userspace-tso: Document the minimum kernel version.

The kernel needs to be at least 4.19-rc7 to include the commit
9d2f67e43b73 ("net/packet: fix packet drop as of virtio gso")
otherwise the TSO packets are dropped when using raw sockets.

Fixes: 29cf9c1b3b9c ("userspace: Add TCP Segmentation Offload support")
Reported-by: Yi Yang <yangyi01@inspur.com>
Signed-off-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

diff --git a/Documentation/topics/userspace-tso.rst b/Documentation/topics/userspace-tso.rst
index aafa4a1bf2c610ec5b483d8023efe40eea26a500..14a7c6fb381d1aaf452d54aea6389729c18bd581 100644 (file)
--- a/Documentation/topics/userspace-tso.rst
+++ b/Documentation/topics/userspace-tso.rst
@@ -104,6 +104,12 @@ on ports without TSO support.  That also means guests using vhost-user
 in client mode will receive TSO packet regardless of TSO being enabled
 or disabled within the guest.
 
+All kernel devices that use the raw socket interface (veth, for example)
+require the kernel commit 9d2f67e43b73 ("net/packet: fix packet drop as of
+virtio gso") in order to work properly. This commit was merged in upstream
+kernel 4.19-rc7, so make sure your kernel is either newer or contains the
+backport.
+
 ~~~~~~~~~~~~~~~~~~
 Performance Tuning
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