Hi Jens, Thanks for responding. On Wed, May 24, 2023 at 8:06 AM Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 5/23/23 8:48?PM, Jeff Xu wrote: > > Hi > > I have a question on the protection key in io_uring. Today, when a > > user thread enters the kernel through syscall, PKRU is preserved, and > > the kernel will respect the PKEY protection of memory. > > > > For example: > > sys_mprotect_pkey((void *)ptr, size, PROT_READ | PROT_WRITE, pkey); > > pkey_write_deny(pkey); <-- disable write access to pkey for this thread. > > ret = read(fd, ptr, 1); <-- this will fail in the kernel. > > > > I wonder what is the case for io_uring, since read is now async, will > > kthread have the user thread's PKUR ? > > There is no kthread. What can happen is that some operation may be > punted to the io-wq workers, but these act exactly like a thread created > by the original task. IOW, if normal threads retain the protection key, > so will any io-wq io_uring thread. If they don't, they do not. > Does this also apply to when the IORING_SETUP_SQPOLL [1] flag is used ? it mentions a kernel thread is created to perform submission queue polling. [1] https://manpages.debian.org/unstable/liburing-dev/io_uring_setup.2.en.html#IORING_SETUP_SQPOLL > > In theory, it is possible, i.e. from io_uring_enter syscall. But I > > don't know the implementation details of io_uring, hence asking the > > expert in this list. > > Right, if the IO is done inline, then it won't make a difference if eg > read(2) is used or IORING_OP_READ (or similar) with io_uring. > Can you please clarify what "IO is done inline" means ? i.e. are there cases that are not inline ? Thanks! -Jeff > -- > Jens Axboe >
