[PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Jarod Wilson]

hyperv_net:
- set min/max_mtu

virtio_net:
- set min/max_mtu
- remove virtnet_change_mtu

vmxnet3:
- set min/max_mtu

CC: netdev@vger.kernel.org
CC: virtualization@lists.linux-foundation.org
CC: "K. Y. Srinivasan" <kys@microsoft.com>
CC: Haiyang Zhang <haiyangz@microsoft.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Shrikrishna Khare <skhare@vmware.com>
CC: "VMware, Inc." <pv-drivers@vmware.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
---
 drivers/net/hyperv/hyperv_net.h   |  4 ++--
 drivers/net/hyperv/netvsc_drv.c   | 14 +++++++-------
 drivers/net/virtio_net.c          | 23 ++++++++++-------------
 drivers/net/vmxnet3/vmxnet3_drv.c |  7 ++++---
 4 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index f4fbcb5..3958ada 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -606,8 +606,8 @@ struct nvsp_message {
 } __packed;
 
 
-#define NETVSC_MTU 65536
-#define NETVSC_MTU_MIN 68
+#define NETVSC_MTU 65535
+#define NETVSC_MTU_MIN ETH_MIN_MTU
 
 #define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
 #define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f0919bd..3dc9679 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -872,19 +872,12 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	struct netvsc_device *nvdev = ndevctx->nvdev;
 	struct hv_device *hdev = ndevctx->device_ctx;
 	struct netvsc_device_info device_info;
-	int limit = ETH_DATA_LEN;
 	u32 num_chn;
 	int ret = 0;
 
 	if (ndevctx->start_remove || !nvdev || nvdev->destroy)
 		return -ENODEV;
 
-	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
-		limit = NETVSC_MTU - ETH_HLEN;
-
-	if (mtu < NETVSC_MTU_MIN || mtu > limit)
-		return -EINVAL;
-
 	ret = netvsc_close(ndev);
 	if (ret)
 		goto out;
@@ -1343,6 +1336,13 @@ static int netvsc_probe(struct hv_device *dev,
 
 	netif_carrier_off(net);
 
+	/* MTU range: 68 - 1500 or 65521 */
+	net->min_mtu = NETVSC_MTU_MIN;
+	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
+		net->max_mtu = NETVSC_MTU - ETH_HLEN;
+	else
+		net->max_mtu = ETH_DATA_LEN;
+
 	netvsc_init_settings(net);
 
 	net_device_ctx = netdev_priv(net);
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fad84f3..4885a42 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
 	.set_settings = virtnet_set_settings,
 };
 
-#define MIN_MTU 68
-#define MAX_MTU 65535
-
-static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
-{
-	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
-		return -EINVAL;
-	dev->mtu = new_mtu;
-	return 0;
-}
-
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_validate_addr   = eth_validate_addr,
 	.ndo_set_mac_address = virtnet_set_mac_address,
 	.ndo_set_rx_mode     = virtnet_set_rx_mode,
-	.ndo_change_mtu	     = virtnet_change_mtu,
 	.ndo_get_stats64     = virtnet_stats,
 	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
 	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
@@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
 	return true;
 }
 
+#define MIN_MTU ETH_MIN_MTU
+#define MAX_MTU 65535
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err;
@@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	dev->vlan_features = dev->features;
 
+	/* MTU range: 68 - 65535 */
+	dev->min_mtu = MIN_MTU;
+	dev->max_mtu = MAX_MTU;
+
 	/* Configuration may specify what MAC to use.  Otherwise random. */
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
 		virtio_cread_bytes(vdev,
@@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 		mtu = virtio_cread16(vdev,
 				     offsetof(struct virtio_net_config,
 					      mtu));
-		if (virtnet_change_mtu(dev, mtu))
+		if (mtu >= dev->min_mtu && mtu <= dev->max_mtu) {
+			dev->mtu = mtu;
 			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
+		}
 	}
 
 	if (vi->any_header_sg)
diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
index b5554f2..0c36de1 100644
--- a/drivers/net/vmxnet3/vmxnet3_drv.c
+++ b/drivers/net/vmxnet3/vmxnet3_drv.c
@@ -2969,9 +2969,6 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
 	struct vmxnet3_adapter *adapter = netdev_priv(netdev);
 	int err = 0;
 
-	if (new_mtu < VMXNET3_MIN_MTU || new_mtu > VMXNET3_MAX_MTU)
-		return -EINVAL;
-
 	netdev->mtu = new_mtu;
 
 	/*
@@ -3428,6 +3425,10 @@ vmxnet3_probe_device(struct pci_dev *pdev,
 	vmxnet3_set_ethtool_ops(netdev);
 	netdev->watchdog_timeo = 5 * HZ;
 
+	/* MTU range: 60 - 9000 */
+	netdev->min_mtu = VMXNET3_MIN_MTU;
+	netdev->max_mtu = VMXNET3_MAX_MTU;
+
 	INIT_WORK(&adapter->work, vmxnet3_reset_work);
 	set_bit(VMXNET3_STATE_BIT_QUIESCED, &adapter->state);
 
-- 
2.10.0

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Aaron Conole]

Jarod Wilson <jarod@redhat.com> writes:

> hyperv_net:
> - set min/max_mtu
>
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
>
> vmxnet3:
> - set min/max_mtu
>
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>
> ---


The virtnet change looks good to me.  It simplifies an enhancement that
I was about to propose, so I'll let yours land first.

-Aaron

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Michael S. Tsirkin]

On Tue, Oct 18, 2016 at 10:33:32PM -0400, Jarod Wilson wrote:
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fad84f3..4885a42 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.set_settings = virtnet_set_settings,
>  };
>  
> -#define MIN_MTU 68
> -#define MAX_MTU 65535
> -
> -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> -{
> -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> -		return -EINVAL;
> -	dev->mtu = new_mtu;
> -	return 0;
> -}
> -
>  static const struct net_device_ops virtnet_netdev = {
>  	.ndo_open            = virtnet_open,
>  	.ndo_stop   	     = virtnet_close,
> @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
>  	.ndo_validate_addr   = eth_validate_addr,
>  	.ndo_set_mac_address = virtnet_set_mac_address,
>  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> -	.ndo_change_mtu	     = virtnet_change_mtu,
>  	.ndo_get_stats64     = virtnet_stats,
>  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
>  	return true;
>  }
>  
> +#define MIN_MTU ETH_MIN_MTU
> +#define MAX_MTU 65535
> +

Do we need a common macro for this?

