On Wed, Mar 20, 2024 at 04:18:05PM +0000, Shameerali Kolothum Thodi wrote: > > What I have noticed is that, > -read interface works fine and I can receive struct tiommu_hwpt_pgfault data. > -But once Guest handles the page faults and returns the page response, > the write to fault fd never reaches the kernel. The sequence is like below, > > sqe = io_uring_get_sqe(ring); > io_uring_prep_write(sqe, hwpt->fault_fd, resp, sizeof(*resp), 0); > io_uring_sqe_set_data(sqe, resp); > io_uring_submit(ring); > ret = io_uring_wait_cqe(ring, &cqe); > .... > Please find the function here[2] > > The above cqe wait never returns and hardware times out without receiving > page response. My understanding of io_uring default op is that it tries to > issue an sqe as non-blocking first. But it looks like the above write sequence > ends up in kernel poll_wait() as well.Not sure how we can avoid that for > write. Ah, right, it is because poll can't be choosy about read/write, it has to work equally for both directions. iommufd_fault_fops_poll() never returns EPOLLOUT It should just always return EPOLLOUT because we don't have any queue to manage. Jason
