xen: use PHYSDEVOP_get_free_pirq to implement find_unbound_pirq

Use the new hypercall PHYSDEVOP_get_free_pirq to ask Xen to allocate a
pirq. Remove the unsupported PHYSDEVOP_get_nr_pirqs hypercall to get the
amount of pirq available.

This fixes find_unbound_pirq that otherwise would return a number
starting from nr_irqs that might very well be out of range in Xen.

The symptom of this bug is that when you passthrough an MSI capable pci
device to a PV on HVM guest, Linux would fail to enable MSIs on the
device.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

2 files changed, 30 insertions, 25 deletions

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 2811bb988ea0..7ab43c33f746 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -105,7 +105,6 @@ struct irq_info
 
 static struct irq_info *irq_info;
 static int *pirq_to_irq;
-static int nr_pirqs;
 
 static int *evtchn_to_irq;
 struct cpu_evtchn_s {
@@ -385,12 +384,17 @@ static int get_nr_hw_irqs(void)
         return ret;
 }
 
-/* callers of this function should make sure that PHYSDEVOP_get_nr_pirqs
- * succeeded otherwise nr_pirqs won't hold the right value */
-static int find_unbound_pirq(void)
+static int find_unbound_pirq(int type)
 {
-        int i;
-        for (i = nr_pirqs-1; i >= 0; i--) {
+        int rc, i;
+        struct physdev_get_free_pirq op_get_free_pirq;
+        op_get_free_pirq.type = type;
+
+        rc = HYPERVISOR_physdev_op(PHYSDEVOP_get_free_pirq, &op_get_free_pirq);
+        if (!rc)
+                return op_get_free_pirq.pirq;
+
+        for (i = 0; i < nr_irqs; i++) {
                 if (pirq_to_irq[i] < 0)
                         return i;
         }
@@ -611,10 +615,10 @@ int xen_map_pirq_gsi(unsigned pirq, unsigned gsi, int shareable, char *name)
 
         spin_lock(&irq_mapping_update_lock);
 
-        if ((pirq > nr_pirqs) || (gsi > nr_irqs)) {
+        if ((pirq > nr_irqs) || (gsi > nr_irqs)) {
                 printk(KERN_WARNING "xen_map_pirq_gsi: %s %s is incorrect!\n",
-                        pirq > nr_pirqs ? "nr_pirqs" :"",
-                        gsi > nr_irqs ? "nr_irqs" : "");
+                        pirq > nr_irqs ? "pirq" :"",
+                        gsi > nr_irqs ? "gsi" : "");
                 goto out;
         }
 
@@ -672,7 +676,7 @@ void xen_allocate_pirq_msi(char *name, int *irq, int *pirq)
         if (*irq == -1)
                 goto out;
 
-        *pirq = find_unbound_pirq();
+        *pirq = find_unbound_pirq(MAP_PIRQ_TYPE_MSI);
         if (*pirq == -1)
                 goto out;
 
@@ -1506,26 +1510,17 @@ void xen_callback_vector(void) {}
 
 void __init xen_init_IRQ(void)
 {
-        int i, rc;
-        struct physdev_nr_pirqs op_nr_pirqs;
+        int i;
 
         cpu_evtchn_mask_p = kcalloc(nr_cpu_ids, sizeof(struct cpu_evtchn_s),
                                     GFP_KERNEL);
         irq_info = kcalloc(nr_irqs, sizeof(*irq_info), GFP_KERNEL);
 
-        rc = HYPERVISOR_physdev_op(PHYSDEVOP_get_nr_pirqs, &op_nr_pirqs);
-        if (rc < 0) {
-                nr_pirqs = nr_irqs;
-                if (rc != -ENOSYS)
-                        printk(KERN_WARNING "PHYSDEVOP_get_nr_pirqs returned rc=%d\n", rc);
-        } else {
-                if (xen_pv_domain() && !xen_initial_domain())
-                        nr_pirqs = max((int)op_nr_pirqs.nr_pirqs, nr_irqs);
-                else
-                        nr_pirqs = op_nr_pirqs.nr_pirqs;
-        }
-        pirq_to_irq = kcalloc(nr_pirqs, sizeof(*pirq_to_irq), GFP_KERNEL);
-        for (i = 0; i < nr_pirqs; i++)
+        /* We are using nr_irqs as the maximum number of pirq available but
+         * that number is actually chosen by Xen and we don't know exactly
+         * what it is. Be careful choosing high pirq numbers. */
+        pirq_to_irq = kcalloc(nr_irqs, sizeof(*pirq_to_irq), GFP_KERNEL);
+        for (i = 0; i < nr_irqs; i++)
                 pirq_to_irq[i] = -1;
 
         evtchn_to_irq = kcalloc(NR_EVENT_CHANNELS, sizeof(*evtchn_to_irq),
diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
index 2b2c66c3df00..534cac89a77d 100644
--- a/include/xen/interface/physdev.h
+++ b/include/xen/interface/physdev.h
@@ -188,6 +188,16 @@ struct physdev_nr_pirqs {
     uint32_t nr_pirqs;
 };
 
+/* type is MAP_PIRQ_TYPE_GSI or MAP_PIRQ_TYPE_MSI
+ * the hypercall returns a free pirq */
+#define PHYSDEVOP_get_free_pirq    23
+struct physdev_get_free_pirq {
+    /* IN */ 
+    int type;
+    /* OUT */
+    uint32_t pirq;
+};
+
 /*
  * Notify that some PIRQ-bound event channels have been unmasked.
  * ** This command is obsolete since interface version 0x00030202 and is **