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

[no-reply at sashiko.virtuozzo.com]

> From: Junrui Luo <moonafterrain at 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.
> [ ... ]
> https://virtuozzo.atlassian.net/browse/VSTOR-150235
> Feature: fix ms/vfio
> 
> Assisted-by: LLM
> Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261014-b4-prep-khorenko-vstor-149847-6-vfio-exec-ms-backports-v1-0-07b4e541d4ec@virtuozzo.com?part=1