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

[Gleb Natapov <gleb@redhat.com>]

On Tue, May 05, 2009 at 11:25:13AM +0200, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > 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.
> 
> Hmm, guess I have to re-read some manuals. But regarding
> rflags-after-iret, I think it should be cleared due to that restoring
> from the stack.
> 
Just re-tested this once more. DB is intercepted after IRET and TF/RF is
cleared already.

--
			Gleb.