From: Si-Wei Liu <si-wei.liu@oracle.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>
Cc: elic@nvidia.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: Mon, 22 Feb 2021 17:12:12 -0800 [thread overview]
Message-ID: <22fe5923-635b-59f0-7643-2fd5876937c2@oracle.com> (raw)
In-Reply-To: <20210222023040-mutt-send-email-mst@kernel.org>
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
>
>
>>> 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)
next prev parent reply other threads:[~2021-02-23 1:13 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 11:54 [PATCH] vdpa/mlx5: set_features should allow reset to zero 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 [this message]
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
2021-12-11 1:44 ` vdpa legacy guest support (was Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero) Si-Wei Liu
2021-12-12 9:26 ` Michael S. Tsirkin
2021-12-13 3:02 ` Jason Wang
2021-12-13 8:06 ` Michael S. Tsirkin
2021-12-13 8:57 ` Jason Wang
2021-12-13 10:42 ` Michael S. Tsirkin
2021-12-14 1:13 ` Si-Wei Liu
2021-12-14 1:59 ` Si-Wei Liu
2021-12-14 3:01 ` Jason Wang
2021-12-14 5:06 ` Michael S. Tsirkin
2021-12-15 1:05 ` Si-Wei Liu
2021-12-15 2:06 ` Jason Wang
2021-12-15 20:52 ` Si-Wei Liu
2021-12-15 21:33 ` Michael S. Tsirkin
2021-12-16 2:01 ` Si-Wei Liu
2021-12-16 2:53 ` Jason Wang
2021-12-16 22:32 ` Si-Wei Liu
2021-12-17 1:57 ` Jason Wang
2021-12-17 2:00 ` Michael S. Tsirkin
2021-12-17 2:15 ` Jason Wang
2021-12-16 6:35 ` Michael S. Tsirkin
2021-12-16 3:43 ` Jason Wang
2021-12-17 1:08 ` Si-Wei Liu
2021-12-17 2:01 ` Jason Wang
2021-02-22 17:09 ` [PATCH] vdpa/mlx5: set_features should allow reset to zero 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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