Re: [PATCH v4 5/6] KVM: nVMX: Fix conditions for NMI injection

[Gleb Natapov <gleb@redhat.com>]

On Sun, Apr 14, 2013 at 05:53:05PM +0200, Jan Kiszka wrote:
> On 2013-04-14 17:23, Gleb Natapov wrote:
> > On Sun, Apr 14, 2013 at 12:12:49PM +0200, Jan Kiszka wrote:
> >> From: Jan Kiszka <jan.kiszka@siemens.com>
> >>
> >> The logic for checking if interrupts can be injected has to be applied
> >> also on NMIs. The difference is that if NMI interception is on these
> >> events are consumed and blocked by the VM exit.
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >> ---
> >>  arch/x86/kvm/vmx.c |   28 ++++++++++++++++++++++++++++
> >>  1 files changed, 28 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> >> index 56e7519..ad9b4bc 100644
> >> --- a/arch/x86/kvm/vmx.c
> >> +++ b/arch/x86/kvm/vmx.c
> >> @@ -4190,6 +4190,12 @@ static bool nested_exit_on_intr(struct kvm_vcpu *vcpu)
> >>  		PIN_BASED_EXT_INTR_MASK;
> >>  }
> >>  
> >> +static bool nested_exit_on_nmi(struct kvm_vcpu *vcpu)
> >> +{
> >> +	return get_vmcs12(vcpu)->pin_based_vm_exec_control &
> >> +		PIN_BASED_NMI_EXITING;
> >> +}
> >> +
> >>  static void enable_irq_window(struct kvm_vcpu *vcpu)
> >>  {
> >>  	u32 cpu_based_vm_exec_control;
> >> @@ -4315,6 +4321,28 @@ static void vmx_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
> >>  
> >>  static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
> >>  {
> >> +	if (is_guest_mode(vcpu)) {
> >> +		struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> >> +
> >> +		if (to_vmx(vcpu)->nested.nested_run_pending ||
> >> +		    vmcs_read32(GUEST_ACTIVITY_STATE) ==
> >> +			   GUEST_ACTIVITY_WAIT_SIPI)
> > The same is true for interrupt too,
> 
> Yes, but aren't we already waiting with interrupts disabled in that state?
> 
Why? L1 can do vmcs_write(GUEST_ACTIVITY_STATE,
GUEST_ACTIVITY_WAIT_SIPI) at any point.

> > but I do not think that we should allow
> > nested guest directly enter GUEST_ACTIVITY_WAIT_SIPI state or any other
> > state except ACTIVE. They should be emulated instead.
> 
> Well, they aren't emulated yet but directly applied. So I think the
> patch is correct in the current context at least.
> 
If my understanding is correct the facts that it is directly applied is
a serious bug and should be fixed.

> What negative effects do you expect from entering those states with L2?
> 
As I wrote below (and you misunderstood me :)) it looks like L0 external
interrupts do not generate vmexit while active VMCS is in Wait-For-SIPI
state. In any case we should carefully examine what are the implications
of this state since KVM never uses it and does not know how to handle it.

> > From quick look at
> > the spec it looks like external interrupts do not cause VMEXIT while
> > vcpu is in GUEST_ACTIVITY_WAIT_SIPI.
> 
> Yes, see above.
> 
> Jan
> 
> 



--
			Gleb.