From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Date: Thu, 7 May 2026 15:43:49 +0000 (+0000)
Subject: mshv: Fix duplicate GSI detection for GSI 0
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=649dd135491945afa544351e3e6d4a727de87020;p=thirdparty%2Flinux.git

mshv: Fix duplicate GSI detection for GSI 0

The duplicate routing entry check in mshv_update_routing_table() uses
guest_irq_num != 0 to detect whether a GSI slot is already occupied.
This fails for GSI 0 because its guest_irq_num is 0 both when the slot
is unused (zero-initialized) and when legitimately assigned. As a
result, duplicate entries for GSI 0 are silently accepted, with the
second entry overwriting the first — corrupting the routing table
without any error reported to userspace.

While GSI 0 (legacy timer) is unlikely to appear in MSI-based routing
in practice, the check is semantically wrong — it conflates
"uninitialized" with "GSI number 0." Use girq_entry_valid instead,
which is explicitly set to true when an entry is populated and remains
zero for unused slots regardless of the GSI number.

Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
---

diff --git a/drivers/hv/mshv_irq.c b/drivers/hv/mshv_irq.c
index b3142c84dcbc..65a4ffc82d56 100644
--- a/drivers/hv/mshv_irq.c
+++ b/drivers/hv/mshv_irq.c
@@ -51,7 +51,7 @@ int mshv_update_routing_table(struct mshv_partition *partition,
 		/*
 		 * Allow only one to one mapping between GSI and MSI routing.
 		 */
-		if (girq->guest_irq_num != 0) {
+		if (girq->girq_entry_valid) {
 			r = -EINVAL;
 			goto out;
 		}