doc: add vhost multi-queue reconnection issue

This patch added known issue for vhost multi-queue reconnection
with virtio-net/virtio-pmd.

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/known_issues.rst
index de07821..5fb7f83 100644 (file)
--- a/doc/guides/rel_notes/known_issues.rst
+++ b/doc/guides/rel_notes/known_issues.rst
@@ -888,3 +888,24 @@ Unsuitable IOVA mode may be picked as the default
 
 **Driver/Module**:
    ALL.
+
+Vhost multi-queue reconnection failed with QEMU version >= 4.2.0
+----------------------------------------------------------------
+
+**Description**
+   It's a QEMU regression bug (bad commit: c6beefd674ff). QEMU only saves
+   acked features for one vhost-net when vhost quits. When vhost reconnects
+   to virtio-net/virtio-pmd in multi-queue situations, the features been
+   set multiple times are not consistent.
+
+**Implication**
+   Vhost cannot reconnect back to virtio-net/virtio-pmd normally.
+
+**Resolution/Workaround**:
+   It is possible to filter the incorrect acked features at vhost-user side.
+
+**Affected Environment/Platform**:
+   ALL.
+
+**Driver/Module**:
+   Virtual Device Poll Mode Driver (PMD).