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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Eli Cohen <elic@nvidia.com>
Cc: Si-Wei Liu <si-wei.liu@oracle.com>,
	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: Wed, 24 Feb 2021 14:55:13 +0800
Message-ID: <ef775724-b5fb-ca70-ed2f-f23d8fbf4cd8@redhat.com> (raw)
In-Reply-To: <20210224014700-mutt-send-email-mst@kernel.org>


On 2021/2/24 2:47 下午, Michael S. Tsirkin wrote:
> On Wed, Feb 24, 2021 at 08:45:20AM +0200, Eli Cohen wrote:
>> On Wed, Feb 24, 2021 at 12:17:58AM -0500, Michael S. Tsirkin wrote:
>>> On Wed, Feb 24, 2021 at 11:20:01AM +0800, Jason Wang wrote:
>>>> 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
>>> Well mlx5 has some code to handle legacy guests ...
>>> Eli, could you comment? Is that support unused right now?
>>>
>> If you mean support for version 1.0, well the knob is there but it's not
>> set in the firmware I use. Note sure if we will support this.
> Hmm you mean it's legacy only right now?
> Well at some point you will want advanced goodies like RSS
> and all that is gated on 1.0 ;)


So if my understanding is correct the device/firmware is legacy but 
require VIRTIO_F_ACCESS_PLATFORM semanic? Looks like a spec violation?

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 <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 [this message]
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
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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