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 98A1EC433F5 for ; Fri, 8 Oct 2021 13:07:07 +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 0015761037 for ; Fri, 8 Oct 2021 13:07:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0015761037 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]:57144 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYpab-0007vU-Mf for qemu-devel@archiver.kernel.org; Fri, 08 Oct 2021 09:07:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40138) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYpZ5-00074q-LA for qemu-devel@nongnu.org; Fri, 08 Oct 2021 09:05:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:54657) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYpZ1-0001uF-EQ for qemu-devel@nongnu.org; Fri, 08 Oct 2021 09:05:30 -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-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-195-HIZJoiFENUy7Erl28Tmcrg-1; Fri, 08 Oct 2021 09:05:09 -0400 X-MC-Unique: HIZJoiFENUy7Erl28Tmcrg-1 Received: by mail-ed1-f72.google.com with SMTP id h19-20020aa7de13000000b003db6ad5245bso501943edv.9 for ; Fri, 08 Oct 2021 06:05:09 -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=658i9aArvzqW4xExMpZ9mcO2OWZuWO4AYURkMaSqKRXWLgWWVWtteRSyY3gkX9sj4+ N6hy4MTXO8F4XNDsjog8787F06B8R5N91M8uGaBh4rOemv84u0AD/PrvKqbKHlbpKePg +uuqFjVj8QHBqt+0bamURSrVmt/X72A9YamZXmJX0tRJsYgpM83QY61upQC4aX8u+bRv eILj4WEdKkLTwmff0MKAjdffDAPM72R+lXMVAJfMdWgIqHcYgGPK80rtgaWhGdr4Np71 LvNLaDaZrofh6J1bIKe187Ey2FZHFFzQMs86TI3bCoQWPcYWXEe9ITMKQisUJtiouheY ULKg== X-Gm-Message-State: AOAM532pQ1p3kJffH2ZZi38srG6RKcimqJp5YkSBZj8wyzBa93XyYMoe nKfaQoTHPWMfWNiatbWPSP1l9uj+JC3/zg/UvJoLmk+xNdulUcfez9qVUQeZ8W7qhfRv7bsEz4C VIyp3Sc6QLIxtyQw= X-Received: by 2002:a17:906:368c:: with SMTP id a12mr4208932ejc.143.1633698308460; 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 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 In-Reply-To: <20211008123422.1415577-1-pasic@linux.ibm.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@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 , Cornelia Huck , linux-kernel@vger.kernel.org, stable@vger.kernel.org, virtualization@lists.linux-foundation.org, 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 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