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From: Jason Wang <jasowang@redhat.com>
To: Si-Wei Liu <si-wei.liu@oracle.com>, mst@redhat.com, elic@nvidia.com
Cc: linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero
Date: Tue, 23 Feb 2021 10:03:08 +0800
Message-ID: <716ad747-501b-4e95-9785-87161da5940f@redhat.com> (raw)
In-Reply-To: <ee31e93b-5fbb-1999-0e82-983d3e49ad1e@oracle.com>


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 <si-wei.liu@oracle.com>
>>> ---
>>>   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)
>>
>


  reply index

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-19 11:54 Si-Wei Liu
2021-02-21 14:44 ` Eli Cohen
2021-02-21 21:52   ` Michael S. Tsirkin
2021-02-22  6:05     ` Eli Cohen
2021-02-23  9:26       ` Michael S. Tsirkin
2021-02-23  9:48         ` Jason Wang
2021-02-23  9:55           ` Michael S. Tsirkin
2021-02-22  4:14 ` Jason Wang
2021-02-22  7:34   ` Michael S. Tsirkin
2021-02-23  1:12     ` Si-Wei Liu
2021-02-23  2:03       ` Jason Wang
2021-02-23 13:26         ` Michael S. Tsirkin
2021-02-23 19:35           ` Si-Wei Liu
2021-02-24  3:20             ` Jason Wang
2021-02-24  5:17               ` Michael S. Tsirkin
2021-02-24  6:02                 ` Jason Wang
2021-02-24  6:45                 ` Eli Cohen
2021-02-24  6:47                   ` Michael S. Tsirkin
2021-02-24  6:55                     ` Jason Wang
2021-02-24  7:12                       ` Michael S. Tsirkin
2021-02-24 12:40                         ` Eli Cohen
2021-02-24  7:17                       ` Eli Cohen
2021-02-24  5:04             ` Michael S. Tsirkin
2021-02-24  6:04               ` Jason Wang
2021-02-24  6:46                 ` Michael S. Tsirkin
2021-02-24  6:53                   ` Jason Wang
2021-02-24  7:17                     ` Michael S. Tsirkin
     [not found]                       ` <babc654d-8dcd-d8a2-c3b6-d20cc4fc554c@redhat.com>
2021-02-24  8:43                         ` Michael S. Tsirkin
2021-02-24  9:30                           ` Jason Wang
2021-02-28 21:30                             ` Michael S. Tsirkin
2021-03-01  3:53                               ` Jason Wang
2021-02-24 18:24               ` Si-Wei Liu
2021-02-26  0:56                 ` Si-Wei Liu
2021-02-28 21:27                   ` Michael S. Tsirkin
2021-03-01 18:08                     ` Si-Wei Liu
2021-02-28 21:28                 ` Michael S. Tsirkin
2021-02-28 21:34                 ` Michael S. Tsirkin
2021-03-01  3:56                   ` Jason Wang
2021-03-02  9:47                     ` Michael S. Tsirkin
2021-03-02 10:53                       ` Jason Wang
2021-02-22 17:09   ` Si-Wei Liu
2021-02-23  2:03     ` Jason Wang [this message]
2021-02-23  9:25     ` Michael S. Tsirkin
2021-02-23  9:46       ` Jason Wang
2021-02-23 10:01         ` Michael S. Tsirkin
2021-02-23 10:17           ` Jason Wang
2021-02-24  9:40             ` Jason Wang
2021-02-23 10:04         ` [virtio-dev] " Cornelia Huck
2021-02-23 10:31           ` Jason Wang
2021-02-23 10:58             ` Cornelia Huck
2021-02-24  9:29               ` Jason Wang
2021-02-24 11:12                 ` Cornelia Huck
2021-02-25  4:36                   ` Jason Wang
2021-02-25 13:26                     ` Cornelia Huck
2021-02-25 18:53                     ` Michael S. Tsirkin
2021-02-26  8:19                       ` Jason Wang
2021-02-28 21:25                         ` Michael S. Tsirkin
2021-03-01  3:51                           ` Jason Wang
2021-03-02 12:08                             ` Cornelia Huck
     [not found]                               ` <5f6972fe-7246-b622-958d-9cab8dd98e21@redhat.com>
2021-03-03  8:29                                 ` Cornelia Huck
2021-03-04  8:24                                   ` Jason Wang
2021-03-04 13:50                                     ` Cornelia Huck
2021-03-05  3:01                                       ` Jason Wang
2021-02-23 12:26 ` Michael S. Tsirkin

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