1 files changed, 27 insertions, 50 deletions

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 81a53eb6cd1d..06f2e61de691 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -376,72 +376,49 @@ static void unmask_evtchn(int port)
         put_cpu();
 }
 
-static int get_nr_hw_irqs(void)
+static int xen_allocate_irq_dynamic(void)
 {
-        int ret = 1;
+        int first = 0;
+        int irq;
 
 #ifdef CONFIG_X86_IO_APIC
-        ret = get_nr_irqs_gsi();
+        /*
+         * For an HVM guest or domain 0 which see "real" (emulated or
+         * actual repectively) GSIs we allocate dynamic IRQs
+         * e.g. those corresponding to event channels or MSIs
+         * etc. from the range above those "real" GSIs to avoid
+         * collisions.
+         */
+        if (xen_initial_domain() || xen_hvm_domain())
+                first = get_nr_irqs_gsi();
 #endif
 
-        return ret;
-}
+retry:
+        irq = irq_alloc_desc_from(first, -1);
 
-static int xen_allocate_irq_dynamic(void)
-{
-        struct irq_data *data;
-        int irq, res;
-        int bottom = get_nr_hw_irqs();
-        int top = nr_irqs-1;
-
-        if (bottom == nr_irqs)
-                goto no_irqs;
-
-        /* This loop starts from the top of IRQ space and goes down.
-         * We need this b/c if we have a PCI device in a Xen PV guest
-         * we do not have an IO-APIC (though the backend might have them)
-         * mapped in. To not have a collision of physical IRQs with the Xen
-         * event channels start at the top of the IRQ space for virtual IRQs.
-         */
-        for (irq = top; irq > bottom; irq--) {
-                data = irq_get_irq_data(irq);
-                /* only 15->0 have init'd desc; handle irq > 16 */
-                if (!data)
-                        break;
-                if (data->chip == &no_irq_chip)
-                        break;
-                if (data->chip != &xen_dynamic_chip)
-                        continue;
-                if (irq_info[irq].type == IRQT_UNBOUND)
-                        return irq;
+        if (irq == -ENOMEM && first > NR_IRQS_LEGACY) {
+                printk(KERN_ERR "Out of dynamic IRQ space and eating into GSI space. You should increase nr_irqs\n");
+                first = max(NR_IRQS_LEGACY, first - NR_IRQS_LEGACY);
+                goto retry;
         }
 
-        if (irq == bottom)
-                goto no_irqs;
-
-        res = irq_alloc_desc_at(irq, -1);
-
-        if (WARN_ON(res != irq))
-                return -1;
+        if (irq < 0)
+                panic("No available IRQ to bind to: increase nr_irqs!\n");
 
         return irq;
-
-no_irqs:
-        panic("No available IRQ to bind to: increase nr_irqs!\n");
-}
-
-static bool identity_mapped_irq(unsigned irq)
-{
-        /* identity map all the hardware irqs */
-        return irq < get_nr_hw_irqs();
 }
 
 static int xen_allocate_irq_gsi(unsigned gsi)
 {
         int irq;
 
-        if (!identity_mapped_irq(gsi) &&
-            (xen_initial_domain() || !xen_pv_domain()))
+        /*
+         * A PV guest has no concept of a GSI (since it has no ACPI
+         * nor access to/knowledge of the physical APICs). Therefore
+         * all IRQs are dynamically allocated from the entire IRQ
+         * space.
+         */
+        if (xen_pv_domain() && !xen_initial_domain())
                 return xen_allocate_irq_dynamic();
 
         /* Legacy IRQ descriptors are already allocated by the arch. */