>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;
> @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  
>  	dev->vlan_features = dev->features;
>  
> +	/* MTU range: 68 - 65535 */
> +	dev->min_mtu = MIN_MTU;
> +	dev->max_mtu = MAX_MTU;
> +
>  	/* Configuration may specify what MAC to use.  Otherwise random. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
>  		virtio_cread_bytes(vdev,
> @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		mtu = virtio_cread16(vdev,
>  				     offsetof(struct virtio_net_config,
>  					      mtu));
> -		if (virtnet_change_mtu(dev, mtu))
> +		if (mtu >= dev->min_mtu && mtu <= dev->max_mtu) {
> +			dev->mtu = mtu;
>  			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);

I think the logic is wrong here:

If mtu is legal, we set it but do not tell host.
If it's out of range we tell host we use it
but don't actually.

Should be the reverse.

> +		}
>  	}
>  
>  	if (vi->any_header_sg)

-- 
MST

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Michael S. Tsirkin]

On Wed, Oct 19, 2016 at 04:59:46PM +0300, Michael S. Tsirkin wrote:
> On Tue, Oct 18, 2016 at 10:33:32PM -0400, Jarod Wilson wrote:
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index fad84f3..4885a42 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> >  	.set_settings = virtnet_set_settings,
> >  };
> >  
> > -#define MIN_MTU 68
> > -#define MAX_MTU 65535
> > -
> > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > -{
> > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > -		return -EINVAL;
> > -	dev->mtu = new_mtu;
> > -	return 0;
> > -}
> > -
> >  static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_open            = virtnet_open,
> >  	.ndo_stop   	     = virtnet_close,
> > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_validate_addr   = eth_validate_addr,
> >  	.ndo_set_mac_address = virtnet_set_mac_address,
> >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > -	.ndo_change_mtu	     = virtnet_change_mtu,
> >  	.ndo_get_stats64     = virtnet_stats,
> >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
> >  	return true;
> >  }
> >  
> > +#define MIN_MTU ETH_MIN_MTU
> > +#define MAX_MTU 65535
> > +
> 
> Do we need a common macro for this?

I think it's actually IP_MAX_MTU.

> >  static int virtnet_probe(struct virtio_device *vdev)
> >  {
> >  	int i, err;
> > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  
> >  	dev->vlan_features = dev->features;
> >  
> > +	/* MTU range: 68 - 65535 */
> > +	dev->min_mtu = MIN_MTU;
> > +	dev->max_mtu = MAX_MTU;
> > +
> >  	/* Configuration may specify what MAC to use.  Otherwise random. */
> >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> >  		virtio_cread_bytes(vdev,
> > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  		mtu = virtio_cread16(vdev,
> >  				     offsetof(struct virtio_net_config,
> >  					      mtu));
> > -		if (virtnet_change_mtu(dev, mtu))
> > +		if (mtu >= dev->min_mtu && mtu <= dev->max_mtu) {
> > +			dev->mtu = mtu;
> >  			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
> 
> I think the logic is wrong here:
> 
> If mtu is legal, we set it but do not tell host.
> If it's out of range we tell host we use it
> but don't actually.
> 
> Should be the reverse.
> 
> > +		}
> >  	}
> >  
> >  	if (vi->any_header_sg)
> 
> -- 
> MST

RE: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Haiyang Zhang via Virtualization]

> -----Original Message-----
> From: Jarod Wilson [mailto:jarod@redhat.com]
> Sent: Tuesday, October 18, 2016 10:34 PM
> To: linux-kernel@vger.kernel.org
> Cc: Jarod Wilson <jarod@redhat.com>; netdev@vger.kernel.org;
> virtualization@lists.linux-foundation.org; KY Srinivasan
> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Michael S.
> Tsirkin <mst@redhat.com>; Shrikrishna Khare <skhare@vmware.com>; VMware,
> Inc. <pv-drivers@vmware.com>
> Subject: [PATCH net-next 5/6] net: use core MTU range checking in virt
> drivers
> 
> hyperv_net:
> - set min/max_mtu
> 
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
> 
> vmxnet3:
> - set min/max_mtu
> 
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>
> ---
>  drivers/net/hyperv/hyperv_net.h   |  4 ++--
>  drivers/net/hyperv/netvsc_drv.c   | 14 +++++++-------
>  drivers/net/virtio_net.c          | 23 ++++++++++-------------
>  drivers/net/vmxnet3/vmxnet3_drv.c |  7 ++++---
>  4 files changed, 23 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/net/hyperv/hyperv_net.h
> b/drivers/net/hyperv/hyperv_net.h
> index f4fbcb5..3958ada 100644
> --- a/drivers/net/hyperv/hyperv_net.h
> +++ b/drivers/net/hyperv/hyperv_net.h
> @@ -606,8 +606,8 @@ struct nvsp_message {
>  } __packed;
> 
> 
> -#define NETVSC_MTU 65536
> -#define NETVSC_MTU_MIN 68
> +#define NETVSC_MTU 65535

Why change it to 65535? For Hyperv host, this should be 65536.


> @@ -1343,6 +1336,13 @@ static int netvsc_probe(struct hv_device *dev,
> 
>  	netif_carrier_off(net);
> 
> +	/* MTU range: 68 - 1500 or 65521 */
> +	net->min_mtu = NETVSC_MTU_MIN;
> +	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
> +		net->max_mtu = NETVSC_MTU - ETH_HLEN;
> +	else
> +		net->max_mtu = ETH_DATA_LEN;
> +
>  	netvsc_init_settings(net);
> 
>  	net_device_ctx = netdev_priv(net);

nvdev->nvsp_version is not set until after rndis_filter_device_add()
is successfully completed.
You need to move this part to the place just before this line:
 ret = register_netdev(net);

Thanks,
- Haiyang

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Jarod Wilson]

On Wed, Oct 19, 2016 at 04:59:46PM +0300, Michael S. Tsirkin wrote:
> On Tue, Oct 18, 2016 at 10:33:32PM -0400, Jarod Wilson wrote:
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index fad84f3..4885a42 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> >  	.set_settings = virtnet_set_settings,
> >  };
> >  
> > -#define MIN_MTU 68
> > -#define MAX_MTU 65535
> > -
> > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > -{
> > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > -		return -EINVAL;
> > -	dev->mtu = new_mtu;
> > -	return 0;
> > -}
> > -
> >  static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_open            = virtnet_open,
> >  	.ndo_stop   	     = virtnet_close,
> > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_validate_addr   = eth_validate_addr,
> >  	.ndo_set_mac_address = virtnet_set_mac_address,
> >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > -	.ndo_change_mtu	     = virtnet_change_mtu,
> >  	.ndo_get_stats64     = virtnet_stats,
> >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
> >  	return true;
> >  }
> >  
> > +#define MIN_MTU ETH_MIN_MTU
> > +#define MAX_MTU 65535
> > +
> 
> Do we need a common macro for this?

