Re: [PATCH 1/6] KVM: Check for pending events before attempting injection

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Jul 28, 2010 at 07:53:32PM +0300, Avi Kivity wrote:
>  On 07/28/2010 07:37 PM, Marcelo Tosatti wrote:
> >On Wed, Jul 28, 2010 at 07:31:03PM +0300, Avi Kivity wrote:
> >>  On 07/28/2010 07:21 PM, Marcelo Tosatti wrote:
> >>>On Tue, Jul 27, 2010 at 04:19:35PM +0300, Avi Kivity wrote:
> >>>>Instead of blindly attempting to inject an event before each guest entry,
> >>>>check for a possible event first in vcpu->requests.  Sites that can trigger
> >>>>event injection are modified to set KVM_REQ_EVENT:
> >>>>
> >>>>- interrupt, nmi window opening
> >>>>- ppr updates
> >>>>- i8259 output changes
> >>>>- local apic irr changes
> >>>>- rflags updates
> >>>>- gif flag set
> >>>>- event set on exit
> >>>>
> >>>>This improves non-injecting entry performance, and sets the stage for
> >>>>non-atomic injection.
> >>>>
> >>>>Signed-off-by: Avi Kivity<avi@redhat.com>
> >>>>---
> >>>>  arch/x86/kvm/i8259.c     |    1 +
> >>>>  arch/x86/kvm/lapic.c     |   12 ++++++++++--
> >>>>  arch/x86/kvm/svm.c       |    8 +++++++-
> >>>>  arch/x86/kvm/vmx.c       |    6 ++++++
> >>>>  arch/x86/kvm/x86.c       |   35 ++++++++++++++++++++++++++---------
> >>>>  include/linux/kvm_host.h |    1 +
> >>>>  6 files changed, 51 insertions(+), 12 deletions(-)
> >>>>
> >>>>@@ -4731,17 +4737,19 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >>>>  		goto out;
> >>>>  	}
> >>>>
> >>>>-	inject_pending_event(vcpu);
> >>>>+	if (kvm_check_request(KVM_REQ_EVENT, vcpu)) {
> >>>>+		inject_pending_event(vcpu);
> >>>>
> >>>>-	/* enable NMI/IRQ window open exits if needed */
> >>>>-	if (vcpu->arch.nmi_pending)
> >>>>-		kvm_x86_ops->enable_nmi_window(vcpu);
> >>>>-	else if (kvm_cpu_has_interrupt(vcpu) || req_int_win)
> >>>>-		kvm_x86_ops->enable_irq_window(vcpu);
> >>>>+		/* enable NMI/IRQ window open exits if needed */
> >>>>+		if (vcpu->arch.nmi_pending)
> >>>>+			kvm_x86_ops->enable_nmi_window(vcpu);
> >>>>+		else if (kvm_cpu_has_interrupt(vcpu) || req_int_win)
> >>>>+			kvm_x86_ops->enable_irq_window(vcpu);
> >>>Problem is it might not be possible to inject the event signalled by
> >>>KVM_REQ_EVENT, say an interrupt from an irqchip, if there is an event
> >>>that needs reinjection (or an exception).
> >>That can happen event now, no?  A pending exception, interrupt comes
> >>along, injection picks up the exception but leaves the interrupt.
> >>
> >>Now the situation can be more complicated:
> >>
> >>- pending exception
> >>- injection
> >>- interrupt, sets KVM_REQ_EVENT
> >>- notices KVM_REQ_EVENT
> >>- drops KVM_REQ_EVENT, cancels exception (made pending again)
> >>- goes back
> >>- injection (injects exception again, interrupt is pending)
> >>
> >>as far as I can tell, this is all fine.
> >But you cleared KVM_REQ_EVENT. Which means you're not going to inject
> >the pending interrupt on the next entry.
> 
> Doh.  So we need to set KVM_REQ_EVENT again, after the final check
> for vcpu->requests, to make sure we redo injection again.
> 
> So we can make inject_pending_event() return true if there's more in
> the queue, and if it did, re-raise KVM_REQ_EVENT just before entry?

Yeah, that would do it.