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Si-Wei Liu

2021-Feb-19 11:54 UTC

[PATCH] vdpa/mlx5: set_features should allow reset to zero

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. 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 at 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)
-- 
1.8.3.1

Jason Wang

2021-Feb-22 04:14 UTC

head link

[PATCH] vdpa/mlx5: set_features should allow reset to zero

On 2021/2/19 7:54 ??, 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

> 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 at 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)

Michael S. Tsirkin

2021-Feb-23 12:26 UTC

head link

[PATCH] vdpa/mlx5: set_features should allow reset to zero

On Fri, Feb 19, 2021 at 06:54:58AM -0500, 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. 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")
isn't this more

    vdpa: make sure set_features is invoked for legacy

> Signed-off-by: Si-Wei Liu <si-wei.liu at oracle.com>
I think we at least need to correct the comment in
include/linux/vdpa.h then

Instead of "we assume a legacy guest" we'd say something like
"call set features in case it's a legacy guest".

Generally it's unfortunate. Need to think about what to do here.
Any idea how else we can cleanly detect a legacy guest?
> ---
>  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;
Let's just set VIRTIO_F_ACCESS_PLATFORM in core?
Then we don't need to hack mlx5 ...

> @@ -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)
> -- 
> 1.8.3.1

Virtualization - Feb 2021 - [PATCH] vdpa/mlx5: set_features should allow reset to zero

[PATCH] vdpa/mlx5: set_features should allow reset to zero

[PATCH] vdpa/mlx5: set_features should allow reset to zero

[PATCH] vdpa/mlx5: set_features should allow reset to zero