To make x86 irq allocation to be same with booting path and ioapic
hot add path, We will pre-reserve irq for all gsi at first.
We have to use alloc_reserved here, otherwise irq_alloc_desc_at will fail
because bit is already get marked for pre-reserved in irq bitmaps.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xensource.com
---
 drivers/xen/events.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index a58ac43..1a3647c 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -507,8 +507,12 @@ static int __must_check xen_allocate_irq_gsi(unsigned gsi)
 	/* Legacy IRQ descriptors are already allocated by the arch. */
 	if (gsi < NR_IRQS_LEGACY)
 		irq = gsi;
-	else
-		irq = irq_alloc_desc_at(gsi, -1);
+	else {
+		/* for x86, irq already get reserved for gsi */
+		irq = irq_alloc_reserved_desc_at(gsi, -1);
+		if (irq < 0)
+			irq = irq_alloc_desc_at(gsi, -1);
+	}
 
 	xen_irq_init(irq);
 
-- 
1.8.1.4