xen/intr: fix fallout from r278854

r278854 introduced a race in the event channel handling code. We must make
sure that the pending bit is cleared before executing the filter, or else we
might miss other events that would be injected after the filter has ran but
before the pending bit is cleared.

While there also mask event channels while FreeBSD executes the ithread
bound to that event channel. This refrains Xen from injecting more
interrupts while the ithread has not finished it's work.

Sponsored by: Citrix Systems R&D
Reported by: sbruno, robak
Tested by: robak

1 files changed, 23 insertions, 14 deletions

diff --git a/sys/x86/xen/xen_intr.c b/sys/x86/xen/xen_intr.c
index a964fac7161c..64979b136ead 100644
--- a/sys/x86/xen/xen_intr.c
+++ b/sys/x86/xen/xen_intr.c
@@ -128,6 +128,7 @@ struct xenisrc {
 	u_int		xi_close:1;	/* close on unbind? */
 	u_int		xi_activehi:1;
 	u_int		xi_edgetrigger:1;
+	u_int		xi_masked:1;
 };
 
 #define ARRAY_SIZE(a)	(sizeof(a) / sizeof(a[0]))
@@ -578,12 +579,11 @@ xen_intr_handle_upcall(struct trapframe *trap_frame)
 
 			/* process port */
 			port = (l1i * LONG_BIT) + l2i;
+			synch_clear_bit(port, &s->evtchn_pending[0]);
 
 			isrc = xen_intr_port_to_isrc[port];
-			if (__predict_false(isrc == NULL)) {
-				synch_clear_bit(port, &s->evtchn_pending[0]);
+			if (__predict_false(isrc == NULL))
 				continue;
-			}
 
 			/* Make sure we are firing on the right vCPU */
 			KASSERT((isrc->xi_cpu == PCPU_GET(cpuid)),
@@ -930,11 +930,21 @@ out:
  *              acknowledgements.
  */
 static void
-xen_intr_disable_source(struct intsrc *isrc, int eoi)
+xen_intr_disable_source(struct intsrc *base_isrc, int eoi)
 {
+	struct xenisrc *isrc;
 
-	if (eoi == PIC_EOI)
-		xen_intr_eoi_source(isrc);
+	isrc = (struct xenisrc *)base_isrc;
+
+	/*
+	 * NB: checking if the event channel is already masked is
+	 * needed because the event channel user-space device
+	 * masks event channels on it's filter as part of it's
+	 * normal operation, and those shouldn't be automatically
+	 * unmasked by the generic interrupt code. The event channel
+	 * device will unmask them when needed.
+	 */
+	isrc->xi_masked = !!evtchn_test_and_set_mask(isrc->xi_port);
 }
 
 /*
@@ -943,8 +953,14 @@ xen_intr_disable_source(struct intsrc *isrc, int eoi)
  * \param isrc  The interrupt source to unmask (if necessary).
  */
 static void
-xen_intr_enable_source(struct intsrc *isrc)
+xen_intr_enable_source(struct intsrc *base_isrc)
 {
+	struct xenisrc *isrc;
+
+	isrc = (struct xenisrc *)base_isrc;
+
+	if (isrc->xi_masked == 0)
+		evtchn_unmask_port(isrc->xi_port);
 }
 
 /*
@@ -955,11 +971,6 @@ xen_intr_enable_source(struct intsrc *isrc)
 static void
 xen_intr_eoi_source(struct intsrc *base_isrc)
 {
-	struct xenisrc *isrc;
-
-	isrc = (struct xenisrc *)base_isrc;
-	synch_clear_bit(isrc->xi_port,
-	    &HYPERVISOR_shared_info->evtchn_pending[0]);
 }
 
 /*
@@ -1025,8 +1036,6 @@ xen_intr_pirq_eoi_source(struct intsrc *base_isrc)
 
 	isrc = (struct xenisrc *)base_isrc;
 
-	synch_clear_bit(isrc->xi_port,
-	    &HYPERVISOR_shared_info->evtchn_pending[0]);
 	if (test_bit(isrc->xi_pirq, xen_intr_pirq_eoi_map)) {
 		struct physdev_eoi eoi = { .irq = isrc->xi_pirq };