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

Avi Kivity
2011-02-16T09:01:50Z

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.

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error compiling committee.c: too many arguments to function