From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5B25B63B6 for ; Fri, 11 Aug 2023 15:09:39 +0000 (UTC) Received: from mail-oa1-f51.google.com (mail-oa1-f51.google.com [209.85.160.51]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 394D4171F; Fri, 11 Aug 2023 08:09:38 -0700 (PDT) Received: by mail-oa1-f51.google.com with SMTP id 586e51a60fabf-1a28de15c8aso1766413fac.2; Fri, 11 Aug 2023 08:09:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1691766577; x=1692371377; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=debaR9w83oy3hy7pUMTqrCGw8R8d+IK8qQ6gmlwHI6E=; b=j+dNrUsMR0gbBJmqLl6vS7qOcY9VBHi+e7Zym12MklQnkXtabIQNq01xv8d4YVJvsv gzC9/Pfz6jFDroxizEiCmJvopmMrK3FDUvaeILXfO2nEIPml7PaWRahQ5u+nysryg5Aw voO5NG8ffW30ENC9xoop8IQyTDQpZoeyKo4IF51Kz+g8MK068VRIx+iZeLimvg/aUFzw kKR2e3SNE/Iwkbd4aknLGUGKkWa4ejKLwLXcnRkZbPqAmnHb6YqOcXFw0o5uSlCyaelC 6mqhMra985OrnwI1Wn48d581NHVGX1BMr6LkBRMbiONXviI23g8pqNFdwR+j0DN7WMZF YfNQ== X-Gm-Message-State: AOJu0YzXtPizTSWP0qIneFHq7pda4ydaw4CpdueAIG3q43Ll5QlW7/Up mvVsOR6CSzehk8kpJLvCy3I= X-Google-Smtp-Source: AGHT+IFeGwTh9IZhXRWR8Y++SyaE1HUn3wCocYTxJwLj8RTVcxi5sOkSV1Dq/lqXvwcPGMow1RX4Sg== X-Received: by 2002:a05:6871:1cb:b0:1b0:12d7:1ef6 with SMTP id q11-20020a05687101cb00b001b012d71ef6mr2405364oad.25.1691766577381; Fri, 11 Aug 2023 08:09:37 -0700 (PDT) Received: from maniforge ([24.1.27.177]) by smtp.gmail.com with ESMTPSA id p188-20020a0dcdc5000000b00583f8f41cb8sm1048301ywd.63.2023.08.11.08.09.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Aug 2023 08:09:37 -0700 (PDT) Date: Fri, 11 Aug 2023 10:09:34 -0500 From: David Vernet To: Yonghong Song Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, tj@kernel.org, clm@meta.com, thinker.li@gmail.com Subject: Re: [PATCH bpf-next] bpf: Support default .validate() and .update() behavior for struct_ops links Message-ID: <20230811150934.GA542801@maniforge> References: <20230810220456.521517-1-void@manifault.com> <371c72e1-f2b7-8309-0329-cdffc8a3f98d@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <371c72e1-f2b7-8309-0329-cdffc8a3f98d@linux.dev> User-Agent: Mutt/2.2.10 (2023-03-25) X-Spam-Status: No, score=-1.4 required=5.0 tests=BAYES_00, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Thu, Aug 10, 2023 at 11:43:26PM -0700, Yonghong Song wrote: > > > On 8/10/23 3:04 PM, David Vernet wrote: > > Currently, if a struct_ops map is loaded with BPF_F_LINK, it must also > > define the .validate() and .update() callbacks in its corresponding > > struct bpf_struct_ops in the kernel. Enabling struct_ops link is useful > > in its own right to ensure that the map is unloaded if an application > > crashes. For example, with sched_ext, we want to automatically unload > > the host-wide scheduler if the application crashes. We would likely > > never support updating elements of a sched_ext struct_ops map, so we'd > > have to implement these callbacks showing that they _can't_ support > > element updates just to benefit from the basic lifetime management of > > struct_ops links. > > > > Let's enable struct_ops maps to work with BPF_F_LINK even if they > > haven't defined these callbacks, by assuming that a struct_ops map > > element cannot be updated by default. > > Maybe you want to add one map_flag to indicate validate/update callbacks > are optional for a struct_ops link? In this case, some struct_ops maps > can still require validate() and update(), but others can skip them? Are you proposing that a map flag be added that a user space caller can specify to say that they're OK with a struct_ops implementation not supporting .validate() and .update(), but still want to use a link to manage registration and unregistration? Assuming I'm understanding your suggestion correctly, I don't think it's what we want. Updating a struct_ops map value is arguably orthogonal to the bpf link handling registration and unregistration, so it seems confusing to require a user to specify that it's the behavior they want as there's no reason they shouldn't want it. If they mistakenly thought that update element is supposed for that struct_ops variant, they'll just get an -EOPNOTSUPP error at runtime, which seems reasonable. If a struct_ops implementation should have implemented .validate() and/or .update() and neglects to, that would just be a bug in the struct_ops implementation. Apologies if I've misunderstood your proposal, and please feel free to clarify if I have. Thanks, David > > > > > Signed-off-by: David Vernet > > --- > > kernel/bpf/bpf_struct_ops.c | 17 +++++++++++------ > > 1 file changed, 11 insertions(+), 6 deletions(-) > > > > diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c > > index eaff04eefb31..3d2fb85186a9 100644 > > --- a/kernel/bpf/bpf_struct_ops.c > > +++ b/kernel/bpf/bpf_struct_ops.c > > @@ -509,9 +509,12 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key, > > } > > if (st_map->map.map_flags & BPF_F_LINK) { > > - err = st_ops->validate(kdata); > > - if (err) > > - goto reset_unlock; > > + err = 0; > > + if (st_ops->validate) { > > + err = st_ops->validate(kdata); > > + if (err) > > + goto reset_unlock; > > + } > > set_memory_rox((long)st_map->image, 1); > > /* Let bpf_link handle registration & unregistration. > > * > > @@ -663,9 +666,6 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) > > if (attr->value_size != vt->size) > > return ERR_PTR(-EINVAL); > > - if (attr->map_flags & BPF_F_LINK && (!st_ops->validate || !st_ops->update)) > > - return ERR_PTR(-EOPNOTSUPP); > > - > > t = st_ops->type; > > st_map_size = sizeof(*st_map) + > > @@ -838,6 +838,11 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map > > goto err_out; > > } > > + if (!st_map->st_ops->update) { > > + err = -EOPNOTSUPP; > > + goto err_out; > > + } > > + > > err = st_map->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data); > > if (err) > > goto err_out;