Re: [PATCH 14/23] io_uring: add support for bpf requests

[Pavel Begunkov <asml.silence@gmail.com>]

On 5/19/21 3:13 PM, Pavel Begunkov wrote:
> Wire up a new io_uring operation type IORING_OP_BPF, which executes a
> specified BPF program from the registered prog table. It doesn't allow
> to do anything useful for now, no BPF functions are allowed apart from
> basic ones.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c                 | 92 +++++++++++++++++++++++++++++++++++
>  include/uapi/linux/io_uring.h |  1 +
>  2 files changed, 93 insertions(+)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b13cbcd5c47b..20fddc5945f2 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -682,6 +682,11 @@ struct io_unlink {
>  	struct filename			*filename;
>  };
>  
> +struct io_bpf {
> +	struct file			*file;
> +	struct bpf_prog			*prog;
> +};
> +
>  struct io_completion {
>  	struct file			*file;
>  	struct list_head		list;
> @@ -826,6 +831,7 @@ struct io_kiocb {
>  		struct io_shutdown	shutdown;
>  		struct io_rename	rename;
>  		struct io_unlink	unlink;
> +		struct io_bpf		bpf;
>  		/* use only after cleaning per-op data, see io_clean_op() */
>  		struct io_completion	compl;
>  	};
> @@ -875,6 +881,9 @@ struct io_defer_entry {
>  	u32			seq;
>  };
>  
> +struct io_bpf_ctx {
> +};
> +
>  struct io_op_def {
>  	/* needs req->file assigned */
>  	unsigned		needs_file : 1;
> @@ -1039,6 +1048,7 @@ static const struct io_op_def io_op_defs[] = {
>  	},
>  	[IORING_OP_RENAMEAT] = {},
>  	[IORING_OP_UNLINKAT] = {},
> +	[IORING_OP_BPF] = {},
>  };
>  
>  static bool io_disarm_next(struct io_kiocb *req);
> @@ -1070,6 +1080,7 @@ static void io_rsrc_put_work(struct work_struct *work);
>  static void io_req_task_queue(struct io_kiocb *req);
>  static void io_submit_flush_completions(struct io_comp_state *cs,
>  					struct io_ring_ctx *ctx);
> +static void io_bpf_run(struct io_kiocb *req, unsigned int issue_flags);
>  static bool io_poll_remove_waitqs(struct io_kiocb *req);
>  static int io_req_prep_async(struct io_kiocb *req);
>  
> @@ -3931,6 +3942,53 @@ static int io_openat(struct io_kiocb *req, unsigned int issue_flags)
>  	return io_openat2(req, issue_flags);
>  }
>  
> +static int io_bpf_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> +{
> +	struct io_ring_ctx *ctx = req->ctx;
> +	struct bpf_prog *prog;
> +	unsigned int idx;
> +
> +	if (unlikely(ctx->flags & (IORING_SETUP_IOPOLL|IORING_SETUP_SQPOLL)))
> +		return -EINVAL;
> +	if (unlikely(req->flags & (REQ_F_FIXED_FILE | REQ_F_BUFFER_SELECT)))
> +		return -EINVAL;
> +	if (sqe->ioprio || sqe->len || sqe->cancel_flags)
> +		return -EINVAL;
> +	if (sqe->addr)
> +		return -EINVAL;
> +
> +	idx = READ_ONCE(sqe->off);
> +	if (unlikely(idx >= ctx->nr_bpf_progs))
> +		return -EFAULT;
> +	idx = array_index_nospec(idx, ctx->nr_bpf_progs);
> +	prog = ctx->bpf_progs[idx].prog;
> +	if (!prog)
> +		return -EFAULT;
> +
> +	req->bpf.prog = prog;
> +	return 0;
> +}
> +
> +static void io_bpf_run_task_work(struct callback_head *cb)
> +{
> +	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
> +	struct io_ring_ctx *ctx = req->ctx;
> +
> +	mutex_lock(&ctx->uring_lock);
> +	io_bpf_run(req, 0);
> +	mutex_unlock(&ctx->uring_lock);
> +}
> +
> +static int io_bpf(struct io_kiocb *req, unsigned int issue_flags)
> +{
> +	init_task_work(&req->task_work, io_bpf_run_task_work);
> +	if (unlikely(io_req_task_work_add(req))) {
> +		req_ref_get(req);
> +		io_req_task_queue_fail(req, -ECANCELED);
> +	}
> +	return 0;
> +}
> +
>  static int io_remove_buffers_prep(struct io_kiocb *req,
>  				  const struct io_uring_sqe *sqe)
>  {
> @@ -6002,6 +6060,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  		return io_renameat_prep(req, sqe);
>  	case IORING_OP_UNLINKAT:
>  		return io_unlinkat_prep(req, sqe);
> +	case IORING_OP_BPF:
> +		return io_bpf_prep(req, sqe);
>  	}
>  
>  	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
> @@ -6269,6 +6329,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
>  	case IORING_OP_UNLINKAT:
>  		ret = io_unlinkat(req, issue_flags);
>  		break;
> +	case IORING_OP_BPF:
> +		ret = io_bpf(req, issue_flags);
> +		break;
>  	default:
>  		ret = -EINVAL;
>  		break;
> @@ -10303,6 +10366,35 @@ const struct bpf_verifier_ops bpf_io_uring_verifier_ops = {
>  	.is_valid_access	= io_bpf_is_valid_access,
>  };
>  
> +static void io_bpf_run(struct io_kiocb *req, unsigned int issue_flags)
> +{
> +	struct io_ring_ctx *ctx = req->ctx;
> +	struct io_bpf_ctx bpf_ctx;
> +	struct bpf_prog *prog;
> +	int ret = -EAGAIN;
> +
> +	lockdep_assert_held(&req->ctx->uring_lock);
> +
> +	if (unlikely(percpu_ref_is_dying(&ctx->refs) ||
> +		     atomic_read(&req->task->io_uring->in_idle)))
> +		goto done;
> +
> +	memset(&bpf_ctx, 0, sizeof(bpf_ctx));
> +	prog = req->bpf.prog;
> +
> +	if (prog->aux->sleepable) {

Looks forgot to amend, the condition should be inversed.

> +		rcu_read_lock();
> +		bpf_prog_run_pin_on_cpu(req->bpf.prog, &bpf_ctx);
> +		rcu_read_unlock();
> +	} else {
> +		bpf_prog_run_pin_on_cpu(req->bpf.prog, &bpf_ctx);
> +	}
> +
> +	ret = 0;
> +done:
> +	__io_req_complete(req, issue_flags, ret, 0);
> +}
> +
>  SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
>  		void __user *, arg, unsigned int, nr_args)
>  {
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index b450f41d7389..25ab804670e1 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -138,6 +138,7 @@ enum {
>  	IORING_OP_SHUTDOWN,
>  	IORING_OP_RENAMEAT,
>  	IORING_OP_UNLINKAT,
> +	IORING_OP_BPF,
>  
>  	/* this goes last, obviously */
>  	IORING_OP_LAST,
> 

-- 
Pavel Begunkov