[DPDK/vhost/virtio Bug 1658] Vhost multi-queue reconnection failed with QEMU version 4.2.0 to 5.1.0

[DPDK/vhost/virtio Bug 1658] Vhost multi-queue reconnection failed with QEMU version 4.2.0 to 5.1.0

[bugzilla]

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https://bugs.dpdk.org/show_bug.cgi?id=1658

            Bug ID: 1658
           Summary: Vhost multi-queue reconnection failed with QEMU
                    version 4.2.0 to 5.1.0
           Product: DPDK
           Version: 18.11
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: vhost/virtio
          Assignee: dev@dpdk.org
          Reporter: nandinipersad361@gmail.com
  Target Milestone: ---

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. QEMU-5.2.0 fixes this issue in commit f66337bdbfda
(“vhost-user: save features of multiqueues if chardev is closed”).

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).

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