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 0ECDBC433EF for ; Fri, 8 Oct 2021 13:05:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E02A661038 for ; Fri, 8 Oct 2021 13:05:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242353AbhJHNHZ (ORCPT ); Fri, 8 Oct 2021 09:07:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34684 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242404AbhJHNHX (ORCPT ); Fri, 8 Oct 2021 09:07:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633698324; 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=uVQFfb3vAI1ijnE0WV4b+1ZIo0UnTqYUbSmbQDcQl2M=; b=FUYCXp8hVa7g2rVhBToq6abVu04FuZ44PlRkGb7rL5k79rMhM6+PMTVas3l/k7YmZuEIxm EgEH7Ettnr25pl8xRH8J3S2KHp5Sdk9UmgI0kt8YWTsWcPK7T2nD2YkqyDr/fx/za+rbhD GrsEZ81pK1PVjZZ+zpsKIUB7jAlhBTs= Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-133-6gqYpz3XO-mxG3W4Q52PNg-1; Fri, 08 Oct 2021 09:05:10 -0400 X-MC-Unique: 6gqYpz3XO-mxG3W4Q52PNg-1 Received: by mail-ed1-f70.google.com with SMTP id p13-20020a056402044d00b003db3256e4f2so9202043edw.3 for ; Fri, 08 Oct 2021 06:05:10 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=uVQFfb3vAI1ijnE0WV4b+1ZIo0UnTqYUbSmbQDcQl2M=; b=yq8x7PiQ9Lk+Zp8kil+uGUDg0k6nzLfZySmbih3iipvuI2dGmx838ReOt4fE38NztD XKbSBzMmPgr6ZMpz1G554iCDcFiLlaNfNNEE0DCtPFjao7E8el58fjksH+vU3OJPMXf5 Z0/+ghgMrxqghDm/33mxSse7cZAaqhaegunqoAOMR0Oh75p5iMadmoObHU9PNDwMe5F8 YcCKoQ3CG72HZ3QmkJlpPYML/oJdP96klAtFluKz4r0kxufgGkRra6rr7l41z6tMR2mJ Rv/qEZnWZLvFpGSYG/jo8lhi1or30KPM60/X/Mu82362oI9SD5oaqhxDururYZlc1evC 7Tkw== X-Gm-Message-State: AOAM533xIboaq+AjdRNG5LpCEoS4MFkbL8+HMovuWljPnZQMvMojfByn cOQo5OOKECEUXZuQUG1jCZ/dszWeeU6Eiz4eRSceOYvYh3Vgm3bdZEQYSbVv7AXYrKFJ8rvHXKs 9b/hOpkWE0KwbBuYr X-Received: by 2002:a17:906:368c:: with SMTP id a12mr4208930ejc.143.1633698308456; Fri, 08 Oct 2021 06:05:08 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwlxA2f9rNxTHQq8IKY2BJh4lL9hMx84StuoKNUlOgnyNlZwYvMbH6zVdMCXYXCN5WHfEx88w== X-Received: by 2002:a17:906:368c:: with SMTP id a12mr4208897ejc.143.1633698308147; Fri, 08 Oct 2021 06:05:08 -0700 (PDT) Received: from redhat.com ([2.55.132.170]) by smtp.gmail.com with ESMTPSA id c10sm898413eje.37.2021.10.08.06.05.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Oct 2021 06:05:07 -0700 (PDT) Date: Fri, 8 Oct 2021 09:05:03 -0400 From: "Michael S. Tsirkin" To: Halil Pasic Cc: Jason Wang , Xie Yongji , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, markver@us.ibm.com, Cornelia Huck , Christian Borntraeger , linux-s390@vger.kernel.org, stefanha@redhat.com, Raphael Norwitz , qemu-devel@nongnu.org Subject: Re: [PATCH v2 1/1] virtio: write back F_VERSION_1 before validate Message-ID: <20211008085839-mutt-send-email-mst@kernel.org> References: <20211008123422.1415577-1-pasic@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211008123422.1415577-1-pasic@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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. > > 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. 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 finalize_features config op for this. It's not enough to address vhost user and vhost block devices since these do not get the features until 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. > > 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 > -- > 2.25.1