Re: NMI Injection to Guest

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jul 27, 2009 at 01:11:46AM +0530, Nipun sehrawat wrote:
> Hi all,
> 
> What about using vmx_inject_nmi(vcpu) to inject the NMIs into the
> guest, when we are sure about the vcpu on which the NMI is to be
> injected.
> 
The only save place to call it is were it is called now. If you want
vmx_inject_nmi(vcpu) to be called set vcpu->arch.nmi_pending to 1.

> Nipun
> 
> On Mon, Jul 27, 2009 at 12:55 AM, Jiaqing Du <jiaqing@gmail.com> wrote:
> >
> > Hi Gleb,
> >
> > Thanks for your reply.
> >
> > 2009/7/26 Gleb Natapov <gleb@redhat.com>:
> > > On Sat, Jul 25, 2009 at 10:46:39PM +0200, Jiaqing Du wrote:
> > >> Hi list,
> > >>
> > >> I'm trying to extend OProfile to support guest profiling. One step of
> > >> my work is to push an NMI to the guest(s) when a performance counter
> > >> overflows. Please correct me if the following is not correct:
> > >>
> > >> counter overflow --> NMI to host --> VM exit --> "int $2" to handle
> > >> NMI on host --> ...   --> VM entry --> NMI to guest
> > >>
> > > Correct except the last step (--> NMI to guest). Host nmi is not
> > > propagated to guests.
> >
> > Yes. I need to add some code to propagate host NMI to guests.
> > >
> > >> On the path between VM-exit and VM-entry, I want to push an NMI to the
> > >> guest. I tried to put the following code on the path, but never
> > >> succeeded. Various wired things happened, such as KVM hangs, guest
> > >> kernel oops, and host hangs. I tried both code with Linux 2.6.30 and
> > >> version 88.
> > >>
> > >> if (vmx_nmi_allowed())  { vmx_inject_nmi(); }
> > >>
> > >> Any suggestions? Where is the right place to push an NMI and what are
> > >> the necessary checks?
> > > Call kvm_inject_nmi(vcpu). And don't forget to vcpu_load(vcpu) before
> > > doing it. See kvm_vcpu_ioctl_nmi().
> >
> > Based on the code with Linux 2.6.30, what kvm_inject_nmi(vcpu) does is
> > just set vcpu->arch.nmi_pending to 1. kvm_vcpu_ioctl_nmi() puts
> > vcpu_load() before the setting and vcpu_put() after it.
> >
> > I need to push host NMI to guests between a VM-exit and a VM-entry
> > after that. The VM-exit is due to an NMI caused by performance counter
> > overflow. The following code with vcpu_enter_guest(), which is
> > surrounded by a vcpu_load() and vcpu_put(), checks this
> > vcpu->arch.nmi_pending and other related flags to decide whether an
> > NMI should be pushed to guests.
> >
> >        if (vcpu->arch.exception.pending)
> >                __queue_exception(vcpu);
> >        else if (irqchip_in_kernel(vcpu->kvm))
> >                kvm_x86_ops->inject_pending_irq(vcpu);
> >        else
> >                kvm_x86_ops->inject_pending_vectors(vcpu, kvm_run);
> >
> > What I did is given below:
> >
> > 3097 static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> > 3098 {
> >               ... ...
> >
> > 3156         if (kvm_vm_exit_on_cnt_overflow) {
> > 3157                 vcpu->arch.nmi_pending = 1;
> > 3158         }
> > 3159
> > 3160         if (vcpu->arch.exception.pending)
> > 3161                 __queue_exception(vcpu);
> > 3162         else if (irqchip_in_kernel(vcpu->kvm))
> > 3163                 kvm_x86_ops->inject_pending_irq(vcpu);
> > 3164         else
> > 3165                 kvm_x86_ops->inject_pending_vectors(vcpu, kvm_run);
> >
> >              ... ....
> > 3236 }
> >
> > In vcpu_enter_guest(), before this part of code is reached,
> > vcpu->arch.nmi_pending is set to 1 if the VM-exit is due to
> > performance counter overflow. Still, no NMIs are seen by the guests. I
> > also tried to put this "vcpu->arch.nmi_pending = 1;" somewhere else on
> > the path between a VM-exit and VM-entry, it does not seem to work
> > neither. Only vmx_inject_nmi() manages to push NMIs to guests, but
> > without right sanity checks, it causes various wired host and guest
> > behaviors.
> >
> > To inject NMIs on the path between a VM-exit and VM-entry, what's to try next?
> >
> > >
> > > --
> > >                        Gleb.
> > >
> >
> > Thanks,
> > Jiaqing
> > --
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--
			Gleb.