linux-kernel - RE: [PATCH] hv_netvsc:Register VF in netvsc_probe if NET_DEVICE

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Date: Tue, 30 Jan 2024 22:05:21 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Dexuan Cui <decui@...rosoft.com>, Shradha Gupta
	<shradhagupta@...ux.microsoft.com>, KY Srinivasan <kys@...rosoft.com>, Wei
 Liu <wei.liu@...nel.org>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Wojciech Drewek <wojciech.drewek@...el.com>,
	"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>
CC: Shradha Gupta <shradhagupta@...rosoft.com>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH] hv_netvsc:Register VF in netvsc_probe if
 NET_DEVICE_REGISTER missed



> -----Original Message-----
> From: Dexuan Cui <decui@...rosoft.com>
> Sent: Tuesday, January 30, 2024 3:13 PM
> To: Shradha Gupta <shradhagupta@...ux.microsoft.com>; KY Srinivasan


> 
> > @@ -2205,8 +2209,11 @@ static int netvsc_vf_join(struct net_device
> > *vf_netdev,
> >  			   ndev->name, ret);
> >  		goto upper_link_failed;
> >  	}
> > -
> > -	schedule_delayed_work(&ndev_ctx->vf_takeover,
> > VF_TAKEOVER_INT);
> > +	/* If this registration is called from probe context vf_takeover
> > +	 * is taken care of later in probe itself.
> I suspect "later in probe itself" is not accurate.
> If 'context' is VF_REG_IN_PROBE, I suppose what happens here is:
> after netvsc_probe() finishes, the netvsc interface becomes available,
> so the user space will ifup it, and netvsc_open() will UP the VF
> interface,
> and netvsc_netdev_event() is called for the VF with event ==
> NETDEV_POST_INIT (?) and NETDEV_CHANGE, and the data path is
> switched to the VF.

In register_netdevice(), NETDEV_POST_INIT is earlier than NETDEV_REGISTER.
This case: netvsc_open >> dev_open(vf) >> NETDEV_UP >>
 netvsc_vf_changed(event_dev, event);

> 
> If my understanding is correct, I think in the case of 'context' ==
> VF_REG_IN_PROBE, I suspect the "Align MTU of VF with master"
> and the "sync address list from ndev to VF" in __netvsc_vf_setup() are
> omitted? If so, should this be fixed? e.g. Not sure if the below is an
> issue or not:
> 1) a VF is bound to a NetVSC interface, and a user sets the MTUs to 1024.
> 2) rmmod hv_netvsc
> 3) modprobe hv_netvsc
> 4) the netvsc interface uses MTU=1500 (the default), and the VF still
> uses 1024.

__netvsc_vf_setup() is skipped from the netvsc_register_vf >> netvsc_vf_join(),
but called from netvsc_probe(), so the VF mtu is sync-ed to 1500.
I verified mtu sync in test.

Thanks,
- Haiyang