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

[Avi Kivity <avi@redhat.com>]

On 02/15/2011 10:36 PM, Marcelo Tosatti wrote:
> On Mon, Feb 14, 2011 at 04:42:16PM +0200, Avi Kivity wrote:
> >  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.
> >
> >  Saves a vmexit on workloads where interrupts are received synchronously;
> >  an example is a disk backed by the host page cache where there is no
> >  latency (from the guest's point of view) between the request and fulfilment.
> >
> >  Signed-off-by: Avi Kivity<avi@redhat.com>
> >  ---
> >   arch/x86/kvm/vmx.c |    9 +++++++++
> >   1 files changed, 9 insertions(+), 0 deletions(-)
> >
> >  diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> >  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.

-- 
error compiling committee.c: too many arguments to function