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 <[email protected]>
> ---
> 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).
Perhaps moving atomic_set(&vcpu->guest_mode, 1) up to preemptible
section is safe, because kvm_vcpu_kick can only IPI stale vcpu->cpu
while preemption is enabled. In that case, it will hit
if (!atomic_read(&vcpu->guest_mode)
later.
Although the KVM_REQ_EVENT idea is nice. Can you think of a way
to fix the issue?
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