From: Juergen Gross <jgross@suse.com>
Date: Thu, 5 May 2022 06:35:31 +0000 (+0200)
Subject: xen/grant-table: never put a reserved grant on the free list
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=eb3042a4b2a6d47aae1c556c0bad958bcc868e5f;p=people%2Fjgross%2Flinux.git

xen/grant-table: never put a reserved grant on the free list

Make sure a reserved grant is never put on the free list, as this could
cause hard to debug errors.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
V3:
- new patch
---

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 6ea31ea26008..1a1aec0a88a1 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -207,6 +207,10 @@ static inline void check_free_callbacks(void)
 static void put_free_entry(grant_ref_t ref)
 {
 	unsigned long flags;
+
+	if (unlikely(ref < GNTTAB_NR_RESERVED_ENTRIES))
+		return;
+
 	spin_lock_irqsave(&gnttab_list_lock, flags);
 	gnttab_entry(ref) = gnttab_free_head;
 	gnttab_free_head = ref;