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

Marcelo Tosatti
2011-02-17T16:53:28Z

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?