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 X-Spam-Level: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CDD3CC433E6 for ; Tue, 23 Feb 2021 02:05:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 879D064E20 for ; Tue, 23 Feb 2021 02:05:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231483AbhBWCFt (ORCPT ); Mon, 22 Feb 2021 21:05:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23315 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231431AbhBWCFj (ORCPT ); Mon, 22 Feb 2021 21:05:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614045851; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+6idrDlv3jxmFr3UwSuJjfWfYYHRXCR4c1yPFc4Gx68=; b=CzKhP9zGRk8xZjzEqxTk1EHQm/Pqm5sWINRoWwPe/kvJCLoQVNe188EzkZrTjT2T2dPLWj aND4s93HWCaNcVXjQocpQjpbprMTSty3BZPeec3J0+OyrwixtT2rbd2ACoRCAGLwsvCR1T QzoCvPdvXjBTtYuPMr91P3WXoBnU4f0= 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-551-LStuIhLXPKaUwoKYNmhnqA-1; Mon, 22 Feb 2021 21:04:06 -0500 X-MC-Unique: LStuIhLXPKaUwoKYNmhnqA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 759C310082F6; Tue, 23 Feb 2021 02:04:05 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-58.pek2.redhat.com [10.72.13.58]) by smtp.corp.redhat.com (Postfix) with ESMTP id 356865B4A0; Tue, 23 Feb 2021 02:03:58 +0000 (UTC) Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero To: Si-Wei Liu , "Michael S. Tsirkin" Cc: elic@nvidia.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org References: <1613735698-3328-1-git-send-email-si-wei.liu@oracle.com> <605e7d2d-4f27-9688-17a8-d57191752ee7@redhat.com> <20210222023040-mutt-send-email-mst@kernel.org> <22fe5923-635b-59f0-7643-2fd5876937c2@oracle.com> From: Jason Wang Message-ID: Date: Tue, 23 Feb 2021 10:03:57 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <22fe5923-635b-59f0-7643-2fd5876937c2@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2021/2/23 9:12 上午, Si-Wei Liu wrote: > > > On 2/21/2021 11:34 PM, Michael S. Tsirkin wrote: >> On Mon, Feb 22, 2021 at 12:14:17PM +0800, Jason Wang wrote: >>> On 2021/2/19 7:54 下午, Si-Wei Liu wrote: >>>> Commit 452639a64ad8 ("vdpa: make sure set_features is invoked >>>> for legacy") made an exception for legacy guests to reset >>>> features to 0, when config space is accessed before features >>>> are set. We should relieve the verify_min_features() check >>>> and allow features reset to 0 for this case. >>>> >>>> It's worth noting that not just legacy guests could access >>>> config space before features are set. For instance, when >>>> feature VIRTIO_NET_F_MTU is advertised some modern driver >>>> will try to access and validate the MTU present in the config >>>> space before virtio features are set. >>> >>> This looks like a spec violation: >>> >>> " >>> >>> The following driver-read-only field, mtu only exists if >>> VIRTIO_NET_F_MTU is >>> set. >>> This field specifies the maximum MTU for the driver to use. >>> " >>> >>> Do we really want to workaround this? >>> >>> Thanks >> And also: >> >> The driver MUST follow this sequence to initialize a device: >> 1. Reset the device. >> 2. Set the ACKNOWLEDGE status bit: the guest OS has noticed the device. >> 3. Set the DRIVER status bit: the guest OS knows how to drive the >> device. >> 4. Read device feature bits, and write the subset of feature bits >> understood by the OS and driver to the >> device. During this step the driver MAY read (but MUST NOT write) the >> device-specific configuration >> fields to check that it can support the device before accepting it. >> 5. Set the FEATURES_OK status bit. The driver MUST NOT accept new >> feature bits after this step. >> 6. Re-read device status to ensure the FEATURES_OK bit is still set: >> otherwise, the device does not >> support our subset of features and the device is unusable. >> 7. Perform device-specific setup, including discovery of virtqueues >> for the device, optional per-bus setup, >> reading and possibly writing the device’s virtio configuration space, >> and population of virtqueues. >> 8. Set the DRIVER_OK status bit. At this point the device is “live”. >> >> >> so accessing config space before FEATURES_OK is a spec violation, right? > It is, but it's not relevant to what this commit tries to address. I > thought the legacy guest still needs to be supported. > > Having said, a separate patch has to be posted to fix the guest driver > issue where this discrepancy is introduced to virtnet_validate() > (since commit fe36cbe067). But it's not technically related to this > patch. > > -Siwei I think it's a bug to read config space in validate, we should move it to virtnet_probe(). Thanks > >> >> >>>> Rejecting reset to 0 >>>> prematurely causes correct MTU and link status unable to load >>>> for the very first config space access, rendering issues like >>>> guest showing inaccurate MTU value, or failure to reject >>>> out-of-range MTU. >>>> >>>> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 >>>> devices") >>>> Signed-off-by: Si-Wei Liu >>>> --- >>>>    drivers/vdpa/mlx5/net/mlx5_vnet.c | 15 +-------------- >>>>    1 file changed, 1 insertion(+), 14 deletions(-) >>>> >>>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c >>>> b/drivers/vdpa/mlx5/net/mlx5_vnet.c >>>> index 7c1f789..540dd67 100644 >>>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c >>>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c >>>> @@ -1490,14 +1490,6 @@ static u64 mlx5_vdpa_get_features(struct >>>> vdpa_device *vdev) >>>>        return mvdev->mlx_features; >>>>    } >>>> -static int verify_min_features(struct mlx5_vdpa_dev *mvdev, u64 >>>> features) >>>> -{ >>>> -    if (!(features & BIT_ULL(VIRTIO_F_ACCESS_PLATFORM))) >>>> -        return -EOPNOTSUPP; >>>> - >>>> -    return 0; >>>> -} >>>> - >>>>    static int setup_virtqueues(struct mlx5_vdpa_net *ndev) >>>>    { >>>>        int err; >>>> @@ -1558,18 +1550,13 @@ static int mlx5_vdpa_set_features(struct >>>> vdpa_device *vdev, u64 features) >>>>    { >>>>        struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev); >>>>        struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev); >>>> -    int err; >>>>        print_features(mvdev, features, true); >>>> -    err = verify_min_features(mvdev, features); >>>> -    if (err) >>>> -        return err; >>>> - >>>>        ndev->mvdev.actual_features = features & >>>> ndev->mvdev.mlx_features; >>>>        ndev->config.mtu = cpu_to_mlx5vdpa16(mvdev, ndev->mtu); >>>>        ndev->config.status |= cpu_to_mlx5vdpa16(mvdev, >>>> VIRTIO_NET_S_LINK_UP); >>>> -    return err; >>>> +    return 0; >>>>    } >>>>    static void mlx5_vdpa_set_config_cb(struct vdpa_device *vdev, >>>> struct vdpa_callback *cb) >