Probably. That value crops up in multiple drivers.

> >  static int virtnet_probe(struct virtio_device *vdev)
> >  {
> >  	int i, err;
> > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  
> >  	dev->vlan_features = dev->features;
> >  
> > +	/* MTU range: 68 - 65535 */
> > +	dev->min_mtu = MIN_MTU;
> > +	dev->max_mtu = MAX_MTU;
> > +
> >  	/* Configuration may specify what MAC to use.  Otherwise random. */
> >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> >  		virtio_cread_bytes(vdev,
> > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  		mtu = virtio_cread16(vdev,
> >  				     offsetof(struct virtio_net_config,
> >  					      mtu));
> > -		if (virtnet_change_mtu(dev, mtu))
> > +		if (mtu >= dev->min_mtu && mtu <= dev->max_mtu) {
> > +			dev->mtu = mtu;
> >  			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
> 
> I think the logic is wrong here:
> 
> If mtu is legal, we set it but do not tell host.
> If it's out of range we tell host we use it
> but don't actually.
> 
> Should be the reverse.

Ah, yes, looks like it should be:

                if (mtu < dev->min_mtu || mtu > dev->max_mtu)
                        __virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
                else
                        dev->mtu = mtu;

-- 
Jarod Wilson
jarod@redhat.com

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Jarod Wilson]

On Wed, Oct 19, 2016 at 05:03:43PM +0300, Michael S. Tsirkin wrote:
> On Wed, Oct 19, 2016 at 04:59:46PM +0300, Michael S. Tsirkin wrote:
> > On Tue, Oct 18, 2016 at 10:33:32PM -0400, Jarod Wilson wrote:
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index fad84f3..4885a42 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> > >  	.set_settings = virtnet_set_settings,
> > >  };
> > >  
> > > -#define MIN_MTU 68
> > > -#define MAX_MTU 65535
> > > -
> > > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > > -{
> > > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > > -		return -EINVAL;
> > > -	dev->mtu = new_mtu;
> > > -	return 0;
> > > -}
> > > -
> > >  static const struct net_device_ops virtnet_netdev = {
> > >  	.ndo_open            = virtnet_open,
> > >  	.ndo_stop   	     = virtnet_close,
> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
> > >  	.ndo_validate_addr   = eth_validate_addr,
> > >  	.ndo_set_mac_address = virtnet_set_mac_address,
> > >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > > -	.ndo_change_mtu	     = virtnet_change_mtu,
> > >  	.ndo_get_stats64     = virtnet_stats,
> > >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> > >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
> > >  	return true;
> > >  }
> > >  
> > > +#define MIN_MTU ETH_MIN_MTU
> > > +#define MAX_MTU 65535
> > > +
> > 
> > Do we need a common macro for this?
> 
> I think it's actually IP_MAX_MTU.

Ah, yes, it is. I'm not sure why I didn't use that...

-- 
Jarod Wilson
jarod@redhat.com

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Jarod Wilson]

On Wed, Oct 19, 2016 at 02:07:47PM +0000, Haiyang Zhang wrote:
> 
> 
> > -----Original Message-----
> > From: Jarod Wilson [mailto:jarod@redhat.com]
> > Sent: Tuesday, October 18, 2016 10:34 PM
> > To: linux-kernel@vger.kernel.org
> > Cc: Jarod Wilson <jarod@redhat.com>; netdev@vger.kernel.org;
> > virtualization@lists.linux-foundation.org; KY Srinivasan
> > <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Michael S.
> > Tsirkin <mst@redhat.com>; Shrikrishna Khare <skhare@vmware.com>; VMware,
> > Inc. <pv-drivers@vmware.com>
> > Subject: [PATCH net-next 5/6] net: use core MTU range checking in virt
> > drivers
> > 
> > hyperv_net:
> > - set min/max_mtu
> > 
> > virtio_net:
> > - set min/max_mtu
> > - remove virtnet_change_mtu
> > 
> > vmxnet3:
> > - set min/max_mtu
> > 
> > CC: netdev@vger.kernel.org
> > CC: virtualization@lists.linux-foundation.org
> > CC: "K. Y. Srinivasan" <kys@microsoft.com>
> > CC: Haiyang Zhang <haiyangz@microsoft.com>
> > CC: "Michael S. Tsirkin" <mst@redhat.com>
> > CC: Shrikrishna Khare <skhare@vmware.com>
> > CC: "VMware, Inc." <pv-drivers@vmware.com>
> > Signed-off-by: Jarod Wilson <jarod@redhat.com>
> > ---
> >  drivers/net/hyperv/hyperv_net.h   |  4 ++--
> >  drivers/net/hyperv/netvsc_drv.c   | 14 +++++++-------
> >  drivers/net/virtio_net.c          | 23 ++++++++++-------------
> >  drivers/net/vmxnet3/vmxnet3_drv.c |  7 ++++---
> >  4 files changed, 23 insertions(+), 25 deletions(-)
> > 
> > diff --git a/drivers/net/hyperv/hyperv_net.h
> > b/drivers/net/hyperv/hyperv_net.h
> > index f4fbcb5..3958ada 100644
> > --- a/drivers/net/hyperv/hyperv_net.h
> > +++ b/drivers/net/hyperv/hyperv_net.h
> > @@ -606,8 +606,8 @@ struct nvsp_message {
> >  } __packed;
> > 
> > 
> > -#define NETVSC_MTU 65536
> > -#define NETVSC_MTU_MIN 68
> > +#define NETVSC_MTU 65535
> 
> Why change it to 65535? For Hyperv host, this should be 65536.

