doc: add vhost multi-queue reconnection issue

[dpdk.git] / doc / guides / rel_notes / known_issues.rst

diff --git a/doc/guides/rel_notes/known_issues.rst b/doc/guides/rel_notes/known_issues.rst
index 276327c..5fb7f83 100644 (file)
--- a/doc/guides/rel_notes/known_issues.rst
+++ b/doc/guides/rel_notes/known_issues.rst
@@ -127,7 +127,7 @@ HPET timers do not work on the Osage customer reference platform
    work correctly, provided the BIOS supports HPET.
 
 **Driver/Module**:
-   ``lib/librte_eal/common/include/rte_cycles.h``
+   ``lib/librte_eal/include/rte_cycles.h``
 
 
 Not all variants of supported NIC types have been used in testing
@@ -861,3 +861,51 @@ AVX-512 support disabled
 
 **Driver/Module**:
     ALL.
+
+
+Unsuitable IOVA mode may be picked as the default
+-------------------------------------------------
+
+**Description**
+   Not all kernel drivers and not all devices support all IOVA modes. EAL will
+   attempt to pick a reasonable default based on a number of factors, but there
+   may be cases where the default may be unsuitable (for example, hotplugging
+   devices using `igb_uio` driver while having picked IOVA as VA mode on EAL
+   initialization).
+
+**Implication**
+   Some devices (hotplugged or otherwise) may not work due to incompatible IOVA
+   mode being automatically picked by EAL.
+
+**Resolution/Workaround**:
+   It is possible to force EAL to pick a particular IOVA mode by using the
+   `--iova-mode` command-line parameter. If conflicting requirements are present
+   (such as one device requiring IOVA as PA and one requiring IOVA as VA mode),
+   there is no workaround.
+
+**Affected Environment/Platform**:
+   Linux.
+
+**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).