[Xen-devel] [PATCH] xen/events: fix unmask_evtchn for PV on HVM guests

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

When unmask_evtchn is called, if we already have an event pending, we
just set evtchn_pending_sel waiting for local_irq_enable to be called.
That is because PV guests set the irq_enable pvops to
xen_irq_enable_direct that also handles pending events.

However HVM guests (and ARM guests) do not change or do not have the
irq_enable pvop, so evtchn_unmask cannot work properly for them.

Considering that having the pending_irq bit set when unmask_evtchn is
called is not very common, and it is simpler to keep the
native_irq_enable implementation for HVM guests (and ARM guests), the
best thing to do is just use the EVTCHNOP_unmask hypercall (Xen
re-injects pending events in response).

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 drivers/xen/events.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index eae0d0b..0132505 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -372,8 +372,11 @@ static void unmask_evtchn(int port)
 
        BUG_ON(!irqs_disabled());
 
-       /* Slow path (hypercall) if this is a non-local port. */
-       if (unlikely(cpu != cpu_from_evtchn(port))) {
+       /* Slow path (hypercall) if this is a non-local port or if this is
+        * an hvm domain and an event is pending (hvm domains don't have
+        * their own implementation of irq_enable). */
+       if (unlikely((cpu != cpu_from_evtchn(port)) ||
+                       (xen_hvm_domain() && sync_test_bit(port, 
&s->evtchn_pending[0])))) {
                struct evtchn_unmask unmask = { .port = port };
                (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
        } else {

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