From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH 13/15] Add NMI injection support to SVM.
Date: Sun, 19 Apr 2009 16:17:35 +0300
Message-ID: <20090419131735.GG10126@redhat.com>
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	sheng@linux.intel.com, Dmitry Baryshkov <dbaryshkov@gmail.com>
To: Jan Kiszka <jan.kiszka@web.de>
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On Fri, Apr 17, 2009 at 09:55:45PM +0200, Jan Kiszka wrote:
> Gleb Natapov wrote:
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |    1 +
> >  arch/x86/kvm/svm.c              |   49 +++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 48 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 8b6f6e9..057a612 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -766,6 +766,7 @@ enum {
> >  #define HF_GIF_MASK		(1 << 0)
> >  #define HF_HIF_MASK		(1 << 1)
> >  #define HF_VINTR_MASK		(1 << 2)
> > +#define HF_NMI_MASK		(1 << 3)
> >  
> >  /*
> >   * Hardware virtualization extension instructions may fault if a
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index c605477..cd60fd7 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -1834,6 +1834,13 @@ static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> >  	return 1;
> >  }
> >  
> > +static int iret_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> > +{
> > +	svm->vmcb->control.intercept &= ~(1UL << INTERCEPT_IRET);
> > +	svm->vcpu.arch.hflags &= ~HF_NMI_MASK;
> > +	return 0;
> > +}
> 
> First, this must return 1 (or set an exit reason, but there is no reason
> to escape to user space here). And second, I think a corner case is not
> handled the same way as on real iron: If there is already the next NMI
> waiting, we will inject it before iret, not after its execution as it
> should be.
> 
> No easy solution for this yet. Maybe emulating iret, but there is no
> implementation, specifically for protected mode. Maybe setting a
> breakpoint. Or maybe enforcing a single step exception. Nothing trivial
> in this list. On the other hand, this may only be a slight imprecision
> of the virtualization. Need to think about it.
> 
What about this:
Instead of clearing HF_NMI_MASK in iret_interception() we can set
another flag (HF_IRET) and on guest entry clear HF_NMI_MASK (and
HF_IRET) if HF_IRET is set, but do that after checking for NMI
injection. The pending NMI will be injected on the next entry.
Also not how real HW works, but may be better then current situation.


--
			Gleb.