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 3DF26C433F5 for ; Fri, 8 Oct 2021 15:09:54 +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 8AE4D6101A for ; Fri, 8 Oct 2021 15:09:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 8AE4D6101A 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]:41998 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYrVQ-0003SU-Pe for qemu-devel@archiver.kernel.org; Fri, 08 Oct 2021 11:09:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36650) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYrUQ-0002mN-Cv for qemu-devel@nongnu.org; Fri, 08 Oct 2021 11:08:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41216) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYrUO-00082Z-Mk for qemu-devel@nongnu.org; Fri, 08 Oct 2021 11:08:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633705726; 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=PUCyJf0CD/kcfrq7C8GdCqWYBNHc0A3utB2YFlkZ+S0=; b=EXIkvoZbUDjt0SdLXAwf6457T0L3GHlHF0C7MfPrWe4euWw4CsMoWotWD5zopiCd3zopgo zt+VCsTBleqheYvQeoqVcjrT5wCS8GPptYDZI6zv/14cgbd3tN47eWrGlJzs66/5cJnaxk FP1JSPEqyNvXTm55WZg8VrAwnFPXjDk= 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-477-Q5UmhENRNISgc1ByGcD4Ig-1; Fri, 08 Oct 2021 11:08:45 -0400 X-MC-Unique: Q5UmhENRNISgc1ByGcD4Ig-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 48617814615; Fri, 8 Oct 2021 15:08:37 +0000 (UTC) Received: from localhost (unknown [10.39.193.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9CBE65BAF4; Fri, 8 Oct 2021 15:08:13 +0000 (UTC) From: Cornelia Huck To: Halil Pasic , "Michael S. Tsirkin" Subject: Re: [PATCH v2 1/1] virtio: write back F_VERSION_1 before validate In-Reply-To: <20211008155156.626e78b5.pasic@linux.ibm.com> Organization: Red Hat GmbH References: <20211008123422.1415577-1-pasic@linux.ibm.com> <20211008085839-mutt-send-email-mst@kernel.org> <20211008155156.626e78b5.pasic@linux.ibm.com> User-Agent: Notmuch/0.32.1 (https://notmuchmail.org) Date: Fri, 08 Oct 2021 17:08:11 +0200 Message-ID: <87ily7y2p0.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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=-0.051, 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, Christian Borntraeger , qemu-devel@nongnu.org, Jason Wang , linux-kernel@vger.kernel.org, stable@vger.kernel.org, virtualization@lists.linux-foundation.org, Halil Pasic , Xie Yongji , stefanha@redhat.com, Raphael Norwitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Oct 08 2021, Halil Pasic wrote: > On Fri, 8 Oct 2021 09:05:03 -0400 > "Michael S. Tsirkin" wrote: > >> On Fri, Oct 08, 2021 at 02:34:22PM +0200, 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: "... the driver MAY read (but MUST >> > NOT write) the device-specific configuration fields to check that it can >> > support the device ..." before setting FEATURES_OK. >> > >> > 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 a regression so let's try to address >> >> actually, regressions. and we can add >> "since originally before validate callback existed >> config space was only read after >> FEATURES_OK. See Fixes tags for relevant commits" >> >> > it. > > How about replacing the paragraph above with the following? > > "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. Before validate callback existed, config space was only > read after FEATURES_OK. However, we already have two regression, so > let's address this here as well." >> > >> > 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. > > and add > "See Fixes tags for relevant commits." > here. >> >> Let's add a work around description now: >> >> >> For QEMU, we can work around the issue by writing out the features >> register with VIRTIO_F_VERSION_1 bit set. We (ab) use the > s/features register/feature bits/ > rationale: ccw does not have a features register, and qemu does not > really act as if its behavior was controlled by the values in a features > register. I.e. when we read the register we see VIRTIO_F_VERSION_! > because the feature is offered. In QEMU we basically read host_featues > but write the guest_features. And what drives device behavior is mostly > guest_features. > > s/(ab) use/(ab)use/ > >> finalize_features config op for this. It's not enough to address vhost > > s/It's/This is/ > >> user and vhost block devices since these do not get the features until > > s/vhost user and vhost block/some vhost-user and vhost-vdpa/ ? > > Ratioale: I think vhost block is just a vhost-user device. On the other > hand vhost-user-fs works like charm because the config space is > implemented in qemu and not in the vhost-user device. I > didn't check vhost_net. I'm not even sure qemu offers a vhost_net > implementation. Anyway I wouldn't like to make any false statements here. > >> FEATURES_OK, however it looks like these two actually never handled the >> endian-ness for legacy mode correctly, so at least that's not a >> regression. >> >> No devices except virtio net and virtio blk seem to be affected. >> >> Long term the right thing to do is to fix the hypervisors. >> > > Sounds good. Thanks! Are you OK with my changes proposed to your changes? > > Regards, > Halil >> >> > >> > Cc: #v4.11 >> > 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 | 11 +++++++++++ >> > 1 file changed, 11 insertions(+) >> > >> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c >> > index 0a5b54034d4b..236081afe9a2 100644 >> > --- a/drivers/virtio/virtio.c >> > +++ b/drivers/virtio/virtio.c >> > @@ -239,6 +239,17 @@ 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 config space accesses before >> > FEATURES_OK for >> > + * these when needed. >> > + */ >> > + if (drv->validate && !virtio_legacy_is_little_endian() >> > + && device_features & >> > BIT_ULL(VIRTIO_F_VERSION_1)) { >> > + 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 >> > >> > base-commit: 60a9483534ed0d99090a2ee1d4bb0b8179195f51 FWIW, with the amends: Reviewed-by: Cornelia Huck