2021年12月14日(火) 17:54 Christian König <christian.koenig@xxxxxxx>: > > Am 13.12.21 um 12:18 schrieb Shunsuke Mie: > > 2021年12月10日(金) 22:29 Christian König <christian.koenig@xxxxxxx>: > >> Am 10.12.21 um 14:26 schrieb Jason Gunthorpe: > >>> On Fri, Dec 10, 2021 at 01:47:37PM +0100, Christian König wrote: > >>>> Am 10.12.21 um 13:42 schrieb Jason Gunthorpe: > >>>>> On Fri, Dec 10, 2021 at 08:29:24PM +0900, Shunsuke Mie wrote: > >>>>>> Hi Jason, > >>>>>> Thank you for replying. > >>>>>> > >>>>>> 2021年12月8日(水) 2:14 Jason Gunthorpe <jgg@xxxxxxxx>: > >>>>>>> On Fri, Dec 03, 2021 at 12:51:44PM +0900, Shunsuke Mie wrote: > >>>>>>>> Hi maintainers, > >>>>>>>> > >>>>>>>> Could you please review this patch series? > >>>>>>> Why is it RFC? > >>>>>>> > >>>>>>> I'm confused why this is useful? > >>>>>>> > >>>>>>> This can't do copy from MMIO memory, so it shouldn't be compatible > >>>>>>> with things like Gaudi - does something prevent this? > >>>>>> I think if an export of the dma-buf supports vmap, CPU is able to access the > >>>>>> mmio memory. > >>>>>> > >>>>>> Is it wrong? If this is wrong, there is no advantages this changes.. > >>>>> I don't know what the dmabuf folks did, but yes, it is wrong. > >>>>> > >>>>> IOMEM must be touched using only special accessors, some platforms > >>>>> crash if you don't do this. Even x86 will crash if you touch it with > >>>>> something like an XMM optimized memcpy. > >>>>> > >>>>> Christian? If the vmap succeeds what rules must the caller use to > >>>>> access the memory? > >>>> See dma-buf-map.h and especially struct dma_buf_map. > >>>> > >>>> MMIO memory is perfectly supported here and actually the most common case. > >>> Okay that looks sane, but this rxe RFC seems to ignore this > >>> completely. It stuffs the vaddr directly into a umem which goes to all > >>> manner of places in the driver. > >>> > >>> ?? > >> Well, yes that can go boom pretty quickly. > > Sorry, I was wrong. The dma_buf_map treats both iomem and vaddr region, but > > this RFC only supports vaddr. Advantage of the partial support is we can use the > > vaddr dma-buf in RXE without changing a rxe data copy implementation. > > Well that is most likely not a good idea. > > For example buffers for GPU drivers can be placed in both MMIO memory > and system memory. > > If you don't want to provoke random failures you *MUST* be able to > handle both if you want to use this. I agree with you. I'll add the support and resubmit patch series. Thanks a lot, Shunsuke. > > Regards, > Christian. > > > > > An example of a dma-buf pointing to a vaddr is some gpu drivers use RAM for > > VRAM and we can get dma-buf for the region that indicates vaddr regions. > > Specifically, the gpu driver using gpu/drm/drm_gem_cma_helper.c is one such > > example. > > > >> Not sure what they want to use this for. > > I'd like to use RDMA with RXE for that memory region. > > > > Best, > > Shunsuke > >> Christian. > >> > >>> Jason >
