Merge tag 'mlx5-updates-2022-09-27' of git://git.kernel.org/pub/scm/linux/kernel...

Merge tag 'mlx5-updates-2022-09-27' of git://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux

Saeed Mahameed says:

====================
mlx5-updates-2022-09-27

This is Part #1 of 4 parts series to align mlx5's implementation of
XSK (AF_XDP) RX-Qs indexing and management with other vendors:

Maxim Says:
===========

xsk: Bug fixes for frame mapping on striding RQ

Striding RQ relies on the driver mapping RX buffers into the NIC's
virtual memory space. Currently, regadless of the XSK frame size, mlx5e
maps them using MTT, and each mapping's length is PAGE_SIZE. As the
result, the stride size used by striding RQ is also equal to PAGE_SIZE.

This decision has the following issues:

1. In the XSK aligned mode with frame size smaller than PAGE_SIZE, it's
suboptimal. Using 2K strides and 2K pages allows to post twice as fewer
WQEs.

2. MTT is not suitable for unaligned frames, as it requires natural
alignment theoretically, in practice at least 8-byte alignment.

3. Using mapping and stride bigger than the frame has risk of writing
over the bounds of the XSK frame upon receiving packets bigger than MTU,
which is possible in some specific configurations.

This series addresses issues 1 and 2 and alleviates issue 3. Where
possible, page and stride size will match the XSK frame size (firmware
upgrade may be needed to have effect for 2K frames). Unaligned mode will
use KSM instead of MTT, which allows to drop the partial workaround [1].

[1]: https://lore.kernel.org/netdev/YufYFQ6JN91lQbso@boxer/T/
====================

Link: https://lore.kernel.org/r/20220927203611.244301-1-saeed@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>