[dpdk-dev] [PATCH v4 0/4] Vhost: fix mq=on but VIRTIO_NET_F_MQ not negotiated

[Maxime Coquelin]

Hi,

This fourth revision fixes patch 1 by not returning early in
SET_FEATURE handling if new features bitfield is same as previous
one. Indeed, as reported by Tiwei, in case negotiated features is 0,
it would return early whereas it should set the Vnet header len.
The change consists in returning early when features are equal only
when the device is un running state.
I did not applied Laszlo's Acked-by and Ladi's Tested-by because of
this change. This new iteration has been tested locally using iPXE.

Having QEMU started with mq=on but guest driver not negotiating
VIRTIO_NET_F_MQ feature ends up in the vhost device to never
start. Indeed, more queues are created in the vhost backend than
configured.

Guest drivers known to not advertise the VIRTIO_NET_F_MQ feature are
iPXE and OVMF Virtio-net drivers.

Queues are created because before starting the guest, QEMU sends
VHOST_USER_SET_VRING_CALL requests for all queues declared in QEMU
command line. Also, once Virtio features negotiated, QEMU sends
VHOST_USER_SET_VRING_ENABLE requests to disable all but the first
queue pair.

This series fixes this by destroying all but first queue pair in
the backend if VIRTIO_NET_F_MQ isn't negotiated. First patches
makes sure that VHOST_USER_SET_FEATURES request doesn't change
Virtio features while the device is running, which should never
happen as per the Virtio spec. This helps to make sure vitqueues
aren't destroyed while being processed, but also protect from
other illegal features changes (e.g. VIRTIO_NET_F_MRG_RXBUF).

Changes since v3:
=================
- Fix Virtio features = 0 case (Tiwei)
Changes since v2:
=================
- Patch 2: Rework & fix VQs destruction loop (Laszlo)
Changes since v1:
=================
- Patch 1: shift bits in the right direction (Ladi)

Maxime Coquelin (4):
  vhost: prevent features to be changed while device is running
  vhost: propagate VHOST_USER_SET_FEATURES handling error
  vhost: extract virtqueue cleaning and freeing functions
  vhost: destroy unused virtqueues when multiqueue not negotiated

 lib/librte_vhost/vhost.c      | 22 ++++++++++++----------
 lib/librte_vhost/vhost.h      |  3 +++
 lib/librte_vhost/vhost_user.c | 39 +++++++++++++++++++++++++++++++++++++--
 3 files changed, 52 insertions(+), 12 deletions(-)

-- 
2.14.3