On Thu, 17 Dec 2020 21:45:06 +0800, Robin Murphy wrote: > > On 2020-12-17 10:25, Christian König wrote: > > Am 17.12.20 um 02:07 schrieb Chen Li: > >> On Wed, 16 Dec 2020 22:19:11 +0800, > >> Christian König wrote: > >>> Am 16.12.20 um 14:48 schrieb Chen Li: > >>>> On Wed, 16 Dec 2020 15:59:37 +0800, > >>>> Christian König wrote: > >>>>> [SNIP] > >>>> Hi, Christian. I'm not sure why this change is a hack here. I cannot see > >>>> the problem and wll be grateful if you give more explainations. > >>> __memset is supposed to work on those addresses, otherwise you can't use the > >>> e8860 on your arm64 system. > >> If __memset is supposed to work on those adresses, why this > >> commit(https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftorvalds%2Flinux%2Fcommit%2Fba0b2275a6781b2f3919d931d63329b5548f6d5f&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274023350%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=HhWxUaLo3WpzoV6hjV%2BG1HICaIOXwsoNpzv5tNMNg8A%3D&reserved=0) > >> is needed? (I also notice drm/radeon didn't take this change though) just out > >> of curiosity. > > > > We generally accept those patches as cleanup in the kernel with the hope that > > we can find a way to work around the userspace restrictions. > > > > But when you also have this issue in userspace then there isn't much we can do > > for you. > > > >>> Replacing the the direct write in the kernel with calls to writel() or > >>> memset_io() will fix that temporary, but you have a more general problem > >>> here. > >> I cannot see what's the more general problem here :( u mean performance? > > > > No, not performance. See standards like OpenGL, Vulkan as well as VA-API and > > VDPAU require that you can mmap() device memory and execute memset/memcpy on > > the memory from userspace. > > > > If your ARM base board can't do that for some then you can't use the hardware > > with that board. > > If the VRAM lives in a prefetchable PCI bar then on most sane Arm-based systems > I believe it should be able to mmap() to userspace with the Normal memory type, > where unaligned accesses and such are allowed, as opposed to the Device memory > type intended for MMIO mappings, which has more restrictions but stricter > ordering guarantees. Hi, Robin. I cannot understand it allow unaligned accesses. prefetchable PCI bar should also be mmio, and accesses will end with device memory, so why does this allow unaligned access? > Regardless of what happens elsewhere though, if something is mapped *into the > kernel* with ioremap(), then it is fundamentally wrong per the kernel memory > model to reference that mapping directly without using I/O accessors. That is > not specific to any individual architecture, and Sparse should be screaming > about it already. I guess in this case the UVD code needs to pay more attention > to whether radeon_bo_kmap() ends up going via ttm_bo_ioremap() or not. > > (I'm assuming the initial fault was memset() with 0 trying to perform "DC ZVA" > on a Device-type mapping from ioremap() - FYI a stacktrace on its own without > the rest of the error dump showing what actually triggered it isn't overly > useful) > > Robin. why it may be 'DC ZVA'? I'm not sure the pc in initial kernel fault memset, but I capture the userspace crash pc: stp(128bit) or str with neon(also 128bit) to render node(/dev/dri/renderD128). > >>>>> For amdgpu I suggest that we allocate the UVD message in GTT instead of > >>>>> VRAM > >>>>> since we don't have the hardware restriction for that on the new > >>>>> generations. > >>>>> > >>>> Thanks, I will try to dig into deeper. But what's the "hardware > >>>> restriction" meaning here? I'm not familiar with video driver stack and amd > >>>> gpu, sorry. > >>> On older hardware (AGP days) the buffer had to be in VRAM (MMIO) memory, but > >>> on > >>> modern system GTT (system memory) works as well. > >> IIUC, e8860 can use amdgpu(I use radeon now) beause its device id 6822 is in > >> amdgpu's table. But I cannot tell whether e8860 has iommu, and I cannot find > >> iommu from lspci, so graphics translation table may not work here? > > > > That is not related to IOMMU. IOMMU is a feature of the CPU/motherboard. This > > is implemented using GTT, e.g. the VM page tables inside the GPU. > > > > And yes it should work I will prepare a patch for it. > > > >>>>> BTW: How does userspace work on arm64 then? The driver stack usually only > >>>>> works > >>>>> if mmio can be mapped directly. > >>>> I also post two usespace issue on mesa, and you may be interested with > >>>> them: > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fmesa%2Fmesa%2F-%2Fissues%2F3954&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274023350%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ZR7pDS%2BCLUuMjCeKcMAXfHtbczt8WdUwSeLZCuHfCHw%3D&reserved=0 > >>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fmesa%2Fmesa%2F-%2Fissues%2F3951&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274033344%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=jAJo3aG2I1oIDTZXWhNgcKoKbd6tTdiAtc7vE4hJJPY%3D&reserved=0 > >>>> I paste some virtual memory map in userspace there. (and the two problems > >>>> do bother me quite a long time.) > >>> I don't really see a solution for those problems. > >>> > >>> See it is perfectly valid for an application to memset/memcpy on mmaped MMIO > >>> space which comes from OpenGL or Vulkan. > >>> > >>> So your CPU simply won't work with the hardware. We could work around that > >>> with > >>> a couple of hacks, but this is a pretty much general problem. > >>> > >>> Regards, > >>> Christian. > >> Thanks! Can you provid some details about these hacks? Should I post another > >> issue on the mail list? > > > > Adjust the kernel and/or user space to never map VRAM to the CPU. > > > > This violates the OpenGL/Vulkan specification in some ways. So not sure if > > that will work or not. > > > > Regards, > > Christian. > > _______________________________________________ > > dri-devel mailing list > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
