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? Regards, Felix > > Andrey