Forgot to call this change out, sorry. That was changed, because of
IP_MAX_MTU being 0xFFFFU -> 65535.

> > @@ -1343,6 +1336,13 @@ static int netvsc_probe(struct hv_device *dev,
> > 
> >  	netif_carrier_off(net);
> > 
> > +	/* MTU range: 68 - 1500 or 65521 */
> > +	net->min_mtu = NETVSC_MTU_MIN;
> > +	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
> > +		net->max_mtu = NETVSC_MTU - ETH_HLEN;
> > +	else
> > +		net->max_mtu = ETH_DATA_LEN;
> > +
> >  	netvsc_init_settings(net);
> > 
> >  	net_device_ctx = netdev_priv(net);
> 
> nvdev->nvsp_version is not set until after rndis_filter_device_add()
> is successfully completed.
> You need to move this part to the place just before this line:
>  ret = register_netdev(net);

Okay, will fix that up.

-- 
Jarod Wilson
jarod@redhat.com

Re: [PATCH net-next 5/6] net: use core MTU range checking in virt drivers

[Shrikrishna Khare]

On Wed, 19 Oct 2016, Jarod Wilson wrote:

> hyperv_net:
> - set min/max_mtu
> 
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
> 
> vmxnet3:
> - set min/max_mtu
> 
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>
> ---

The vmxnet3 part of the change looks good to me.

Thanks,
Shri

[PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Jarod Wilson]

hyperv_net:
- set min/max_mtu, per Haiyang, after rndis_filter_device_add

virtio_net:
- set min/max_mtu
- remove virtnet_change_mtu

vmxnet3:
- set min/max_mtu

xen-netback:
- min_mtu = 0, max_mtu = 65517

xen-netfront:
- min_mtu = 0, max_mtu = 65535

unisys/visor:
- clean up defines a little to not clash with network core or add
  redundat definitions

CC: netdev@vger.kernel.org
CC: virtualization@lists.linux-foundation.org
CC: "K. Y. Srinivasan" <kys@microsoft.com>
CC: Haiyang Zhang <haiyangz@microsoft.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Shrikrishna Khare <skhare@vmware.com>
CC: "VMware, Inc." <pv-drivers@vmware.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Paul Durrant <paul.durrant@citrix.com>
CC: David Kershner <david.kershner@unisys.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
---
 drivers/net/hyperv/hyperv_net.h                 |  4 ++--
 drivers/net/hyperv/netvsc_drv.c                 | 14 +++++++-------
 drivers/net/virtio_net.c                        | 23 ++++++++++-------------
 drivers/net/vmxnet3/vmxnet3_drv.c               |  7 ++++---
 drivers/net/xen-netback/interface.c             |  5 ++++-
 drivers/net/xen-netfront.c                      |  2 ++
 drivers/staging/unisys/include/iochannel.h      | 10 ++++------
 drivers/staging/unisys/visornic/visornic_main.c |  4 ++--
 8 files changed, 35 insertions(+), 34 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index f4fbcb5..3958ada 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -606,8 +606,8 @@ struct nvsp_message {
 } __packed;
 
 
-#define NETVSC_MTU 65536
-#define NETVSC_MTU_MIN 68
+#define NETVSC_MTU 65535
+#define NETVSC_MTU_MIN ETH_MIN_MTU
 
 #define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
 #define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f0919bd..3b28cf1 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -872,19 +872,12 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
 	struct netvsc_device *nvdev = ndevctx->nvdev;
 	struct hv_device *hdev = ndevctx->device_ctx;
 	struct netvsc_device_info device_info;
-	int limit = ETH_DATA_LEN;
 	u32 num_chn;
 	int ret = 0;
 
 	if (ndevctx->start_remove || !nvdev || nvdev->destroy)
 		return -ENODEV;
 
-	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
-		limit = NETVSC_MTU - ETH_HLEN;
-
-	if (mtu < NETVSC_MTU_MIN || mtu > limit)
-		return -EINVAL;
-
 	ret = netvsc_close(ndev);
 	if (ret)
 		goto out;
@@ -1402,6 +1395,13 @@ static int netvsc_probe(struct hv_device *dev,
 	netif_set_real_num_tx_queues(net, nvdev->num_chn);
 	netif_set_real_num_rx_queues(net, nvdev->num_chn);
 
+	/* MTU range: 68 - 1500 or 65521 */
+	net->min_mtu = NETVSC_MTU_MIN;
+	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
+		net->max_mtu = NETVSC_MTU - ETH_HLEN;
+	else
+		net->max_mtu = ETH_DATA_LEN;
+
 	ret = register_netdev(net);
 	if (ret != 0) {
 		pr_err("Unable to register netdev.\n");
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fad84f3..720809f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
 	.set_settings = virtnet_set_settings,
 };
 
-#define MIN_MTU 68
-#define MAX_MTU 65535
-
-static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
-{
-	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
-		return -EINVAL;
-	dev->mtu = new_mtu;
-	return 0;
-}
-
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_validate_addr   = eth_validate_addr,
 	.ndo_set_mac_address = virtnet_set_mac_address,
 	.ndo_set_rx_mode     = virtnet_set_rx_mode,
-	.ndo_change_mtu	     = virtnet_change_mtu,
 	.ndo_get_stats64     = virtnet_stats,
 	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
 	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
@@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
 	return true;
 }
 
+#define MIN_MTU ETH_MIN_MTU
+#define MAX_MTU ETH_MAX_MTU
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err;
@@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	dev->vlan_features = dev->features;
 
+	/* MTU range: 68 - 65535 */
+	dev->min_mtu = MIN_MTU;
+	dev->max_mtu = MAX_MTU;
+
 	/* Configuration may specify what MAC to use.  Otherwise random. */
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
 		virtio_cread_bytes(vdev,
@@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
 		mtu = virtio_cread16(vdev,
 				     offsetof(struct virtio_net_config,
 					      mtu));
-		if (virtnet_change_mtu(dev, mtu))
+		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
 			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
+		else
+			dev->mtu = mtu;
 	}
 
 	if (vi->any_header_sg)
diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
index b5554f2..0c36de1 100644
--- a/drivers/net/vmxnet3/vmxnet3_drv.c
+++ b/drivers/net/vmxnet3/vmxnet3_drv.c
@@ -2969,9 +2969,6 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
 	struct vmxnet3_adapter *adapter = netdev_priv(netdev);
 	int err = 0;
 
