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. 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 >
