ACK/Cmnt: [focal:linux-azure][LP:#1894896][PATCH] hv_netvsc: Fix hibernation for mlx5 VF driver

[Ian May]

LGTM

The first comment of the attached buglink references two additional patches being needed.  Is there a reason those weren't included with this patch?

Thanks
Ian


On 2020-10-27 14:18:22 , Marcelo Henrique Cerri wrote:
> From: Dexuan Cui <decui at microsoft.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1894896
> 
> mlx5_suspend()/resume() keep the network interface, so during hibernation
> netvsc_unregister_vf() and netvsc_register_vf() are not called, and hence
> netvsc_resume() should call netvsc_vf_changed() to switch the data path
> back to the VF after hibernation. Note: after we close and re-open the
> vmbus channel of the netvsc NIC in netvsc_suspend() and netvsc_resume(),
> the data path is implicitly switched to the netvsc NIC. Similarly,
> netvsc_suspend() should not call netvsc_unregister_vf(), otherwise the VF
> can no longer be used after hibernation.
> 
> For mlx4, since the VF network interafce is explicitly destroyed and
> re-created during hibernation (see mlx4_suspend()/resume()), hv_netvsc
> already explicitly switches the data path from and to the VF automatically
> via netvsc_register_vf() and netvsc_unregister_vf(), so mlx4 doesn't need
> this fix. Note: mlx4 can still work with the fix because in
> netvsc_suspend()/resume() ndev_ctx->vf_netdev is NULL for mlx4.
> 
> Fixes: 0efeea5fb153 ("hv_netvsc: Add the support of hibernation")
> Signed-off-by: Dexuan Cui <decui at microsoft.com>
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> (cherry picked from commit 19162fd4063a3211843b997a454b505edb81d5ce)
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
> ---
> 
> Marcelo's comments:
> 
> I was able to reproduce the problem with the current version from
> focal-updates following the test instructions from the LP bug and I
> was also able to confirm the fix solves the problem with a test
> kernel:
> 
> https://kernel.ubuntu.com/~mhcerri/azure/focal-linux-azure_lp1894896.tgz
> 
> 5.8 already received the fix via an upstream stable update
> (LP:#1894896) and hibernation is not supported in 4.15 linux-azure.
> 
> Besides that the fix is a clean cherry-pick from upstream.
> 
> ---
>  drivers/net/hyperv/netvsc_drv.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index 33d9d17ee0e0..be5ede2a6b94 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -2551,8 +2551,8 @@ static int netvsc_remove(struct hv_device *dev)
>  static int netvsc_suspend(struct hv_device *dev)
>  {
>  	struct net_device_context *ndev_ctx;
> -	struct net_device *vf_netdev, *net;
>  	struct netvsc_device *nvdev;
> +	struct net_device *net;
>  	int ret;
>  
>  	net = hv_get_drvdata(dev);
> @@ -2568,10 +2568,6 @@ static int netvsc_suspend(struct hv_device *dev)
>  		goto out;
>  	}
>  
> -	vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
> -	if (vf_netdev)
> -		netvsc_unregister_vf(vf_netdev);
> -
>  	/* Save the current config info */
>  	ndev_ctx->saved_netvsc_dev_info = netvsc_devinfo_get(nvdev);
>  
> @@ -2587,6 +2583,7 @@ static int netvsc_resume(struct hv_device *dev)
>  	struct net_device *net = hv_get_drvdata(dev);
>  	struct net_device_context *net_device_ctx;
>  	struct netvsc_device_info *device_info;
> +	struct net_device *vf_netdev;
>  	int ret;
>  
>  	rtnl_lock();
> @@ -2599,6 +2596,15 @@ static int netvsc_resume(struct hv_device *dev)
>  	netvsc_devinfo_put(device_info);
>  	net_device_ctx->saved_netvsc_dev_info = NULL;
>  
> +	/* A NIC driver (e.g. mlx5) may keep the VF network interface across
> +	 * hibernation, but here the data path is implicitly switched to the
> +	 * netvsc NIC since the vmbus channel is closed and re-opened, so
> +	 * netvsc_vf_changed() must be used to switch the data path to the VF.
> +	 */
> +	vf_netdev = rtnl_dereference(net_device_ctx->vf_netdev);
> +	if (vf_netdev && netvsc_vf_changed(vf_netdev) != NOTIFY_OK)
> +		ret = -EINVAL;
> +
>  	rtnl_unlock();
>  
>  	return ret;
> -- 
> 2.25.1
> 
> 
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