-	if (new_mtu < VMXNET3_MIN_MTU || new_mtu > VMXNET3_MAX_MTU)
-		return -EINVAL;
-
 	netdev->mtu = new_mtu;
 
 	/*
@@ -3428,6 +3425,10 @@ vmxnet3_probe_device(struct pci_dev *pdev,
 	vmxnet3_set_ethtool_ops(netdev);
 	netdev->watchdog_timeo = 5 * HZ;
 
+	/* MTU range: 60 - 9000 */
+	netdev->min_mtu = VMXNET3_MIN_MTU;
+	netdev->max_mtu = VMXNET3_MAX_MTU;
+
 	INIT_WORK(&adapter->work, vmxnet3_reset_work);
 	set_bit(VMXNET3_STATE_BIT_QUIESCED, &adapter->state);
 
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 74dc2bf..e30ffd2 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -302,7 +302,7 @@ static int xenvif_close(struct net_device *dev)
 static int xenvif_change_mtu(struct net_device *dev, int mtu)
 {
 	struct xenvif *vif = netdev_priv(dev);
-	int max = vif->can_sg ? 65535 - VLAN_ETH_HLEN : ETH_DATA_LEN;
+	int max = vif->can_sg ? ETH_MAX_MTU - VLAN_ETH_HLEN : ETH_DATA_LEN;
 
 	if (mtu > max)
 		return -EINVAL;
@@ -471,6 +471,9 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 
 	dev->tx_queue_len = XENVIF_QUEUE_LENGTH;
 
+	dev->min_mtu = 0;
+	dev->max_mtu = ETH_MAX_MTU - VLAN_ETH_HLEN;
+
 	/*
 	 * Initialise a dummy MAC address. We choose the numerically
 	 * largest non-broadcast address to prevent the address getting
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index e17879d..7d616b0 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1329,6 +1329,8 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
 	netdev->features |= netdev->hw_features;
 
 	netdev->ethtool_ops = &xennet_ethtool_ops;
+	netdev->min_mtu = 0;
+	netdev->max_mtu = XEN_NETIF_MAX_TX_SIZE;
 	SET_NETDEV_DEV(netdev, &dev->dev);
 
 	np->netdev = netdev;
diff --git a/drivers/staging/unisys/include/iochannel.h b/drivers/staging/unisys/include/iochannel.h
index cba4433..9081b3f 100644
--- a/drivers/staging/unisys/include/iochannel.h
+++ b/drivers/staging/unisys/include/iochannel.h
@@ -113,12 +113,10 @@ enum net_types {
 
 };
 
-#define		ETH_HEADER_SIZE 14	/* size of ethernet header */
-
 #define		ETH_MIN_DATA_SIZE 46	/* minimum eth data size */
-#define		ETH_MIN_PACKET_SIZE (ETH_HEADER_SIZE + ETH_MIN_DATA_SIZE)
+#define		ETH_MIN_PACKET_SIZE (ETH_HLEN + ETH_MIN_DATA_SIZE)
 
-#define		ETH_MAX_MTU 16384	/* maximum data size */
+#define		VISOR_ETH_MAX_MTU 16384	/* maximum data size */
 
 #ifndef MAX_MACADDR_LEN
 #define MAX_MACADDR_LEN 6	/* number of bytes in MAC address */
@@ -288,7 +286,7 @@ struct net_pkt_xmt {
 	int len;	/* full length of data in the packet */
 	int num_frags;	/* number of fragments in frags containing data */
 	struct phys_info frags[MAX_PHYS_INFO];	/* physical page information */
-	char ethhdr[ETH_HEADER_SIZE];	/* the ethernet header  */
+	char ethhdr[ETH_HLEN];	/* the ethernet header  */
 	struct {
 		/* these are needed for csum at uisnic end */
 		u8 valid;	/* 1 = struct is valid - else ignore */
@@ -323,7 +321,7 @@ struct net_pkt_xmtdone {
  */
 #define RCVPOST_BUF_SIZE 4032
 #define MAX_NET_RCV_CHAIN \
-	((ETH_MAX_MTU + ETH_HEADER_SIZE + RCVPOST_BUF_SIZE - 1) \
+	((VISOR_ETH_MAX_MTU + ETH_HLEN + RCVPOST_BUF_SIZE - 1) \
 	/ RCVPOST_BUF_SIZE)
 
 struct net_pkt_rcvpost {
diff --git a/drivers/staging/unisys/visornic/visornic_main.c b/drivers/staging/unisys/visornic/visornic_main.c
index 1367007..f8a584b 100644
--- a/drivers/staging/unisys/visornic/visornic_main.c
+++ b/drivers/staging/unisys/visornic/visornic_main.c
@@ -791,7 +791,7 @@ visornic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	 * pointing to
 	 */
 	firstfraglen = skb->len - skb->data_len;
-	if (firstfraglen < ETH_HEADER_SIZE) {
+	if (firstfraglen < ETH_HLEN) {
 		spin_unlock_irqrestore(&devdata->priv_lock, flags);
 		devdata->busy_cnt++;
 		dev_err(&netdev->dev,
@@ -864,7 +864,7 @@ visornic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	/* copy ethernet header from first frag into ocmdrsp
 	 * - everything else will be pass in frags & DMA'ed
 	 */
-	memcpy(cmdrsp->net.xmt.ethhdr, skb->data, ETH_HEADER_SIZE);
+	memcpy(cmdrsp->net.xmt.ethhdr, skb->data, ETH_HLEN);
 	/* copy frags info - from skb->data we need to only provide access
 	 * beyond eth header
 	 */
-- 
2.10.0

RE: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Haiyang Zhang via Virtualization]

