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 60859C4332F for ; Fri, 8 Oct 2021 15:42:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B40E6101A for ; Fri, 8 Oct 2021 15:42:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243167AbhJHPoR (ORCPT ); Fri, 8 Oct 2021 11:44:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:36066 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243253AbhJHPoI (ORCPT ); Fri, 8 Oct 2021 11:44:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633707732; 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=LheI2rZPsKyjhYyVufP/VpIKOIBgzd61yVEj0C0lcKTmgI0XJajKogvkq3PQeHxB3zIa7B t9t0Ov9iTrYNu0u6eBoap01jopYIniRbbh9+Nx3OQalcoacTUOEFW/kchgDNG/g/k4lW0M PNERTQuNKj6Y1umgIyZn29IHDg0hldc= 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-205-Cev0GczyPGOuERw5LTDUyA-1; Fri, 08 Oct 2021 11:42:09 -0400 X-MC-Unique: Cev0GczyPGOuERw5LTDUyA-1 Received: by mail-ed1-f70.google.com with SMTP id c8-20020a50d648000000b003daa53c7518so9522811edj.21 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=4QZciEH/CBpWFoDwdChivuh9KGxd3KfWrrX+9qjW2B+oNq9BhFm6Sth1oL+B9QeQv1 KuPYpSdkWFF24gQwPA4K2U9DI3QDJTMerAJvjbFi2Pe7aZVudc/IcTubGKCvOxkc0ZzO 76bVBX1EBnOndDjepqqae0SF0I5qyMQLmtK3aiN1plUyBCozd/DfS1XR6+Une5v94Drk jvhly4qwjbWR75s8ra3pgeEPwppZqfloAq+4s4FXS2ji2srTQOazZPHadKKxRZjV+EFv sbt2Q3PWSeM36iKXxWgA13Z4V5c57veQOE5Bv8QowP/6iNiQboiZf6rpNBDCjPgxwW/z ICGA== X-Gm-Message-State: AOAM532amW9VniLUoVFgE8A5RQSu7TtlzBfYExcVRhRuAXavo3zw2UVL 4hrd59G0o49jE8w0sZC/1xa4KVCrQROajlm376ChlwpV+gsp8XVdFXnl+/GD/6zlcJoB0wpg5W+ MC+68/UGORciiamBt X-Received: by 2002:a50:da04:: with SMTP id z4mr15752278edj.52.1633707728421; 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 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: <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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211008155156.626e78b5.pasic@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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 > >