On Mon, Aug 21, 2017 at 11:11 PM, Felix Kuehling <felix.kuehling at amd.com> wrote: > On 2017-08-21 04:01 PM, Jerome Glisse wrote: >>> From this explanation, I think that the user's supplied VA should be >>> tested that its a valid writable area of the user. >>> How do you test for that ? could you point me to such a code in the kernel ? >>> From looking at other drivers that pin host memory, like mellanox nic, >>> they don't do any special testing for the address they receive from >>> the user. >> GUP (get_user_page()) will perform proper check on your behalf. >> I am assuming those driver use GUP. > Ah, ok. I thought you refer to some other check that needs to be done *before* calling get_user_page(). As Felix said, for APU the GPU doesn't need the memory to be pinned and it uses the ATS to access it directly so we don't call get_user_page() or some other function that calls it eventually. On dGPU I guess it would be similar to what is done in most drivers that need to pin user memory, by calling to get_user_page(). Oded > On APUs, the GPU can address memory directly through ATS. So it doesn't > use GUP. The GPU uses the same page tables as the CPU, so uses the same > access bits to check permissions on the fly. > > On dGPU, when we use VRAM for scratch backing, that doesn't use GUP. In > theory it should be possible to use GUP (using our userptr mechanism). > In that case GUP would check the access permissions of the underlying > mapping. > > Regards, > Felix > >> >> Jérôme >
