xen: do not map the same GSI twice in PVHVM guests.

PV on HVM guests map GSIs into event channels. At restore time the
event channels are resumed by restore_pirqs.

Device drivers might try to register the same GSI again through ACPI at
restore time, but the GSI has already been mapped and bound by
restore_pirqs. This patch detects these situations and avoids
 mapping the same GSI multiple times.

Without this patch we get:
(XEN) irq.c:2235: dom4: pirq 23 or emuirq 28 already mapped
and waste a pirq.

CC: stable@kernel.org
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/pci/xen.c

@@ -64,6 +64,10 @@ static int xen_register_pirq(u32 gsi, int gsi_override, int triggering,
 	int shareable = 0;
 	char *name;
 
+	irq = xen_irq_from_gsi(gsi);
+	if (irq > 0)
+		return irq;
+
 	if (set_pirq)
 		pirq = gsi;
 

drivers/xen/events.c

@@ -611,7 +611,7 @@ static void disable_pirq(struct irq_data *data)
 	disable_dynirq(data);
 }
 
-static int find_irq_by_gsi(unsigned gsi)
+int xen_irq_from_gsi(unsigned gsi)
 {
 	struct irq_info *info;
 
@@ -625,6 +625,7 @@ static int find_irq_by_gsi(unsigned gsi)
 
 	return -1;
 }
+EXPORT_SYMBOL_GPL(xen_irq_from_gsi);
 
 /*
  * Do not make any assumptions regarding the relationship between the
@@ -644,7 +645,7 @@ int xen_bind_pirq_gsi_to_irq(unsigned gsi,
 
 	mutex_lock(&irq_mapping_update_lock);
 
-	irq = find_irq_by_gsi(gsi);
+	irq = xen_irq_from_gsi(gsi);
 	if (irq != -1) {
 		printk(KERN_INFO "xen_map_pirq_gsi: returning irq %d for gsi %u\n",
 		       irq, gsi);

include/xen/events.h

@@ -103,6 +103,9 @@ int xen_irq_from_pirq(unsigned pirq);
 /* Return the pirq allocated to the irq. */
 int xen_pirq_from_irq(unsigned irq);
 
+/* Return the irq allocated to the gsi */
+int xen_irq_from_gsi(unsigned gsi);
+
 /* Determine whether to ignore this IRQ if it is passed to a guest. */
 int xen_test_irq_shared(int irq);