[PATCH 2/2] xen/irq: Don't fall over when nr_irqs_gsi > nr_irqs.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

This scenario where the nr_irq_gsi is greater than nr_irqs
is rather strange but lets still try to survive. Make sure
to print a warning so the user wouldn't be surprised in case
things don't work.

Solves a bootup-crash when booting Xen and Linux under QEMU.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/xen/events.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 4d4a23d..11687dd 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -411,6 +411,7 @@ static int find_unbound_irq(void)
 	if (bottom == nr_irqs)
 		goto no_irqs;
 
+retry:
 	/* 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)
@@ -434,6 +435,14 @@ static int find_unbound_irq(void)
 		goto no_irqs;
 
 	res = irq_alloc_desc_at(irq, -1);
+	if (res == -EEXIST) {
+		top--;
+		if (bottom > top)
+			printk(KERN_ERR "Eating in GSI/MSI space (%ld)!" \
+				" Your PCI device might not work!\n", top);
+		if (top > NR_IRQS_LEGACY)
+			goto retry;
+	}
 
 	if (WARN_ON(res != irq))
 		return -1;
-- 
1.7.1