Re: [PATCH 2/3] KVM: VMX: Short circuit STI; HLT while an interrupt is pending

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Feb 17, 2011 at 11:12:43AM +0200, Avi Kivity wrote:
> >>  >>   index ee1cd1a..541da0e 100644
> >>  >>   --- a/arch/x86/kvm/vmx.c
> >>  >>   +++ b/arch/x86/kvm/vmx.c
> >>  >>   @@ -3437,6 +3437,15 @@ static int handle_interrupt_window(struct kvm_vcpu *vcpu)
> >>  >>    static int handle_halt(struct kvm_vcpu *vcpu)
> >>  >>    {
> >>  >>    	skip_emulated_instruction(vcpu);
> >>  >>   +	/*
> >>  >>   +	 * Short-circuit an STI; HLT sequence while an interrupt is pending:
> >>  >>   +	 * instead of halting, re-entering the guest, and exiting immediately
> >>  >>   +	 * on an interrupt window exit, go directly to the last step.
> >>  >>   +	 */
> >>  >>   +	if ((to_vmx(vcpu)->cpu_based_vm_exec_control
> >>  >>   +	&   CPU_BASED_VIRTUAL_INTR_PENDING)
> >>  >>   +	&&   (kvm_get_rflags(vcpu)&   X86_EFLAGS_IF))
> >>  >>   +		return handle_interrupt_window(vcpu);
> >>  >>    	return kvm_emulate_halt(vcpu);
> >>  >>    }
> >>  >
> >>  >Why does the normal vcpu entry path fails to inject the interrupt? Because after halt,
> >>  >KVM_REQ_EVENT is not set?
> >>
> >>  Yes.  Also, we want to clear CPU_BASED_VIRTUAL_INTR_PENDING.
> >
> >Is there a reason why it cannot be handled in the main loop?
> 
> Don't follow.  What are you suggesting?

That vcpu main loop (inject_pending_events etc) should be able to inject
the interrupt and clear interrupt exiting, instead of a short circuit
in specific exit handlers, as an improvement on top of the current
patchset. Any numbers, BTW?