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 2AACBC433E6 for ; Wed, 24 Feb 2021 06:06:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C62F864EC9 for ; Wed, 24 Feb 2021 06:06:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234087AbhBXGGU (ORCPT ); Wed, 24 Feb 2021 01:06:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:22718 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233152AbhBXGGQ (ORCPT ); Wed, 24 Feb 2021 01:06:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614146688; 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=eNYC7vN6C0EshP6R28AJQdQwT0Q3lWhFKQkx/3ebEME=; b=bVEl4gImTHuHrCuGAHyv/3Px9gjq3wShOpOULQt1p0Dl5tuNDigVmsag+TLojfex1bcjYg i6uZbUVdZjOpNA3wqOLvNgBpQnU6emQ/JhIs12TLhZVsS5ksMfqEfcmVN1bMuAtuIsF03h vlJF4ZX6TblnFBgYWW+Izt/kYSda8Fc= 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-62-vgQ0V9W0P026MMgrofv6Cw-1; Wed, 24 Feb 2021 01:04:46 -0500 X-MC-Unique: vgQ0V9W0P026MMgrofv6Cw-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 4D1DE91270; Wed, 24 Feb 2021 06:04:45 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-96.pek2.redhat.com [10.72.13.96]) by smtp.corp.redhat.com (Postfix) with ESMTP id D07046064B; Wed, 24 Feb 2021 06:04:37 +0000 (UTC) Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero To: "Michael S. Tsirkin" , Si-Wei Liu 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> <20210224000057-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <0559fd8c-ff44-cb7a-8a74-71976dd2ee33@redhat.com> Date: Wed, 24 Feb 2021 14:04:36 +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: <20210224000057-mutt-send-email-mst@kernel.org> 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 Archived-At: List-Archive: List-Post: On 2021/2/24 1:04 下午, Michael S. Tsirkin wrote: > On Tue, Feb 23, 2021 at 11:35:57AM -0800, 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. >> >> -Siwie > Detecting it isn't enough though, we will need a new ioctl to notify > the kernel that it's a legacy guest. Ugh :( I'm not sure I get this, how can we know if there's a legacy driver before set_features()? And I wonder what will hapeen if we just revert the set_features(0)? 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)