netdev - RE: [PATCH net v2] hv_netvsc: Fix hibernation for mlx5 VF driver

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Date:   Tue, 8 Sep 2020 20:49:14 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net v2] hv_netvsc: Fix hibernation for mlx5 VF driver

From: Dexuan Cui <decui@...rosoft.com>  Sent: Monday, September 7, 2020 12:14 AM
> 
> 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@...rosoft.com>
> ---
> 
> Changes in v2 (Thanks Jakub Kicinski <kuba@...nel.org>):
>     Added coments in the changelog and the code about the implicit
> data path switching to the netvsc when we close/re-open the vmbus
> channels.
>     Used reverse xmas order ordering in netvsc_remove().
> 
>  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 64b0a74c1523..81c5c70b616a 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -2587,8 +2587,8 @@ 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);
> @@ -2604,10 +2604,6 @@ 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);
> 
> @@ -2623,6 +2619,7 @@ 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();
> @@ -2635,6 +2632,15 @@ 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;
> +

I'm a little late looking at this code.  But a question:  Is it possible for
netvsc_resume() to be called before the VF driver's resume function
is called?  If so, is it possible for netvsc_vf_changed() to find that the VF
is not up, and hence to switch the data path away from the VF instead of
to the VF?

Michael

>  	rtnl_unlock();
> 
>  	return ret;
> --
> 2.19.1