Re: [PATCH 9/9] [SVM] inject NMI after IRET from a previous NMI, not before.

From: Gleb Natapov <gleb@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: avi@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH 9/9] [SVM] inject NMI after IRET from a previous NMI, not before.
Date: Tue, 5 May 2009 12:03:14 +0300	[thread overview]
Message-ID: <20090505090314.GN9795@redhat.com> (raw)
In-Reply-To: <49FFFCA0.3070507@siemens.com>

On Tue, May 05, 2009 at 10:45:20AM +0200, Jan Kiszka wrote:
> > @@ -2331,8 +2358,16 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
> >  {
> >  	struct vcpu_svm *svm = to_svm(vcpu);
> >  
> > -	if (svm->vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK)
> > -		enable_irq_window(vcpu);
> > +	if ((svm->vcpu.arch.hflags & (HF_NMI_MASK | HF_IRET_MASK))
> > +	    == HF_NMI_MASK)
> > +		return; /* IRET will cause a vm exit */
> > +
> > +	/* Something prevents NMI from been injected. Single step over
> > +	   possible problem (IRET or exception injection or interrupt
> > +	   shadow) */
> > +	vcpu->arch.singlestep = true;
> > +	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
> 
> Can you single-step like this out of an IRQ handler? I mean, IRET will
> restore the flags from the stack, and those settings should be
> overwritten. Or am I missing something?
> 
It seems to be working :) Shouldn't CPU checks single step before
executing IRET and thus using old flags value? It is interesting to
check what rflag value is immediately after IRET.

--
			Gleb.