[dpdk-dev] [PATCH v2] vhost: enable reply-ack systematically

[Maxime Coquelin <maxime.coquelin@redhat.com>]

As announced during v20.05 release cycle, this
patch makes reply-ack protocol feature to be enabled
unconditionally.

This protocol feature makes the communication between the
master and the slave more robust, avoiding for example
possible undefined behaviour with VHOST_USER_SET_MEM_TABLE.

Also, reply-ack support will be required for upcoming
VHOST_USER_SET_STATUS request.

Note that this protocol feature was disabled by default
because Qemu version 2.7.0 to 2.9.0 had a bug causing a
deadlock when reply-ack was negotiated and multiqueue
enabled. These Qemu version are now very old and no more
maintained, so we can resonnably consider we no more
support them.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

v2:
 - Fix commit message
 - Remove mention to the workaround in the doc

 doc/guides/prog_guide/vhost_lib.rst | 5 -----
 lib/librte_vhost/vhost_user.c       | 9 ---------
 2 files changed, 14 deletions(-)

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index 07e40e3c5e..db921f922b 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -104,11 +104,6 @@ The following is an overview of some key Vhost API functions:
     from accessing memory the virtio device isn't allowed to, when the feature
     is negotiated and an IOMMU device is declared.
 
-    However, this feature enables vhost-user's reply-ack protocol feature,
-    which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
-    Enabling this flag with these Qemu version results in Qemu being blocked
-    when multiple queue pairs are declared.
-
   - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
 
     Postcopy live-migration support will be enabled when this flag is set.
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 84bebad792..ea9cd107b9 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -2012,15 +2012,6 @@ vhost_user_get_protocol_features(struct virtio_net **pdev,
 	rte_vhost_driver_get_features(dev->ifname, &features);
 	rte_vhost_driver_get_protocol_features(dev->ifname, &protocol_features);
 
-	/*
-	 * REPLY_ACK protocol feature is only mandatory for now
-	 * for IOMMU feature. If IOMMU is explicitly disabled by the
-	 * application, disable also REPLY_ACK feature for older buggy
-	 * Qemu versions (from v2.7.0 to v2.9.0).
-	 */
-	if (!(features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)))
-		protocol_features &= ~(1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK);
-
 	msg->payload.u64 = protocol_features;
 	msg->size = sizeof(msg->payload.u64);
 	msg->fd_num = 0;
-- 
2.26.2