[Devel] [PATCH hci-8.1 1/2] ms/vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc

From: Konstantin Khorenko <khorenko@virtuozzo.com>
To: Vasileios Almpanis <vasileios.almpanis@virtuozzo.com>,
	Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>,
	Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: devel@openvz.org
Subject: [Devel] [PATCH hci-8.1 1/2] ms/vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc
Date: Wed, 14 Oct 2026 19:16:26 +0200	[thread overview]
Message-ID: <20261014-b4-prep-khorenko-vstor-149847-6-vfio-exec-ms-backports-v1-1-07b4e541d4ec@virtuozzo.com> (raw)
In-Reply-To: <20261014-b4-prep-khorenko-vstor-149847-6-vfio-exec-ms-backports-v1-0-07b4e541d4ec@virtuozzo.com>

From: Junrui Luo <moonafterrain@outlook.com>

vfio_mig_get_next_state() walks vfio_from_fsm_table[] one step at a time,
looping to skip optional states the device does not support until
*next_fsm is supported. A blocked transition is encoded as
VFIO_DEVICE_STATE_ERROR, which the trailing return reports as -EINVAL.

The skip loop does not account for the ERROR sentinel.
state_flags_table[ERROR] is ~0U and vfio_from_fsm_table[ERROR][*] is
ERROR, so once *next_fsm becomes ERROR the loop condition stays true and
*next_fsm never changes. The blocked arcs STOP_COPY -> PRE_COPY and
STOP_COPY -> PRE_COPY_P2P map to ERROR yet pass the support check on a
precopy-capable device, causing the loop to spin forever while holding
the driver state mutex. This can result in a soft lockup, and a panic
with softlockup_panic set.

Terminate the skip loop on the ERROR sentinel so a blocked transition
falls through to the existing return and reports -EINVAL.

Fixes: 4db52602a607 ("vfio: Extend the device migration protocol with PRE_COPY")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/SYBPR01MB7881290BBDE79B61AE6A017FAF122@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
(cherry picked from commit a26b499b757cfc8bbff1088bb1b844639e250893)

https://virtuozzo.atlassian.net/browse/VSTOR-150235
Feature: fix ms/vfio

Assisted-by: LLM
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 drivers/vfio/vfio_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index f7df90c423b48..bf01fc64ee646 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -848,7 +848,8 @@ int vfio_mig_get_next_state(struct vfio_device *device,
 	 * logical state, as per the above comment.
 	 */
 	*next_fsm = vfio_from_fsm_table[cur_fsm][new_fsm];
-	while ((state_flags_table[*next_fsm] & device->migration_flags) !=
+	while (*next_fsm != VFIO_DEVICE_STATE_ERROR &&
+	       (state_flags_table[*next_fsm] & device->migration_flags) !=
 			state_flags_table[*next_fsm])
 		*next_fsm = vfio_from_fsm_table[*next_fsm][new_fsm];
 

-- 
2.43.0

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