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 A08A4C433EF for ; Mon, 4 Oct 2021 15:53:17 +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 3B1056137C for ; Mon, 4 Oct 2021 15:53:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3B1056137C 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]:34756 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mXQHE-0008BI-19 for qemu-devel@archiver.kernel.org; Mon, 04 Oct 2021 11:53:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45274) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mXQF6-00061i-El for qemu-devel@nongnu.org; Mon, 04 Oct 2021 11:51:04 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:47979) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mXQF4-0005jg-HF for qemu-devel@nongnu.org; Mon, 04 Oct 2021 11:51:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633362661; 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=wnNQLEGYyuqtuWKutOrdKZyTyV/siDKuhdgiO+cXLTs=; b=MvuVqhcxHVI+Dt9Tu7yVilrRmKA72wNkKX3htNSeMVd4jqwwA4swdnw+gGU2H8rbN3kYwF VodTbb7UK8m/BvcOEgc92POr4sSA6t/RbT0qT7XkxU4YqX58ax1sdpwb0oNkGUjh9HYwKM WU0nxSv8zdZPi1TBAQpazpKR8JRiZ00= 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-504-c0t_ZGP3Pt2ItEdpb_iEag-1; Mon, 04 Oct 2021 11:50:58 -0400 X-MC-Unique: c0t_ZGP3Pt2ItEdpb_iEag-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F25A3824FA6; Mon, 4 Oct 2021 15:50:56 +0000 (UTC) Received: from localhost (unknown [10.39.193.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6C9BB10016FB; Mon, 4 Oct 2021 15:50:45 +0000 (UTC) From: Cornelia Huck To: "Michael S. Tsirkin" Subject: Re: [RFC PATCH 1/1] virtio: write back features before verify In-Reply-To: <20211004110537-mutt-send-email-mst@kernel.org> Organization: Red Hat GmbH References: <20210930012049.3780865-1-pasic@linux.ibm.com> <20210930070444-mutt-send-email-mst@kernel.org> <20211001092125.64fef348.pasic@linux.ibm.com> <20211002055605-mutt-send-email-mst@kernel.org> <87bl452d90.fsf@redhat.com> <20211004090018-mutt-send-email-mst@kernel.org> <875yuc3ln2.fsf@redhat.com> <20211004110537-mutt-send-email-mst@kernel.org> User-Agent: Notmuch/0.32.1 (https://notmuchmail.org) Date: Mon, 04 Oct 2021 17:50:44 +0200 Message-ID: <87wnms23hn.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Received-SPF: pass client-ip=170.10.133.124; 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=-0.066, 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, virtualization@lists.linux-foundation.org, Halil Pasic , Xie Yongji Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: > On Mon, Oct 04, 2021 at 04:33:21PM +0200, Cornelia Huck wrote: >> On Mon, Oct 04 2021, "Michael S. Tsirkin" wrote: >> >> > On Mon, Oct 04, 2021 at 02:19:55PM +0200, Cornelia Huck wrote: >> >> >> >> [cc:qemu-devel] >> >> >> >> On Sat, Oct 02 2021, "Michael S. Tsirkin" wrote: >> >> >> >> > On Fri, Oct 01, 2021 at 09:21:25AM +0200, Halil Pasic wrote: >> >> >> On Thu, 30 Sep 2021 07:12:21 -0400 >> >> >> "Michael S. Tsirkin" wrote: >> >> >> >> >> >> > On Thu, Sep 30, 2021 at 03:20:49AM +0200, Halil Pasic wrote: >> >> >> > > This patch fixes a regression introduced by commit 82e89ea077b9 >> >> >> > > ("virtio-blk: Add validation for block size in config space") and >> >> >> > > enables similar checks in verify() on big endian platforms. >> >> >> > > >> >> >> > > The problem with checking multi-byte config fields in the verify >> >> >> > > callback, on big endian platforms, and with a possibly transitional >> >> >> > > device is the following. The verify() callback is called between >> >> >> > > config->get_features() and virtio_finalize_features(). That we have a >> >> >> > > device that offered F_VERSION_1 then we have the following options >> >> >> > > either the device is transitional, and then it has to present the legacy >> >> >> > > interface, i.e. a big endian config space until F_VERSION_1 is >> >> >> > > negotiated, or we have a non-transitional device, which makes >> >> >> > > F_VERSION_1 mandatory, and only implements the non-legacy interface and >> >> >> > > thus presents a little endian config space. Because at this point we >> >> >> > > can't know if the device is transitional or non-transitional, we can't >> >> >> > > know do we need to byte swap or not. >> >> >> > >> >> >> > Hmm which transport does this refer to? >> >> >> >> >> >> It is the same with virtio-ccw and virtio-pci. I see the same problem >> >> >> with both on s390x. I didn't try with virtio-blk-pci-non-transitional >> >> >> yet (have to figure out how to do that with libvirt) for pci I used >> >> >> virtio-blk-pci. >> >> >> >> >> >> > Distinguishing between legacy and modern drivers is transport >> >> >> > specific. PCI presents >> >> >> > legacy and modern at separate addresses so distinguishing >> >> >> > between these two should be no trouble. >> >> >> >> >> >> You mean the device id? Yes that is bolted down in the spec, but >> >> >> currently we don't exploit that information. Furthermore there >> >> >> is a fat chance that with QEMU even the allegedly non-transitional >> >> >> devices only present a little endian config space after VERSION_1 >> >> >> was negotiated. Namely get_config for virtio-blk is implemented in >> >> >> virtio_blk_update_config() which does virtio_stl_p(vdev, >> >> >> &blkcfg.blk_size, blk_size) and in there we don't care >> >> >> about transitional or not: >> >> >> >> >> >> static inline bool virtio_access_is_big_endian(VirtIODevice *vdev) >> >> >> { >> >> >> #if defined(LEGACY_VIRTIO_IS_BIENDIAN) >> >> >> return virtio_is_big_endian(vdev); >> >> >> #elif defined(TARGET_WORDS_BIGENDIAN) >> >> >> if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { >> >> >> /* Devices conforming to VIRTIO 1.0 or later are always LE. */ >> >> >> return false; >> >> >> } >> >> >> return true; >> >> >> #else >> >> >> return false; >> >> >> #endif >> >> >> } >> >> >> >> >> > >> >> > ok so that's a QEMU bug. Any virtio 1.0 and up >> >> > compatible device must use LE. >> >> > It can also present a legacy config space where the >> >> > endian depends on the guest. >> >> >> >> So, how is the virtio core supposed to determine this? A >> >> transport-specific callback? >> > >> > I'd say a field in VirtIODevice is easiest. >> >> The transport needs to set this as soon as it has figured out whether >> we're using legacy or not. > > Basically on each device config access? Prior to the first one, I think. It should not change again, should it? > >> I guess we also need to fence off any >> accesses respectively error out the device if the driver tries any >> read/write operations that would depend on that knowledge? >> >> And using a field in VirtIODevice would probably need some care when >> migrating. Hm... > > It's just a shorthand to minimize changes. No need to migrate I think. If we migrate in from an older QEMU, we don't know whether we are dealing with legacy or not, until feature negotiation is already done... don't we have to ask the transport?