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 7649EC433E0 for ; Tue, 23 Feb 2021 02:05:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A6EC64E41 for ; Tue, 23 Feb 2021 02:05:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231362AbhBWCEy (ORCPT ); Mon, 22 Feb 2021 21:04:54 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36695 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231237AbhBWCEt (ORCPT ); Mon, 22 Feb 2021 21:04:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614045800; 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=jDvNN3dr07M3oMcu2xiN/23kS7A7X+hTtnNECpm9lbs=; b=A8n2oVCUOjyW3UakAIlRrAAc28VJfjftmd2W1ptgdjdGW0SHDlAzOewj0btdWQcp2xZxnr InH1PfKX8Z0bdqC4OBSr9fL/FWiWV62simoIz7Nl9MS58Z2J8h5wfzUPXLmFHFxoLLo63k xS9HlV0/+DtaTlUayAt8ZcKniEg7tfM= 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-222-rW2wH0N2Nryg4Ia4P5zb2g-1; Mon, 22 Feb 2021 21:03:17 -0500 X-MC-Unique: rW2wH0N2Nryg4Ia4P5zb2g-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 BA3528030BB; Tue, 23 Feb 2021 02:03:15 +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 0962C10016F9; Tue, 23 Feb 2021 02:03:09 +0000 (UTC) Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero To: Si-Wei Liu , mst@redhat.com, elic@nvidia.com Cc: 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> From: Jason Wang Message-ID: <716ad747-501b-4e95-9785-87161da5940f@redhat.com> Date: Tue, 23 Feb 2021 10:03:08 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2021/2/23 1:09 上午, Si-Wei Liu wrote: > > > On 2/21/2021 8:14 PM, 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? > > Isn't the commit 452639a64ad8 itself is a workaround for legacy guest? Yes, but the problem is we can't detect whether or not it's an legacy guest (e.g feature is not set). > > I think the point is, since there's legacy guest we'd have to support, > this host side workaround is unavoidable. Since from vhost-vDPA point of view the driver is Qemu, it means we need make qemu vhost-vDPA driver spec complaint. E.g how about: 1) revert 452639a64ad8 and fix Qemu? In Qemu, during vhost-vDPA initialization, do a minial config sync by neogitating minimal features (e.g just VIRTIO_F_ACCESS_PLATFORM). When FEATURE_OK is not set from guest, we can only allow it to access the config space that is emulated by Qemu? Then > Although I agree the violating driver should be fixed (yes, it's in > today's upstream kernel which exists for a while now). 2) Fix the virtio driver bug. Or a quick workaround is to set (VIRTIO_F_ACCESS_PLATFORM instead of 0) in this case. Thanks > > -Siwei > >> >> 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) >> >