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Tuneke" , Christian Dietrich References: <8ec8373d406d1fcb41719e641799dcc5c0455db3.1621424513.git.asml.silence@gmail.com> <20210521010752.lky4pz7zipefrfr7@ast-mbp> From: Pavel Begunkov Subject: Re: [PATCH 15/23] io_uring: enable BPF to submit SQEs Message-ID: Date: Fri, 21 May 2021 10:33:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210521010752.lky4pz7zipefrfr7@ast-mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/21/21 2:07 AM, Alexei Starovoitov wrote: > On Wed, May 19, 2021 at 03:13:26PM +0100, Pavel Begunkov wrote: >> >> +BPF_CALL_3(io_bpf_queue_sqe, struct io_bpf_ctx *, bpf_ctx, >> + const struct io_uring_sqe *, sqe, >> + u32, sqe_len) >> +{ >> + struct io_ring_ctx *ctx = bpf_ctx->ctx; >> + struct io_kiocb *req; >> + >> + if (sqe_len != sizeof(struct io_uring_sqe)) >> + return -EINVAL; >> + >> + req = io_alloc_req(ctx); > > that is GFP_KERNEL allocation. > It's only allowed from sleepable bpf progs and further down > there is a correct check for it, so all good. > But submitting sqe is a fundemntal io_uring operation, > so what is the use case for non-sleepable? > In other words why bother? Allow sleepable only and simplify the code? Actual submission may be moved out of BPF, so enabling it for both, but the question I wonder about is what are the plans for sleepable programs? E.g. if it's a marginal features much limited in functionality, e.g. iirc as it's not allowed to use some BPF data types, it may not worth doing. > >> + if (unlikely(!req)) >> + return -ENOMEM; >> + if (!percpu_ref_tryget_many(&ctx->refs, 1)) { >> + kmem_cache_free(req_cachep, req); >> + return -EAGAIN; >> + } >> + percpu_counter_add(¤t->io_uring->inflight, 1); >> + refcount_add(1, ¤t->usage); >> + >> + /* returns number of submitted SQEs or an error */ >> + return !io_submit_sqe(ctx, req, sqe); > > A buggy bpf prog will be able to pass junk sizeof(struct io_uring_sqe) > as 'sqe' here. > What kind of validation io_submit_sqe() does to avoid crashing the kernel? It works on memory rw shared with userspace, so it already assumes the worst > General comments that apply to all patches: > - commit logs are way too terse. Pls expand with details. > - describe new bpf helpers in comments in bpf.h. Just adding them to an enum is not enough. > - selftest/bpf are mandatory for all new bpf features. > - consider bpf_link style of attaching bpf progs. We had enough issues with progs > that get stuck due to application bugs. Auto-detach saves the day more often than not. Thanks for taking a look! I have no idea what bpf_link is, need to check it out -- Pavel Begunkov