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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88B95C433EF for ; Thu, 7 Oct 2021 15:33:19 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id D946761245 for ; Thu, 7 Oct 2021 15:33:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D946761245 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:48456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYVOX-0006w2-O2 for qemu-devel@archiver.kernel.org; Thu, 07 Oct 2021 11:33:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36952) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYVNp-0006GU-Vg for qemu-devel@nongnu.org; Thu, 07 Oct 2021 11:32:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:20156) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYVNm-0002xT-1q for qemu-devel@nongnu.org; Thu, 07 Oct 2021 11:32:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633620746; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=yNvi96S0n+2jvC4MnP0vGy5ty9dBkyyLjUTIOiS6II8=; b=FI2iEop/b7vTIczEFgK3aaQs1bUKGblbSbqW3arPb+w62IkoFYODctDVQUCOqt84O3FgES s83ruUI6t0zHIFL6VrZCPXa4HtcREQSELCythYADzdAqnnUeD1hB0caivEcqaHtlhEyhIj Huwm9F8NXQPhHiF6ONo8ftk59RcfBog= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-471-9EoZIu35OqWAyFIIe8QSKQ-1; Thu, 07 Oct 2021 11:32:23 -0400 X-MC-Unique: 9EoZIu35OqWAyFIIe8QSKQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5CCEFDF5B10; Thu, 7 Oct 2021 15:25:54 +0000 (UTC) Received: from localhost (unknown [10.39.193.140]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AE3571E65D5; Thu, 7 Oct 2021 15:25:53 +0000 (UTC) From: Cornelia Huck To: Halil Pasic Subject: Re: [PATCH 1/1] virtio: write back F_VERSION_1 before validate In-Reply-To: <20211007163255.61d95513.pasic@linux.ibm.com> Organization: Red Hat GmbH References: <20211006142533.2735019-1-pasic@linux.ibm.com> <875yu9yruv.fsf@redhat.com> <20211007163255.61d95513.pasic@linux.ibm.com> User-Agent: Notmuch/0.32.1 (https://notmuchmail.org) Date: Thu, 07 Oct 2021 17:25:52 +0200 Message-ID: <8735pczwjj.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.05, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390@vger.kernel.org, markver@us.ibm.com, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Jason Wang , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Halil Pasic , Xie Yongji , stefanha@redhat.com, Raphael Norwitz , Christian Borntraeger Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Oct 07 2021, Halil Pasic wrote: > On Thu, 07 Oct 2021 13:52:24 +0200 > Cornelia Huck wrote: > >> On Wed, Oct 06 2021, Halil Pasic wrote: >> >> > The virtio specification virtio-v1.1-cs01 states: Transitional devices >> > MUST detect Legacy drivers by detecting that VIRTIO_F_VERSION_1 has not >> > been acknowledged by the driver. This is exactly what QEMU as of 6.1 >> > has done relying solely on VIRTIO_F_VERSION_1 for detecting that. >> > >> > However, the specification also says: driver MAY read (but MUST NOT >> > write) the device-specific configuration fields to check that it can >> > support the device before setting FEATURES_OK. >> >> Suggest to put the citations from the spec into quotes, so that they are >> distinguishable from the rest of the text. > > For the record: I basically took Michael's description, the one which you > said you prefer, with some minor changes. Well I did look at what the text said, not the details in the formatting... > > This is one of the changes, which renders this a paraphrase and not a > quote. Michael didn't use quotation marks so I was not sure it is was > a word by word quote anyway. It was. But the spec depends on "During this > step" which does not make any sense without the context. That is why I made > the end of step explicit. I still think that would be nicer while using some quotation marks, even if you are just doing a partial quote. In the first paragraph, however, we really should mark the quote properly. It gave me a stop when I first read it. > > I think we are fine without quotation marks. Those who care can read the > spec. > >> >> > >> > In that case, any transitional device relying solely on >> > VIRTIO_F_VERSION_1 for detecting legacy drivers will return data in >> > legacy format. In particular, this implies that it is in big endian >> > format for big endian guests. This naturally confuses the driver which >> > expects little endian in the modern mode. >> > >> > It is probably a good idea to amend the spec to clarify that >> > VIRTIO_F_VERSION_1 can only be relied on after the feature negotiation >> > is complete. However, we already have regression so let's try to address >> >> s/regression/a regression/ >> > > Yes. Was like this in the original. Will change > >> > it. >> >> Maybe mention what the regression is? > > How about the following? > > The regressions affect the VIRTIO_NET_F_MTU feature of virtio-net and the > VIRTIO_BLK_F_BLK_SIZE feature of virtio-blk for BE guests when virtio > 1.0 is used on both sides. The latter renders virtio-blk unusable with > DASD backing, because things simply don't work with the default. Sounds good to me. > >> >> Also mention that we use this workaround for modern on BE only? > > We have that already, don't we. The sentence that starts with "In > particular". The regression description should reinforce that > sufficiently IMHO. No strong opinion here. Anyone else? > >> >> > >> > Signed-off-by: Halil Pasic >> > Fixes: 82e89ea077b9 ("virtio-blk: Add validation for block size in config space") >> > Fixes: fe36cbe0671e ("virtio_net: clear MTU when out of range") >> > Reported-by: markver@us.ibm.com >> > --- >> > drivers/virtio/virtio.c | 10 ++++++++++ >> > 1 file changed, 10 insertions(+) >> > >> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c >> > index 0a5b54034d4b..494cfecd3376 100644 >> > --- a/drivers/virtio/virtio.c >> > +++ b/drivers/virtio/virtio.c >> > @@ -239,6 +239,16 @@ static int virtio_dev_probe(struct device *_d) >> > driver_features_legacy = driver_features; >> > } >> > >> > + /* >> > + * Some devices detect legacy solely via F_VERSION_1. Write >> > + * F_VERSION_1 to force LE for these when needed. >> >> "...to force LE config space accesses before FEATURES_OK for these when >> needed (BE)." >> >> ? > > Can do, but I would rather omit the (BE) at the end. All the conditions > are necessary: > * have validate callback > * device offered VERSION_1 > * virtio legacy is be > Ok, let's use that without the trailing BE. >> >> > + */ >> > + if (drv->validate && !virtio_legacy_is_little_endian() >> > + && BIT_ULL(VIRTIO_F_VERSION_1) & device_features) { >> >> Nit: putting device_features first would read more naturally to me. >> > > Can do. > >> > + dev->features = BIT_ULL(VIRTIO_F_VERSION_1); >> > + dev->config->finalize_features(dev); >> > + } >> > + >> > if (device_features & (1ULL << VIRTIO_F_VERSION_1)) >> > dev->features = driver_features & device_features; >> > else >> >> Patch LGTM. >> >> > > Thanks for having a look. If you are fine with the proposed solution > please tell me, so I can send out a v2. No further comments other than what I wrote above, but maybe others have comments as well?