regards.	
	Maxim Levitsky
> 
> Paolo
>