Am 2021-04-29 um 12:21 p.m. schrieb Andrey Grodzovsky: > > > On 2021-04-29 12:15 p.m., Felix Kuehling wrote: >> Am 2021-04-29 um 12:04 p.m. schrieb Andrey Grodzovsky: >>> So as I understand your preferred approach is that I scope any >>> back_end, HW specific function with drm_dev_enter/exit because that >>> where MMIO >>> access takes place. But besides explicit MMIO access thorough >>> register accessors in the HW back-end there is also indirect MMIO >>> access >>> taking place throughout the code in the driver because of various VRAM >>> BOs which provide CPU access to VRAM through the VRAM BAR. This kind of >>> access is spread all over in the driver and even in mid-layers such as >>> TTM and not limited to HW back-end functions. It means it's much harder >>> to spot such places to surgically scope them with drm_dev_enter/exit >>> and >>> also that any new such code introduced will immediately break hot >>> unplug >>> because the developers can't be expected to remember making their code >>> robust to this specific use case. That why when we discussed internally >>> what approach to take to protecting code with drm_dev_enter/exit we >>> opted for using the widest available scope. >> >> VRAM can also be mapped in user mode. Is there anything preventing user >> mode from accessing the memory after unplug? I guess the best you could >> do is unmap it from the CPU page table and let the application segfault >> on the next access. Or replace the mapping with a dummy page in system >> memory? > > We indeed unmap but instead of letting it segfault insert dummy page on > the next page fault. See here > https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=drm-misc-next&id=6dde3330ffa450e2e6da4d19e2fd0bb94b66b6ce > And I am aware that this doesn't take care of KFD user mapping. > As you know, we had some discussions with you on this topic and it's on > my TODO list to follow up on this to solve it for KFD too. ROCm user mode maps VRAM BOs using render nodes. So I'd expect ttm_bo_vm_dummy_page to work for KFD as well. I guess we'd need something special for KFD's doorbell and MMIO (HDP flush) mappings. Was that the discussion about the file address space? Regards, Felix > > Andrey > >> >> Regards, >> Felix >> >> >>> >>> Andrey _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
