On Tue, Feb 4, 2025 at 10:06 AM Stanislav Fomichev [off-list ref] wrote:

On 02/04, Mina Almasry wrote:

quoted

On Tue, Feb 4, 2025 at 4:32 AM Paolo Abeni [off-list ref] wrote:

quoted

On 2/3/25 11:39 PM, Mina Almasry wrote:

quoted

The TX path had been dropped from the Device Memory TCP patch series
post RFCv1 [1], to make that series slightly easier to review. This
series rebases the implementation of the TX path on top of the
net_iov/netmem framework agreed upon and merged. The motivation for
the feature is thoroughly described in the docs & cover letter of the
original proposal, so I don't repeat the lengthy descriptions here, but
they are available in [1].

Sending this series as RFC as the winder closure is immenient. I plan on
reposting as non-RFC once the tree re-opens, addressing any feedback
I receive in the meantime.

I guess you should drop this paragraph.

quoted

Full outline on usage of the TX path is detailed in the documentation
added in the first patch.

Test example is available via the kselftest included in the series as well.

The series is relatively small, as the TX path for this feature largely
piggybacks on the existing MSG_ZEROCOPY implementation.

It looks like no additional device level support is required. That is
IMHO so good up to suspicious level :)

It is correct no additional device level support is required. I don't
have any local changes to my driver to make this work. I think Stan
on-list was able to run the TX path (he commented on fixes to the test
but didn't say it doesn't work :D) and one other person was able to
run it offlist.

For BRCM I had shared this: https://lore.kernel.org/netdev/ZxAfWHk3aRWl-F31@mini-arch/ (local)
I have similar internal patch for mlx5 (will share after RX part gets
in). I agree that it seems like gve_unmap_packet needs some work to be more
careful to not unmap NIOVs (if you were testing against gve).

Hmm. I think you're right. We ran into a similar issue with the RX
path. The RX path worked 'fine' on initial merge, but it was passing
dmabuf dma-addrs to the dma-mapping API which Jason later called out
to be unsafe. The dma-mapping API calls with dmabuf dma-addrs will
boil down into no-ops for a lot of setups I think which is why I'm not
running into any issues in testing, but upon closer look, I think yes,
we need to make sure the driver doesn't end up passing these niov
dma-addrs to functions like dma_unmap_*() and dma_sync_*().

Stan, do you run into issues (crashes/warnings/bugs) in your setup
when the driver tries to unmap niovs? Or did you implement these
changes purely for safety?

Let me take a deeper look here and suggest something for the next
version. I think we may indeed need the driver to declare that it can
handle niovs in the TX path correctly (i.e. not accidentally pass niov
dma-addrs to the dma-mapping API).

--
Thanks,
Mina