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=ham 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 BC0EDC433E0 for ; Wed, 24 Feb 2021 03:21:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66F5064E6C for ; Wed, 24 Feb 2021 03:21:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233004AbhBXDVn (ORCPT ); Tue, 23 Feb 2021 22:21:43 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36668 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231890AbhBXDVk (ORCPT ); Tue, 23 Feb 2021 22:21:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614136813; 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=4V74H9AMOS6Y0avL8O8KTb4Lqx+oJbogr4tIH2vbj/8=; b=NeW/xperJqsR5RFxTcdTUYT3r9K8djhlZxYV9iinK7QmqZzxt9IoCEYKnZxS1BUQpsWpQ7 5ANMBh7/zB1bbEOZCFt7e46ZlTUzDTz4dBZOpF76K9fyTqNMntl/8PMTv7FYEE/IFPq0b6 aG+3b5kc/AY0cohEtPVgVUcRg/J6JOM= 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-206-5A7vzBEWNR6I5ZX__DNsYg-1; Tue, 23 Feb 2021 22:20:11 -0500 X-MC-Unique: 5A7vzBEWNR6I5ZX__DNsYg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2919B1966321; Wed, 24 Feb 2021 03:20:10 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-193.pek2.redhat.com [10.72.13.193]) by smtp.corp.redhat.com (Postfix) with ESMTP id 460AD62499; Wed, 24 Feb 2021 03:20:02 +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> <20210223082536-mutt-send-email-mst@kernel.org> <3ff5fd23-1db0-2f95-4cf9-711ef403fb62@oracle.com> From: Jason Wang Message-ID: <7e6291a4-30b1-6b59-a2bf-713e7b56826d@redhat.com> Date: Wed, 24 Feb 2021 11:20:01 +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: <3ff5fd23-1db0-2f95-4cf9-711ef403fb62@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 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/2/24 3:35 上午, Si-Wei Liu wrote: > > > On 2/23/2021 5:26 AM, Michael S. Tsirkin wrote: >> On Tue, Feb 23, 2021 at 10:03:57AM +0800, Jason Wang wrote: >>> 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 >> I take it back, reading but not writing seems to be explicitly >> allowed by spec. >> So our way to detect a legacy guest is bogus, need to think what is >> the best way to handle this. > Then maybe revert commit fe36cbe067 and friends, and have QEMU detect > legacy guest? Supposedly only config space write access needs to be > guarded before setting FEATURES_OK. I agree. My understanding is that all vDPA must be modern device (since VIRITO_F_ACCESS_PLATFORM is mandated) instead of transitional device. Thanks > > -Siwie > >>>>> >>>>>>> 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) >