Re: [PATCH v3 44/59] KVM: arm/arm64: GICv4: Handle MOVI applied to a VLPI

Christoffer Dall
2017-08-30T20:02:48Z

On Wed, Aug 30, 2017 at 03:08:01PM +0100, Marc Zyngier wrote:
> On 28/08/17 19:18, Christoffer Dall wrote:
> > On Mon, Jul 31, 2017 at 06:26:22PM +0100, Marc Zyngier wrote:
> >> When the guest issues a MOVI, we need to tell the physical ITS
> >> that we're now targetting a new vcpu. This is done by extracting
> >> the current mapping, updating the target, and reapplying the
> >> mapping. The core ITS code should do the right thing.
> >>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> >> ---
> >> virt/kvm/arm/vgic/vgic-its.c | 13 +++++++++++++
> >> 1 file changed, 13 insertions(+)
> >>
> >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> >> index 79bac93d3e7d..aaad577ce328 100644
> >> --- a/virt/kvm/arm/vgic/vgic-its.c
> >> +++ b/virt/kvm/arm/vgic/vgic-its.c
> >> @@ -706,6 +706,19 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
> >> ite->irq->target_vcpu = vcpu;
> >> spin_unlock(&ite->irq->irq_lock);
> >>
> >> + if (ite->irq->hw) {
> >> + struct its_vlpi_map map;
> >> + int ret;
> >> +
> >> + ret = its_get_vlpi(ite->irq->host_irq, &map);
> >> + if (ret)
> >> + return ret;
> >> +
> >> + map.vpe_idx = vcpu->vcpu_id;
> >> +
> >> + return its_map_vlpi(ite->irq->host_irq, &map);
> >
> > Since you're not holding the irq_lock across these two calls, would it
> > be possible that the forwarding was removed through some other call path
> > here, and could you end up passing an invalid host_irq to its_map_vlpi?
> I believe we should be OK here, as we hold the ITS mutex during any
> command processing, and both the forward/unforward paths take that same
> mutex.

ok, yes, as long as the only other modifirs are the forward/unforward
paths and they hold the mutex, we should be fine.

>
> On a slightly different note, it looks like the MOVI code could benefit
> from using vgic_its_resolve_lpi(), which has been introduce earlier in
> this series.

Only problem is you'd need to get a handle to the ite as well to change
the collection pointer. I suppose you could add another pointer
pointer.

-Christoffer