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 270CAD65C7C for ; Wed, 17 Dec 2025 17:24:17 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vVvFU-0006ns-OO; Wed, 17 Dec 2025 12:23:40 -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 1vVvFB-0006mI-L2 for qemu-arm@nongnu.org; Wed, 17 Dec 2025 12:23:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vVvF8-0007pN-JM for qemu-arm@nongnu.org; Wed, 17 Dec 2025 12:23:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1765992196; 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=KErRrw8HoSMIEg7dGk5gpxPR/xd1fk0v71TFQqAWP+U=; b=ZQwloZ1ADAog3pmKUQeYPbK7Uxbaa0rELGV/KRwVCT0TJuJi25iYhOkzVKfGvv0kwBq2XI qxHZi+R1O6rf4jpLKEKGtzLMoa+iZ7mvt3oMQC/HXZ/oyNCA9TpLLfHaH0sVDd+pfn9sjG TOjCHgnhbi/7p7X6OlXF316ByBFutdQ= 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-304-h2EFjx79Pu2r9Bi9eiLnWQ-1; Wed, 17 Dec 2025 12:23:13 -0500 X-MC-Unique: h2EFjx79Pu2r9Bi9eiLnWQ-1 X-Mimecast-MFC-AGG-ID: h2EFjx79Pu2r9Bi9eiLnWQ_1765992191 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 6403C195FCDD; Wed, 17 Dec 2025 17:23:11 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.217]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C9699180045B; Wed, 17 Dec 2025 17:23:07 +0000 (UTC) Date: Wed, 17 Dec 2025 17:23:04 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Alex =?utf-8?Q?Benn=C3=A9e?= Cc: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , qemu-devel@nongnu.org, "Michael S . Tsirkin" , Eugenio =?utf-8?B?UMOpcmV6?= , Manos Pitsidianakis , devel@lists.libvirt.org, Richard Henderson , Peter Maydell , qemu-arm@nongnu.org, Jason Wang Subject: Re: [PATCH] hw/arm: Deprecate legacy VirtIO devices on big-endian guests Message-ID: References: <20251217140658.89715-1-philmd@linaro.org> <8734592frz.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8734592frz.fsf@draig.linaro.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=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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_SBL_CSS=3.335, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@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-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Wed, Dec 17, 2025 at 05:13:04PM +0000, Alex Bennée wrote: > Daniel P. Berrangé writes: > > > On Wed, Dec 17, 2025 at 03:06:57PM +0100, Philippe Mathieu-Daudé wrote: > >> We couldn't find a way (guest OS with VirtIO drivers) to test > >> a legacy VirtIO device on a ARM vCPU running in big-endian. > >> > >> Deprecate for the v11.0 release, giving 1 year to users who > >> really care to contribute functional tests. > >> > >> Suggested-by: Alex Bennée > >> Signed-off-by: Philippe Mathieu-Daudé > >> --- > >> docs/about/deprecated.rst | 11 +++++++++++ > >> 1 file changed, 11 insertions(+) > >> > >> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst > >> index ac31a2bce42..3a69facb0f1 100644 > >> --- a/docs/about/deprecated.rst > >> +++ b/docs/about/deprecated.rst > >> @@ -515,6 +515,17 @@ It was implemented as a no-op instruction in TCG up to QEMU 9.0, but > >> only with ``-cpu max`` (which does not guarantee migration compatibility > >> across versions). > >> > >> +VirtIO devices > >> +'''''''''''''' > >> + > >> +Legacy VirtIO devices on Big-Endian ARM architecture (since 11.0) > >> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > >> + > >> +There are no functional tests for legacy virtio devices used by ARM > >> +machines running in big-endian order, which makes harder to maintain > >> +the code path while the code base evolve. > > > > Lack of test coverage is not a reason to deprecate something. > > > > We deprecate things we intend to intentionally remove or intentionally > > change in an incompatible manner. > > We also deprecate things that stop us moving the code forward. c.f. the > long process to deprecate 32 bit hosts. IIUC we're intending to actively block the ability to build on 32 bit hosts. IOW, that's still an example of a deprecation where we will intentionally remove some functionality, rather than just an untested usage scenario. > > If something is not tested, that merely means it has lesser quality > > guarantees, and is liable to unintenionally get broken at times. > > > > If we're planning to *intentionally* remove the ability to use > > legacy virtio on big endian, that would be a reason to deprecate. > > If so the deprecation message should say this, not talk about > > missing functional testing. > > As far as I'm aware BE Arm is a very small niche and I'm not even sure > anyone runs BE Arm systems with VirtIO - let alone legacy VirtIO. If > there are people that need this functionality they need to at least make > themselves known. Is there some technical change we're intending to make that will intentionally impact virtio legacy on BE ? ie, if we add the deprecation, then 2 releases later, what is the code change that means we move it from deprecated.rst into removed-features.rst ? 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 :|