From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EAC82CEACEF for ; Mon, 17 Nov 2025 15:07:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vL0oX-0008Fu-5n; Mon, 17 Nov 2025 10:06:46 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vL0oH-0008Aj-9L for qemu-devel@nongnu.org; Mon, 17 Nov 2025 10:06:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vL0oE-0007zO-UQ for qemu-devel@nongnu.org; Mon, 17 Nov 2025 10:06:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763391984; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CcHHiAIlek2OQ7wCAHq6FwESlWvQEuYq9D//bdLJmZ0=; b=HgyTy1elK5vY9tod38byfc+LaJ9hZ8F0OhRs/vpBNXzUrYD7pybXaT4YOtC6LnoYhI6fIo vHaf1lX54+AtXjfI3DcsbdxYQ6KEeaVGDig2ePsZ4WQigzdHAeRECpCOySXqynku0Kg09V r/WgP9u7Ezy49dtZUQlEQrSZ+4KnxXM= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-301-vkOkfeglPBOWPKuzGfrsCQ-1; Mon, 17 Nov 2025 10:06:21 -0500 X-MC-Unique: vkOkfeglPBOWPKuzGfrsCQ-1 X-Mimecast-MFC-AGG-ID: vkOkfeglPBOWPKuzGfrsCQ_1763391980 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 587F21955D59; Mon, 17 Nov 2025 15:06:18 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.112]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 67416180049F; Mon, 17 Nov 2025 15:06:16 +0000 (UTC) Date: Mon, 17 Nov 2025 15:06:12 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: qemu-devel@nongnu.org, Jason Wang , Andrew Melnychenko , Yuri Benditovich Subject: Re: ebpf functions can fail without setting an error Message-ID: References: <87ectns27j.fsf@pond.sub.org> <87sehfsife.fsf@pond.sub.org> <871plwpxpu.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <871plwpxpu.fsf@pond.sub.org> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Nov 17, 2025 at 02:58:37PM +0100, Markus Armbruster wrote: > Markus Armbruster writes: > > > Daniel P. Berrangé writes: > > > >> On Thu, Aug 07, 2025 at 03:14:56PM +0200, Markus Armbruster wrote: > >>> Three functions in ebpf_rss.h take an Error ** argument and return bool. > >>> Good. > >>> > >>> They can all fail without setting an error. Not good. > >>> > >>> The failures without error are: > >>> > >>> * All three stubs in ebpf_rss-stub.c always. Oversight? > >> > >> Opps, yes, we really should have added error_setg() calls for diagnosis > >> if someone tries to use eBPF when QEMU build has it disabled. > > Easy enough, but... > > > Some stubs exist only to mollify the linker. They are not meant to be > > called. They should abort(), optionally with lipstick. > > > > Other stubs are called and should fail nicely. > > > > Can you tell me offhand which kind these are? > > If calling these stubs is possible, I'd like to know how I can get them > called, so I can test the errors I add. > > If calling is not possible, I'd rather add abort()s. > > I tried to figure out whether calling is possible, but it ended in > confusion. Can you help? * ebpf_rss_set_all Is called from virtio_net_attach_ebpf_rss The call is unreachable if ebpf_rss_is_loaded returns false Stub for ebpf_rss_is_loaded always returns false => ebpf_rss_set_all stub is unreachable * ebpf_rss_load_fds, ebpf_rss_load Is called from virtio_net_load_ebpf_fds, which is called from virtio_net_load_ebpf The call to virtio_net_load_ebpf_fds is unreachable if virtio_net_attach_ebpf_to_backend fails virtio_net_attach_ebpf_to_backend fails if set_steering_ebpf fails set_steering_ebpf fails if ioctl(fd, TUNSETSTEERINGEBPF...) fails on Linux; all non-Linux impls of ebpf_rss_load_fds return -1 It is theoretically p9ossible to build QEMU without EBPF while both glibc & the kernel support TUNSETSTEERINGEBPF ioctl => ebpf_rss_load_fds, ebpf_rss_load are reachable in stubs > >>> * Non-stub ebpf_rss_load() when ebpf_rss_is_loaded(). Are these > >>> reachable? > >> > >> This scenario should never happen, and we should add a call like > >> > >> error_setg(errp, "eBPF program is already loaded"); > >> > >> to report it correctly. > > > > Is it a programming error when it happens? > > This question is still open as well. I'd consider it a programming error. I don't think we have a code path that could trigger it currently. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|