On (21/07/12 17:24), Marc Zyngier wrote:
> >
> > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> > {
> > + kvm_update_vcpu_preempted(vcpu, true);
>
> This doesn't look right. With this, you are now telling the guest that
> a vcpu that is blocked on WFI is preempted. This really isn't the
> case, as it has voluntarily entered a low-power mode while waiting for
> an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't
> be running either.
I suppose you are talking about kvm_vcpu_block(). Well, it checks
kvm_vcpu_check_block() but then it simply schedule() out the vcpu
process, which does look like "the vcpu is preempted". Once we
sched_in() that vcpu process again we mark it as non-preempted,
even though it remains in kvm wfx handler. Why isn't it right?
Another call path is iret:
<iret>
__schedule()
context_switch()
prepare_task_switch()
fire_sched_in_preempt_notifiers()
kvm_sched_out()
kvm_arch_vcpu_put()
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