Re: [PATCH v2 5/5] KVM: nVMX: Enable nested posted interrupt processing.

[Paolo Bonzini <pbonzini@redhat.com>]

On 20/01/2015 09:48, Wincy Van wrote:
> +static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu,
> +                                               int vector)
> +{
> +       int r = 0;
> +       struct vmcs12 *vmcs12;
> +
> +       /*
> +        * Since posted intr delivery is async,
> +        * we must aquire a spin-lock to avoid
> +        * the race of vmcs12.
> +        */
> +       spin_lock(&to_vmx(vcpu)->nested.vmcs12_lock);
> +       vmcs12 = get_vmcs12(vcpu);
> +       if (!is_guest_mode(vcpu) || !vmcs12) {
> +               r = -1;
> +               goto out;
> +       }

is_guest_mode should be checked first outside the lock, to avoid
affecting the non-nested fast path.  You can then recheck it later
inside the lock.

Another way to avoid the spinlock: in prepare_vmcs02 or a similar place,
you can save vmcs12->posted_intr_nv in a new field
vmx->nested.posted_intr_nv; just set it to -1 if
!nested_cpu_has_posted_intr(vmcs12).  In vmclear, again you just set the
field to -1, and here you can do

	if (!is_guest_mode(vcpu) ||
	    vector != to_vmx(vcpu)->nested.posted_intr_nv) {
		r = -1;
		goto out;
	}

You don't need to access vmcs12, and while there is a race, it's okay
because there is no pointer access.

> 
> +               if (vcpu->mode == IN_GUEST_MODE)
> +                       apic->send_IPI_mask(get_cpu_mask(vcpu->cpu),
> +                               POSTED_INTR_VECTOR);

Please add a comment that PIR and ON have been set by the L1 hypervisor.

I'll do a full review the other patches as soon as possible.

Paolo

> +               else {
> +                       r = -1;
> +                       goto out;
> +               }
> +
> +               /*
> +                * if posted intr is done by hardware, the
> +                * corresponding eoi was sent to L0. Thus
> +                * we should send eoi to L1 manually.
> +                */
> +               kvm_apic_set_eoi_accelerated(vcpu,
> +                       vmcs12->posted_intr_nv);