Re: [PATCH RFC V5 2/6] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

Sorry for late reply,
was on vacation for a week (without IMAP access :( )

On 04/12/2012 05:36 AM, Marcelo Tosatti wrote:
> On Fri, Mar 23, 2012 at 01:37:04PM +0530, Raghavendra K T wrote:
> > From: Srivatsa Vaddagiri<vatsa@xxxxxxxxxxxxxxxxxx>
[snip]
> > @@ -1567,6 +1568,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> >   		prepare_to_wait(&vcpu->wq,&wait, TASK_INTERRUPTIBLE);
> >
> >   		if (kvm_arch_vcpu_runnable(vcpu)) {
> > +			vcpu->pv_unhalted = 0;
> > +			/* preventing reordering should be enough here */
> > +			barrier();
>
> Is it always OK to erase the notification, even in case an unrelated
> event such as interrupt was the source of wakeup?


Erasing notification is not good, But I think in this case,

kvm_make_request(KVM_REQ_UNHALT, vcpu);

below this would take care of the rest.

> It would be easier to verify that notifications are not lost with atomic
>
> test_and_clear(pv_unhalted).

true, I 'll verify that (with pv_unhalt as atomic variable). my heart
says  current code is just fine, since we are about to unblock.

> Also x86 specific code should remain in arch/x86/kvm/

I agree. 'll have clear function in arch/x86/kvm and add stub to rest
of the archs

>

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