On 18/10/2018 22:46, Andy Lutomirski wrote: >> [0] drivers/usb/gadget/function/f_fs.c::ffs_user_copy_worker() >> >> Sebastian > I think we need an entirely new API: > > user_mm_ctx_t ctx = user_mm_ctx_get(); > > ... > > use_user_mm_ctx(ctx); > unuse_user_mm_ctx(ctx); > > ... > > user_mm_ctx_put(ctx); > > and ctx will store a copy of mm and PKRU. > That looks like a good API in general. The ffs_user_copy_worker that Sebastian mentioned seems to be used by AIO, in which case of course it has to happen in a kernel thread. But while the API is good, deciding on the desired semantics is "interesting". The submitting thread might be changing PKRU between the time the I/O operation is submitted and the time it is completed, for example. You could look up the task's PKRU at use_mm time, except that the task might have disappeared... In the end just using PKRU=0 makes some sense and it only should be documented that some kernel services will ignore PKRU. Paolo
