Subject: [patch 28/30] xen/events: Reduce irq_info::spurious_cnt storage size

From: Thomas Gleixner <[email-masked]>
Date: Thu, 10 Dec 2020 20:26:04 +0100

To prepare for interrupt spreading reduce the storage size of
irq_info::spurious_cnt to u8 so the required flag for the spreading logic
will not increase the storage size.

Protect the usage site against overruns.

Signed-off-by: Thomas Gleixner <[email-masked]>
Cc: Boris Ostrovsky <[email-masked]>
Cc: Juergen Gross <[email-masked]>
Cc: Stefano Stabellini <[email-masked]>
Cc: [email-masked]
---
 drivers/xen/events/events_base.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -95,7 +95,7 @@ struct irq_info {
 	struct list_head list;
 	struct list_head eoi_list;
 	short refcnt;
-	short spurious_cnt;
+	u8 spurious_cnt;
 	enum xen_irq_type type; /* type */
 	unsigned irq;
 	evtchn_port_t evtchn;   /* event channel */
@@ -528,8 +528,10 @@ static void xen_irq_lateeoi_locked(struc
 		return;
 
 	if (spurious) {
-		if ((1 << info->spurious_cnt) < (HZ << 2))
-			info->spurious_cnt++;
+		if ((1 << info->spurious_cnt) < (HZ << 2)) {
+			if (info->spurious_cnt != 0xFF)
+				info->spurious_cnt++;
+		}
 		if (info->spurious_cnt > 1) {
 			delay = 1 << (info->spurious_cnt - 2);
 			if (delay > HZ)