On 02/04, Mina Almasry wrote: > 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). netif_skb_features/ndo_features_check seems like a good fit?
