On Mon, May 24, 2021 at 05:55:18PM +0200, Paolo Bonzini wrote:
> On 10/05/21 19:26, Marcelo Tosatti wrote:
> > +void vmx_pi_start_assignment(struct kvm *kvm)
> > +{
> > + struct kvm_vcpu *vcpu;
> > + int i;
> > +
> > + if (!irq_remapping_cap(IRQ_POSTING_CAP))
> > + return;
> > +
> > + /*
> > + * Wakeup will cause the vCPU to bail out of kvm_vcpu_block() and
> > + * go back through vcpu_block().
> > + */
> > + kvm_for_each_vcpu(i, vcpu, kvm) {
> > + if (!kvm_vcpu_apicv_active(vcpu))
> > + continue;
> > +
> > + kvm_vcpu_wake_up(vcpu);
>
> Would you still need the check_block callback, if you also added a
> kvm_make_request(KVM_REQ_EVENT)?
>
> In fact, since this is entirely not a hot path, can you just do
> kvm_make_all_cpus_request(kvm, KVM_REQ_EVENT) instead of this loop?
>
> Thanks,
>
> Paolo
Hi Paolo,
Don't think so:
int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
{
return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
}
static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
{
int ret = -EINTR;
int idx = srcu_read_lock(&vcpu->kvm->srcu);
if (kvm_arch_vcpu_runnable(vcpu)) {
kvm_make_request(KVM_REQ_UNHALT, vcpu); <---- don't want KVM_REQ_UNHALT
goto out;
}
if (kvm_cpu_has_pending_timer(vcpu))
goto out;
if (signal_pending(current))
goto out;
ret = 0;
out:
srcu_read_unlock(&vcpu->kvm->srcu, idx);
return ret;
}
See previous discussion:
Date: Wed, 12 May 2021 14:41:56 +0000
From: Sean Christopherson <seanjc@xxxxxxxxxx>
To: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Alex Williamson
<alex.williamson@xxxxxxxxxx>, Pei Zhang <pezhang@xxxxxxxxxx>
Subject: Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device
On Tue, May 11, 2021, Marcelo Tosatti wrote:
> > The KVM_REQ_UNBLOCK patch will resume execution even any such event
>
> even without any such event
>
> > occuring. So the behaviour would be different from baremetal.
I agree with Marcelo, we don't want to spuriously unhalt the vCPU. It's legal,
albeit risky, to do something like
hlt
/* #UD to triple fault if this CPU is awakened. */
ud2
when offlining a CPU, in which case the spurious wake event will crash the guest.