> -----Original Message-----
> From: Jarod Wilson [mailto:jarod@redhat.com]
> Sent: Thursday, October 20, 2016 1:55 PM
> To: linux-kernel@vger.kernel.org
> Cc: Jarod Wilson <jarod@redhat.com>; netdev@vger.kernel.org;
> virtualization@lists.linux-foundation.org; KY Srinivasan
> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Michael S.
> Tsirkin <mst@redhat.com>; Shrikrishna Khare <skhare@vmware.com>; VMware,
> Inc. <pv-drivers@vmware.com>; Wei Liu <wei.liu2@citrix.com>; Paul
> Durrant <paul.durrant@citrix.com>; David Kershner
> <david.kershner@unisys.com>
> Subject: [PATCH net-next v2 6/9] net: use core MTU range checking in
> virt drivers
> 
> hyperv_net:
> - set min/max_mtu, per Haiyang, after rndis_filter_device_add
> 
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
> 
> vmxnet3:
> - set min/max_mtu
> 
> xen-netback:
> - min_mtu = 0, max_mtu = 65517
> 
> xen-netfront:
> - min_mtu = 0, max_mtu = 65535
> 
> unisys/visor:
> - clean up defines a little to not clash with network core or add
>   redundat definitions
> 
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Paul Durrant <paul.durrant@citrix.com>
> CC: David Kershner <david.kershner@unisys.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>
> ---

The hv_netvsc changes look fine. Thanks.

Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>

Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Michael S. Tsirkin]

On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
> hyperv_net:
> - set min/max_mtu, per Haiyang, after rndis_filter_device_add
> 
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
> vmxnet3:
> - set min/max_mtu
> 
> xen-netback:
> - min_mtu = 0, max_mtu = 65517
> 
> xen-netfront:
> - min_mtu = 0, max_mtu = 65535
> 
> unisys/visor:
> - clean up defines a little to not clash with network core or add
>   redundat definitions
> 
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Paul Durrant <paul.durrant@citrix.com>
> CC: David Kershner <david.kershner@unisys.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>
> ---
>  drivers/net/hyperv/hyperv_net.h                 |  4 ++--
>  drivers/net/hyperv/netvsc_drv.c                 | 14 +++++++-------
>  drivers/net/virtio_net.c                        | 23 ++++++++++-------------
>  drivers/net/vmxnet3/vmxnet3_drv.c               |  7 ++++---
>  drivers/net/xen-netback/interface.c             |  5 ++++-
>  drivers/net/xen-netfront.c                      |  2 ++
>  drivers/staging/unisys/include/iochannel.h      | 10 ++++------
>  drivers/staging/unisys/visornic/visornic_main.c |  4 ++--
>  8 files changed, 35 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
> index f4fbcb5..3958ada 100644
> --- a/drivers/net/hyperv/hyperv_net.h
> +++ b/drivers/net/hyperv/hyperv_net.h
> @@ -606,8 +606,8 @@ struct nvsp_message {
>  } __packed;
>  
>  
> -#define NETVSC_MTU 65536
> -#define NETVSC_MTU_MIN 68
> +#define NETVSC_MTU 65535
> +#define NETVSC_MTU_MIN ETH_MIN_MTU
>  
>  #define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
>  #define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
> diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
> index f0919bd..3b28cf1 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -872,19 +872,12 @@ static int netvsc_change_mtu(struct net_device *ndev, int mtu)
>  	struct netvsc_device *nvdev = ndevctx->nvdev;
>  	struct hv_device *hdev = ndevctx->device_ctx;
>  	struct netvsc_device_info device_info;
> -	int limit = ETH_DATA_LEN;
>  	u32 num_chn;
>  	int ret = 0;
>  
>  	if (ndevctx->start_remove || !nvdev || nvdev->destroy)
>  		return -ENODEV;
>  
> -	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
> -		limit = NETVSC_MTU - ETH_HLEN;
> -
> -	if (mtu < NETVSC_MTU_MIN || mtu > limit)
> -		return -EINVAL;
> -
>  	ret = netvsc_close(ndev);
>  	if (ret)
>  		goto out;
> @@ -1402,6 +1395,13 @@ static int netvsc_probe(struct hv_device *dev,
>  	netif_set_real_num_tx_queues(net, nvdev->num_chn);
>  	netif_set_real_num_rx_queues(net, nvdev->num_chn);
>  
> +	/* MTU range: 68 - 1500 or 65521 */
> +	net->min_mtu = NETVSC_MTU_MIN;
> +	if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
> +		net->max_mtu = NETVSC_MTU - ETH_HLEN;
> +	else
> +		net->max_mtu = ETH_DATA_LEN;
> +
>  	ret = register_netdev(net);
>  	if (ret != 0) {
>  		pr_err("Unable to register netdev.\n");
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fad84f3..720809f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.set_settings = virtnet_set_settings,
>  };
>  
> -#define MIN_MTU 68
> -#define MAX_MTU 65535
> -
> -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> -{
> -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> -		return -EINVAL;
> -	dev->mtu = new_mtu;
> -	return 0;
> -}
> -
>  static const struct net_device_ops virtnet_netdev = {
>  	.ndo_open            = virtnet_open,
>  	.ndo_stop   	     = virtnet_close,
> @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
>  	.ndo_validate_addr   = eth_validate_addr,
>  	.ndo_set_mac_address = virtnet_set_mac_address,
>  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> -	.ndo_change_mtu	     = virtnet_change_mtu,
>  	.ndo_get_stats64     = virtnet_stats,
>  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
>  	return true;
>  }
>  
> +#define MIN_MTU ETH_MIN_MTU
> +#define MAX_MTU ETH_MAX_MTU
> +

Can we drop these btw?

>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>  	int i, err;
> @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  
>  	dev->vlan_features = dev->features;
>  
> +	/* MTU range: 68 - 65535 */
> +	dev->min_mtu = MIN_MTU;
> +	dev->max_mtu = MAX_MTU;
> +
>  	/* Configuration may specify what MAC to use.  Otherwise random. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
>  		virtio_cread_bytes(vdev,
> @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>  		mtu = virtio_cread16(vdev,
>  				     offsetof(struct virtio_net_config,
>  					      mtu));
> -		if (virtnet_change_mtu(dev, mtu))
> +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)

In fact the > max_mtu branch does not make sense since a 16 bit
value can't exceed MAX_MTU.

