On Tue, Feb 4, 2025 at 10:32 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > On 2/4/25 7:06 PM, Stanislav Fomichev wrote: > > On 02/04, Mina Almasry wrote: > >> On Tue, Feb 4, 2025 at 4:32 AM Paolo Abeni <pabeni@xxxxxxxxxx> 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). > > What happen if an user try to use devmem TX on a device not really > supporting it? Silent data corruption? > So the tx dma-buf binding netlink API will bind the dma-buf to the netdevice. If that fails, the uapi will return failure and devmem tx will not be enabled. If the dma-binding succeeds, then the device can indeed DMA into the dma-addrs in the device. The TX path will dma from the dma-addrs in the device just fine and it need not be aware that the dma-addrs are coming from a device and not from host memory. The only issue that Stan's patches is pointing to, is that the driver will likely be passing these dma-buf addresses into dma-mapping APIs like dma_unmap_*() and dma_sync_*() functions. Those, AFAIU, will be no-ops with dma-buf addresses in most setups, but it's not 100% safe to pass those dma-buf addresses to these dma-mapping APIs, so we should avoid these calls entirely. > Don't we need some way for the device to opt-in (or opt-out) and avoid > such issues? > Yeah, I think likely the driver needs to declare support (i.e. it's not using dma-mapping API with dma-buf addresses). -- Thanks, Mina
