On Mon, Feb 11, 2019 at 8:01 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
> If we have fixed user buffers, we can map them into the kernel when we
> setup the io_uring. That avoids the need to do get_user_pages() for
> each and every IO.
>
> To utilize this feature, the application must call io_uring_register()
> after having setup an io_uring instance, passing in
> IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer to
> an iovec array, and the nr_args should contain how many iovecs the
> application wishes to map.
>
> If successful, these buffers are now mapped into the kernel, eligible
> for IO. To use these fixed buffers, the application must use the
> IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
> set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
> must point to somewhere inside the indexed buffer.
>
> The application may register buffers throughout the lifetime of the
> io_uring instance. It can call io_uring_register() with
> IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
> buffers, and then register a new set. The application need not
> unregister buffers explicitly before shutting down the io_uring
> instance.
>
> It's perfectly valid to setup a larger buffer, and then sometimes only
> use parts of it for an IO. As long as the range is within the originally
> mapped region, it will work just fine.
>
> For now, buffers must not be file backed. If file backed buffers are
> passed in, the registration will fail with -1/EOPNOTSUPP. This
> restriction may be relaxed in the future.
>
> RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
> arbitrary 1G per buffer size is also imposed.
>
> Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
[...]
> static void io_sq_wq_submit_work(struct work_struct *work)
> {
> struct io_kiocb *req = container_of(work, struct io_kiocb, work);
> struct sqe_submit *s = &req->submit;
> const struct io_uring_sqe *sqe = s->sqe;
> struct io_ring_ctx *ctx = req->ctx;
> - mm_segment_t old_fs = get_fs();
> + mm_segment_t old_fs;
> + bool needs_user;
> int ret;
>
> /* Ensure we clear previously set forced non-block flag */
> req->flags &= ~REQ_F_FORCE_NONBLOCK;
> req->rw.ki_flags &= ~IOCB_NOWAIT;
>
> - if (!mmget_not_zero(ctx->sqo_mm)) {
> - ret = -EFAULT;
> - goto err;
> - }
> -
> - use_mm(ctx->sqo_mm);
> - set_fs(USER_DS);
> - s->has_user = true;
> s->needs_lock = true;
> + s->has_user = false;
> +
> + /*
> + * If we're doing IO to fixed buffers, we don't need to get/set
> + * user context
> + */
> + needs_user = io_sqe_needs_user(s->sqe);
> + if (needs_user) {
> + if (!mmget_not_zero(ctx->sqo_mm)) {
> + ret = -EFAULT;
> + goto err;
> + }
> + use_mm(ctx->sqo_mm);
> + old_fs = get_fs();
> + set_fs(USER_DS);
> + s->has_user = true;
> + }
>
> do {
> ret = __io_submit_sqe(ctx, req, s, false, NULL);
> @@ -1011,9 +1110,11 @@ static void io_sq_wq_submit_work(struct work_struct *work)
> cond_resched();
> } while (1);
>
> - set_fs(old_fs);
> - unuse_mm(ctx->sqo_mm);
> - mmput(ctx->sqo_mm);
> + if (needs_user) {
> + set_fs(old_fs);
> + unuse_mm(ctx->sqo_mm);
> + mmput(ctx->sqo_mm);
> + }
> err:
> if (ret) {
> io_cqring_add_event(ctx, sqe->user_data, ret, 0);
> @@ -1308,6 +1409,197 @@ static unsigned long ring_pages(unsigned sq_entries, unsigned cq_entries)
> return (bytes + PAGE_SIZE - 1) / PAGE_SIZE;
> }
>
> +static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
> +{
> + int i, j;
> +
> + if (!ctx->user_bufs)
> + return -ENXIO;
> +
> + for (i = 0; i < ctx->nr_user_bufs; i++) {
> + struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
> +
> + for (j = 0; j < imu->nr_bvecs; j++)
> + put_page(imu->bvec[j].bv_page);
> +
> + if (ctx->account_mem)
> + io_unaccount_mem(ctx->user, imu->nr_bvecs);
> + kfree(imu->bvec);
> + imu->nr_bvecs = 0;
> + }
> +
> + kfree(ctx->user_bufs);
> + ctx->user_bufs = NULL;
> + ctx->nr_user_bufs = 0;
> + return 0;
> +}
[...]
