On Thu, 20 Apr 2023 07:13:49 -0700, Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > On Wed, 19 Apr 2023 23:19:22 -0700 Christoph Hellwig wrote: > > > In this case yes, pinned user memory, it gets sliced up into MTU sized > > > chunks, fed into an Rx queue of a device, and user can see packets > > > without any copies. > > > > How long is the life time of these mappings? Because dma_map_* > > assumes a temporary mapping and not one that is pinned bascically > > forever. > > Yeah, this one is "for ever". > > > > Quite similar use case #2 is upcoming io_uring / "direct placement" > > > patches (former from Meta, latter for Google) which will try to receive > > > just the TCP data into pinned user memory. > > > > I don't think we can just long term pin user memory here. E.g. for > > confidential computing cases we can't even ever do DMA straight to > > userspace. I had that conversation with Meta's block folks who > > want to do something similar with io_uring and the only option is an > > an allocator for memory that is known DMAable, e.g. through dma-bufs. > > > > You guys really all need to get together and come up with a scheme > > that actually works instead of piling these hacks over hacks. > > Okay, that simplifies various aspects. We'll just used dma-bufs from > the start in the new APIs. I am not particularly familiar with dma-bufs. I want to know if this mechanism can solve the problem of virtio-net. I saw this framework, allowing the driver do something inside the ops of dma-bufs. If so, is it possible to propose a new patch based on dma-bufs? Thanks.
