Re: [PATCH 0/2] virtio_pci_modern: fix vp_reset() hang on unresponsive device

[Michael S. Tsirkin]

On Sun, Aug 02, 2026 at 05:40:57PM +0000, Abhin Parekadan Jose wrote:
> While investigating a syzbot report of a WARN_ON_ONCE firing in
> virtio_dev_remove() [1],


And I responded to that syzbot report, and I quote:

So it writes 0 into pci command, effectively killing the device,
and then is unhappy that the driver prints warnings?
Who thought it's a good idea? Why?


> I found a related but more serious issue:
> vp_reset() in the modern virtio-pci transport can hang indefinitely
> if PCI_COMMAND memory-space decode is disabled while the device is
> bound (e.g. surprise removal, hardware fault, or -- as reproduced
> here -- a direct write to the PCI_COMMAND register). The status
> register poll loop has no way to distinguish "device still resetting"
> from "device unreachable," so it never terminates.
> 
> Patch 1 adds a VIRTIO_STATUS_ERROR() check that recognizes an
> all-ones status read as invalid (per spec, bits 4-5 are reserved and
> can never legitimately be set) and warns once at the point the bad
> read actually happens.
> 
> Patch 2 uses that check to break out of vp_reset()'s poll loop
> instead of spinning forever.

Was all this including the cover letter written with ai assistance?
if yes pls disclose this.

> Reproduced on a modern-transport virtio-blk-pci device:
> 
>   # printf '\x00\x00' | dd of=/sys/bus/pci/devices/0000:01:00.0/config \
>     bs=1 seek=4 count=2 conv=notrunc
>   # echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove
> 
> The second command hangs indefinitely without this series; gdb
> confirms the CPU is stuck in vp_reset()'s status-polling loop, with
> vp_modern_get_status() consistently returning 0xff.
> 
> [1] https://syzbot.org/bug?extid=a1c8effc62c569d4bd25
> 
> Abhin Parekadan Jose (2):
>   virtio_pci_modern_dev: warn once on invalid status
>   virtio_pci_modern: avoid infinite loop in vp_reset() on invalid status
> 
>  drivers/virtio/virtio_pci_modern.c     |  6 +++++-
>  drivers/virtio/virtio_pci_modern_dev.c |  8 +++++++-
>  include/uapi/linux/virtio_config.h     | 16 ++++++++++++++++
>  3 files changed, 28 insertions(+), 2 deletions(-)
> 
> --
> 2.51.1