On 2019-01-11 10:37 p.m., Yu Zhao wrote: > On Fri, Jan 11, 2019 at 04:27:44PM +0100, Michel Dänzer wrote: >> On 2019-01-10 6:56 p.m., Przemek Socha wrote: >>> >>> [ 147.846148] [drm:amdgpu_display_user_framebuffer_create [amdgpu]] Invalid >>> pitch: expecting 10752 but got 10624 >>> [ 147.846155] [drm:drm_internal_framebuffer_create] could not create >>> framebuffer" >> >> Thanks, this confirms that the check is too strict. I've sent a patch >> reverting this as well. >> >> >> Yu, I like the idea behind your changes, but unfortunately it's more >> complicated than that. If you want to work on similar checks which >> accurately reflect the hardware constraints, people on the amd-gfx list >> should be able to help with that. > > Hi Michel, sorry for the troubles. No worries, I missed these issues as well in my review. > Background: after we turned on iommu with amd_iommu=force_isolation, > we saw io page faults from amd gpu (stoney ridge). We tracked it > down to userspace using 32-pixel pitch alignment, which seems smaller > than the minimum alignment supported by the hw. If that was the case, the corresponding surface would be displayed badly distorted, because the hardware would use a different pitch. > Instead of rejecting the alignment, we suspect, it uses 64-pixel > alignment to do dma. Actually, it's more likely that it would use the next smaller well-aligned pitch, as it would probably simply ignore the least significant bits smaller than the minimum alignment. > The larger alignment sometimes causes out of bound memory accesses, thus > the io page faults. Per the above, this is more likely due to insufficient alignment of the vertical size of the surface, resulting in the allocated memory being too small. > 1) how do properly validate pitch alignment passed to kernel space? It's pretty complicated, I'm afraid. A case-insensitive search for "display" in https://gitlab.freedesktop.org/mesa/mesa/tree/master/src/amd/addrlib might serve to give an idea of the complexity. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
