On 02/04, Mina Almasry wrote:
On Tue, Feb 4, 2025 at 10:06 AM Stanislav Fomichev stfomichev@gmail.com wrote:
On 02/04, Mina Almasry wrote:
On Tue, Feb 4, 2025 at 4:32 AM Paolo Abeni pabeni@redhat.com wrote:
On 2/3/25 11:39 PM, Mina Almasry wrote:
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.
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/ 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?
I don't run into any issues with those unmaps in place, but I'm running x86 with iommu bypass (and as you mention in the other thread, those calls are no-ops in this case).