> +static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
> + unsigned nr_args)
> +{
> + struct vm_area_struct **vmas = NULL;
> + struct page **pages = NULL;
> + int i, j, got_pages = 0;
> + int ret = -EINVAL;
> +
> + if (ctx->user_bufs)
> + return -EBUSY;
> + if (!nr_args || nr_args > UIO_MAXIOV)
> + return -EINVAL;
> +
> + ctx->user_bufs = kcalloc(nr_args, sizeof(struct io_mapped_ubuf),
> + GFP_KERNEL);
> + if (!ctx->user_bufs)
> + return -ENOMEM;
> +
> + for (i = 0; i < nr_args; i++) {
> + struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
> + unsigned long off, start, end, ubuf;
> + int pret, nr_pages;
> + struct iovec iov;
> + size_t size;
> +
> + ret = io_copy_iov(ctx, &iov, arg, i);
> + if (ret)
> + break;
> +
> + /*
> + * Don't impose further limits on the size and buffer
> + * constraints here, we'll -EINVAL later when IO is
> + * submitted if they are wrong.
> + */
> + ret = -EFAULT;
> + if (!iov.iov_base || !iov.iov_len)
> + goto err;
> +
> + /* arbitrary limit, but we need something */
> + if (iov.iov_len > SZ_1G)
> + goto err;
> +
> + ubuf = (unsigned long) iov.iov_base;
> + end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + start = ubuf >> PAGE_SHIFT;
> + nr_pages = end - start;
> +
> + if (ctx->account_mem) {
> + ret = io_account_mem(ctx->user, nr_pages);
> + if (ret)
> + goto err;
> + }
> +
> + ret = 0;
> + if (!pages || nr_pages > got_pages) {
Nit: No need to check for `!pages` as long as `pages` and `got_pages`
are synchronized (which guarantees that `!pages` implies
`got_pages==0`).
> + kfree(vmas);
> + kfree(pages);
> + pages = kmalloc_array(nr_pages, sizeof(struct page *),
> + GFP_KERNEL);
> + vmas = kmalloc_array(nr_pages,
> + sizeof(struct vma_area_struct *),
typo: s/vma_area_struct/vm_area_struct/
> + GFP_KERNEL);
> + if (!pages || !vmas) {
> + ret = -ENOMEM;
> + if (ctx->account_mem)
> + io_unaccount_mem(ctx->user, nr_pages);
> + goto err;
> + }
> + got_pages = nr_pages;
> + }
> +
> + imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
> + GFP_KERNEL);
> + ret = -ENOMEM;
> + if (!imu->bvec) {
> + if (ctx->account_mem)
> + io_unaccount_mem(ctx->user, nr_pages);
> + goto err;
> + }
> +
> + ret = 0;
> + down_read(¤t->mm->mmap_sem);
> + pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE,
> + pages, vmas);
> + if (pret == nr_pages) {
> + /* don't support file backed memory */
> + for (j = 0; j < nr_pages; j++) {
> + struct vm_area_struct *vma = vmas[j];
> +
> + if (vma->vm_file &&
> + !is_file_hugepages(vma->vm_file)) {
> + ret = -EOPNOTSUPP;
> + break;
> + }
> + }
> + } else {
> + ret = pret < 0 ? pret : -EFAULT;
> + }
> + up_read(¤t->mm->mmap_sem);
> + if (ret) {
> + /*
> + * if we did partial map, or found file backed vmas,
> + * release any pages we did get
> + */
> + if (pret > 0) {
> + for (j = 0; j < pret; j++)
> + put_page(pages[j]);
> + }
> + if (ctx->account_mem)
> + io_unaccount_mem(ctx->user, nr_pages);
> + goto err;
> + }
> +
> + off = ubuf & ~PAGE_MASK;
> + size = iov.iov_len;
> + for (j = 0; j < nr_pages; j++) {
> + size_t vec_len;
> +
> + vec_len = min_t(size_t, size, PAGE_SIZE - off);
> + imu->bvec[j].bv_page = pages[j];
> + imu->bvec[j].bv_len = vec_len;
> + imu->bvec[j].bv_offset = off;
> + off = 0;
> + size -= vec_len;
> + }
> + /* store original address for later verification */
> + imu->ubuf = ubuf;
> + imu->len = iov.iov_len;
> + imu->nr_bvecs = nr_pages;
> + }
> + kfree(pages);
> + kfree(vmas);
> + ctx->nr_user_bufs = nr_args;
> + return 0;
> +err:
> + kfree(pages);
> + kfree(vmas);
> + io_sqe_buffer_unregister(ctx);
io_sqe_buffer_unregister() gets rid of elements up to
ctx->nr_user_bufs, but as far as I can tell, ctx->nr_user_bufs is
always zero here. I think that's going to cause a reference leak.
> + return ret;
> +}
