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 49C4DC433EF for ; Fri, 8 Oct 2021 15:43:53 +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 AB6426101E for ; Fri, 8 Oct 2021 15:43:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org AB6426101E 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]:49056 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mYs2J-00033L-FK for qemu-devel@archiver.kernel.org; Fri, 08 Oct 2021 11:43:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43424) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYs0q-0001md-Dt for qemu-devel@nongnu.org; Fri, 08 Oct 2021 11:42:20 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:44533) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mYs0l-0002NK-GH for qemu-devel@nongnu.org; Fri, 08 Oct 2021 11:42:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633707730; 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=qMC5Klotg1aJNEk7elIqSRCi23Sna03uJX/agMDIgxg=; b=hfG3zom7+tWBYTRUDnC3e7/50qouLfw3ciRb2G5ZG0Kn38JGdJz5/rc9MTxIgLHoBcb8mo oRDpLvVzxVl4W+8LJ9OexglyqZc9n7xXkcb7b4HtmCOa0rcb6oDUKdGLCaBitA8KaTFizC e4rTYcqPJv4F8jp7yNFVg7+x8gk1w40= 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-195-icog4bE6M_Gx649Q2OVUIg-1; Fri, 08 Oct 2021 11:42:09 -0400 X-MC-Unique: icog4bE6M_Gx649Q2OVUIg-1 Received: by mail-ed1-f70.google.com with SMTP id f4-20020a50e084000000b003db585bc274so3979210edl.17 for ; Fri, 08 Oct 2021 08:42:09 -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=qMC5Klotg1aJNEk7elIqSRCi23Sna03uJX/agMDIgxg=; b=a9HRtiRF6tl/ra/wLDJfEvXczgp33L+fVZjPkLHs3vQ0kH5TcnjZJYhh0zMKSArX2P K/53h4IqaQb64lKGERwAZpTz5YDyHfpHenXZzZQyskBBsBSXfILwygZ5DYTxNAaXnGV1 9wSd0PgylsMeScXPbw6YdwZD9c7uVojk2dXeom/yRJV9H6cIPrGhbUkPHOAEaMdNe2DX p7fdY6Lh9R8ReKe+Pel3RkqQWQx8DUrDrUTfJYxQ0xffFTSZnyzRTstMpnMTWxjene2I s6A840Xbhup+Krk9w8zXRmVAREMsH1X4QbutytI9xZYSgwQrEn9laOz6CgewJVZvEP0z bjCg== X-Gm-Message-State: AOAM5321FGOXlKzK+mEqwALDeQPKZmbfe06XrGDg1ylzJA8GlYFGZLR7 I6OwFTS68VJdkzXYFs/37JaZ4Dq395bcVi1n55tyFWeTJ2jDA9OnULTlgMl+8Yalo79fekaJu9y bG8j6FtBJo3obuJ8= X-Received: by 2002:a50:da04:: with SMTP id z4mr15752286edj.52.1633707728445; Fri, 08 Oct 2021 08:42:08 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwHLSNoBYozNsq5483RYGKOQ6xoIu8y6Sysra7Dpoor+71RjKofWVLel+TDlQXhZNhKirsgbQ== X-Received: by 2002:a50:da04:: with SMTP id z4mr15752226edj.52.1633707728015; Fri, 08 Oct 2021 08:42:08 -0700 (PDT) Received: from redhat.com ([2.55.132.170]) by smtp.gmail.com with ESMTPSA id m9sm1193458edl.66.2021.10.08.08.42.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Oct 2021 08:42:07 -0700 (PDT) Date: Fri, 8 Oct 2021 11:42:02 -0400 From: "Michael S. Tsirkin" To: Halil Pasic Subject: Re: [PATCH v2 1/1] virtio: write back F_VERSION_1 before validate Message-ID: <20211008113904-mutt-send-email-mst@kernel.org> References: <20211008123422.1415577-1-pasic@linux.ibm.com> <20211008085839-mutt-send-email-mst@kernel.org> <20211008155156.626e78b5.pasic@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: <20211008155156.626e78b5.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 03:51:56PM +0200, 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, two regressions > 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/ ? Let's just say "not enough to address vhost devices since some of these etc" > 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. it does > Anyway I wouldn't like to make any false statements here. ok > > 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 yes. > > > > > > > > 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 > >