>  			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
> +		else
> +			dev->mtu = mtu;
>  	}
>  
>  	if (vi->any_header_sg)
> diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
> index b5554f2..0c36de1 100644
> --- a/drivers/net/vmxnet3/vmxnet3_drv.c
> +++ b/drivers/net/vmxnet3/vmxnet3_drv.c
> @@ -2969,9 +2969,6 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
>  	struct vmxnet3_adapter *adapter = netdev_priv(netdev);
>  	int err = 0;
>  
> -	if (new_mtu < VMXNET3_MIN_MTU || new_mtu > VMXNET3_MAX_MTU)
> -		return -EINVAL;
> -
>  	netdev->mtu = new_mtu;
>  
>  	/*
> @@ -3428,6 +3425,10 @@ vmxnet3_probe_device(struct pci_dev *pdev,
>  	vmxnet3_set_ethtool_ops(netdev);
>  	netdev->watchdog_timeo = 5 * HZ;
>  
> +	/* MTU range: 60 - 9000 */
> +	netdev->min_mtu = VMXNET3_MIN_MTU;
> +	netdev->max_mtu = VMXNET3_MAX_MTU;
> +
>  	INIT_WORK(&adapter->work, vmxnet3_reset_work);
>  	set_bit(VMXNET3_STATE_BIT_QUIESCED, &adapter->state);
>  
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 74dc2bf..e30ffd2 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -302,7 +302,7 @@ static int xenvif_close(struct net_device *dev)
>  static int xenvif_change_mtu(struct net_device *dev, int mtu)
>  {
>  	struct xenvif *vif = netdev_priv(dev);
> -	int max = vif->can_sg ? 65535 - VLAN_ETH_HLEN : ETH_DATA_LEN;
> +	int max = vif->can_sg ? ETH_MAX_MTU - VLAN_ETH_HLEN : ETH_DATA_LEN;
>  
>  	if (mtu > max)
>  		return -EINVAL;
> @@ -471,6 +471,9 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
>  
>  	dev->tx_queue_len = XENVIF_QUEUE_LENGTH;
>  
> +	dev->min_mtu = 0;
> +	dev->max_mtu = ETH_MAX_MTU - VLAN_ETH_HLEN;
> +
>  	/*
>  	 * Initialise a dummy MAC address. We choose the numerically
>  	 * largest non-broadcast address to prevent the address getting
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index e17879d..7d616b0 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -1329,6 +1329,8 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
>  	netdev->features |= netdev->hw_features;
>  
>  	netdev->ethtool_ops = &xennet_ethtool_ops;
> +	netdev->min_mtu = 0;
> +	netdev->max_mtu = XEN_NETIF_MAX_TX_SIZE;
>  	SET_NETDEV_DEV(netdev, &dev->dev);
>  
>  	np->netdev = netdev;
> diff --git a/drivers/staging/unisys/include/iochannel.h b/drivers/staging/unisys/include/iochannel.h
> index cba4433..9081b3f 100644
> --- a/drivers/staging/unisys/include/iochannel.h
> +++ b/drivers/staging/unisys/include/iochannel.h
> @@ -113,12 +113,10 @@ enum net_types {
>  
>  };
>  
> -#define		ETH_HEADER_SIZE 14	/* size of ethernet header */
> -
>  #define		ETH_MIN_DATA_SIZE 46	/* minimum eth data size */
> -#define		ETH_MIN_PACKET_SIZE (ETH_HEADER_SIZE + ETH_MIN_DATA_SIZE)
> +#define		ETH_MIN_PACKET_SIZE (ETH_HLEN + ETH_MIN_DATA_SIZE)
>  
> -#define		ETH_MAX_MTU 16384	/* maximum data size */
> +#define		VISOR_ETH_MAX_MTU 16384	/* maximum data size */
>  
>  #ifndef MAX_MACADDR_LEN
>  #define MAX_MACADDR_LEN 6	/* number of bytes in MAC address */
> @@ -288,7 +286,7 @@ struct net_pkt_xmt {
>  	int len;	/* full length of data in the packet */
>  	int num_frags;	/* number of fragments in frags containing data */
>  	struct phys_info frags[MAX_PHYS_INFO];	/* physical page information */
> -	char ethhdr[ETH_HEADER_SIZE];	/* the ethernet header  */
> +	char ethhdr[ETH_HLEN];	/* the ethernet header  */
>  	struct {
>  		/* these are needed for csum at uisnic end */
>  		u8 valid;	/* 1 = struct is valid - else ignore */
> @@ -323,7 +321,7 @@ struct net_pkt_xmtdone {
>   */
>  #define RCVPOST_BUF_SIZE 4032
>  #define MAX_NET_RCV_CHAIN \
> -	((ETH_MAX_MTU + ETH_HEADER_SIZE + RCVPOST_BUF_SIZE - 1) \
> +	((VISOR_ETH_MAX_MTU + ETH_HLEN + RCVPOST_BUF_SIZE - 1) \
>  	/ RCVPOST_BUF_SIZE)
>  
>  struct net_pkt_rcvpost {
> diff --git a/drivers/staging/unisys/visornic/visornic_main.c b/drivers/staging/unisys/visornic/visornic_main.c
> index 1367007..f8a584b 100644
> --- a/drivers/staging/unisys/visornic/visornic_main.c
> +++ b/drivers/staging/unisys/visornic/visornic_main.c
> @@ -791,7 +791,7 @@ visornic_xmit(struct sk_buff *skb, struct net_device *netdev)
>  	 * pointing to
>  	 */
>  	firstfraglen = skb->len - skb->data_len;
> -	if (firstfraglen < ETH_HEADER_SIZE) {
> +	if (firstfraglen < ETH_HLEN) {
>  		spin_unlock_irqrestore(&devdata->priv_lock, flags);
>  		devdata->busy_cnt++;
>  		dev_err(&netdev->dev,
> @@ -864,7 +864,7 @@ visornic_xmit(struct sk_buff *skb, struct net_device *netdev)
>  	/* copy ethernet header from first frag into ocmdrsp
>  	 * - everything else will be pass in frags & DMA'ed
>  	 */
> -	memcpy(cmdrsp->net.xmt.ethhdr, skb->data, ETH_HEADER_SIZE);
> +	memcpy(cmdrsp->net.xmt.ethhdr, skb->data, ETH_HLEN);
>  	/* copy frags info - from skb->data we need to only provide access
>  	 * beyond eth header
>  	 */
> -- 
> 2.10.0

Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Jarod Wilson]

On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
> On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
...
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index fad84f3..720809f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> >  	.set_settings = virtnet_set_settings,
> >  };
> >  
> > -#define MIN_MTU 68
> > -#define MAX_MTU 65535
> > -
> > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > -{
> > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > -		return -EINVAL;
> > -	dev->mtu = new_mtu;
> > -	return 0;
> > -}
> > -
> >  static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_open            = virtnet_open,
> >  	.ndo_stop   	     = virtnet_close,
> > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
> >  	.ndo_validate_addr   = eth_validate_addr,
> >  	.ndo_set_mac_address = virtnet_set_mac_address,
> >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > -	.ndo_change_mtu	     = virtnet_change_mtu,
> >  	.ndo_get_stats64     = virtnet_stats,
> >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
> >  	return true;
> >  }
> >  
> > +#define MIN_MTU ETH_MIN_MTU
> > +#define MAX_MTU ETH_MAX_MTU
> > +
> 
> Can we drop these btw?

Bah. Yeah. Should have just used them directly. I didn't add ETH_MAX_MTU
until after doing the virtio_net changes, so I missed that.

> >  static int virtnet_probe(struct virtio_device *vdev)
> >  {
> >  	int i, err;
> > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  
> >  	dev->vlan_features = dev->features;
> >  
> > +	/* MTU range: 68 - 65535 */
> > +	dev->min_mtu = MIN_MTU;
> > +	dev->max_mtu = MAX_MTU;
> > +
> >  	/* Configuration may specify what MAC to use.  Otherwise random. */
> >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> >  		virtio_cread_bytes(vdev,
> > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> >  		mtu = virtio_cread16(vdev,
> >  				     offsetof(struct virtio_net_config,
> >  					      mtu));
> > -		if (virtnet_change_mtu(dev, mtu))
> > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
> 
> In fact the > max_mtu branch does not make sense since a 16 bit
> value can't exceed MAX_MTU.

Hm. mtu is declared as an int, not sure if there's any sort of type
promotion to be worried about (not an area I know much/anything about).
Certainly something that could be looked into as a minor optimization,
though it's only in a probe path and shouldn't hurt anything, so ... meh?

-- 
Jarod Wilson
jarod@redhat.com

Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Michael S. Tsirkin]

On Thu, Oct 20, 2016 at 10:37:20PM -0400, Jarod Wilson wrote:
> On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
> > On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
> ...
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index fad84f3..720809f 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
> > >  	.set_settings = virtnet_set_settings,
> > >  };
> > >  
> > > -#define MIN_MTU 68
> > > -#define MAX_MTU 65535
> > > -
> > > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > > -{
> > > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
> > > -		return -EINVAL;
> > > -	dev->mtu = new_mtu;
> > > -	return 0;
> > > -}
> > > -
> > >  static const struct net_device_ops virtnet_netdev = {
> > >  	.ndo_open            = virtnet_open,
> > >  	.ndo_stop   	     = virtnet_close,
> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
> > >  	.ndo_validate_addr   = eth_validate_addr,
> > >  	.ndo_set_mac_address = virtnet_set_mac_address,
> > >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
> > > -	.ndo_change_mtu	     = virtnet_change_mtu,
> > >  	.ndo_get_stats64     = virtnet_stats,
> > >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> > >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
> > >  	return true;
> > >  }
> > >  
> > > +#define MIN_MTU ETH_MIN_MTU
> > > +#define MAX_MTU ETH_MAX_MTU
> > > +
> > 
> > Can we drop these btw?
> 
> Bah. Yeah. Should have just used them directly. I didn't add ETH_MAX_MTU
> until after doing the virtio_net changes, so I missed that.
> 
> > >  static int virtnet_probe(struct virtio_device *vdev)
> > >  {
> > >  	int i, err;
> > > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >  
> > >  	dev->vlan_features = dev->features;
> > >  
> > > +	/* MTU range: 68 - 65535 */
> > > +	dev->min_mtu = MIN_MTU;
> > > +	dev->max_mtu = MAX_MTU;
> > > +
> > >  	/* Configuration may specify what MAC to use.  Otherwise random. */
> > >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
> > >  		virtio_cread_bytes(vdev,
> > > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >  		mtu = virtio_cread16(vdev,
> > >  				     offsetof(struct virtio_net_config,
> > >  					      mtu));
> > > -		if (virtnet_change_mtu(dev, mtu))
> > > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
> > 
> > In fact the > max_mtu branch does not make sense since a 16 bit
> > value can't exceed MAX_MTU.
> 
> Hm. mtu is declared as an int, not sure if there's any sort of type
> promotion to be worried about (not an area I know much/anything about).

Not by design, that's for sure.

> Certainly something that could be looked into as a minor optimization,
> though it's only in a probe path and shouldn't hurt anything, so ... meh?

Right. Aaron said he's working on a patch that essentially does
dev->max_mtu = mtu after validation, so this part will look
a bit silly there.

> -- 
> Jarod Wilson
> jarod@redhat.com

Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Wei Liu]

On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
> hyperv_net:
> - set min/max_mtu, per Haiyang, after rndis_filter_device_add
> 
> virtio_net:
> - set min/max_mtu
> - remove virtnet_change_mtu
> 
> vmxnet3:
> - set min/max_mtu
> 
> xen-netback:
> - min_mtu = 0, max_mtu = 65517
> 
> xen-netfront:
> - min_mtu = 0, max_mtu = 65535
> 
> unisys/visor:
> - clean up defines a little to not clash with network core or add
>   redundat definitions
> 
> CC: netdev@vger.kernel.org
> CC: virtualization@lists.linux-foundation.org
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Shrikrishna Khare <skhare@vmware.com>
> CC: "VMware, Inc." <pv-drivers@vmware.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Paul Durrant <paul.durrant@citrix.com>
> CC: David Kershner <david.kershner@unisys.com>
> Signed-off-by: Jarod Wilson <jarod@redhat.com>

Acked-by: Wei Liu <wei.liu2@citrix.com>

Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers

[Aaron Conole]

"Michael S. Tsirkin" <mst@redhat.com> writes:

> On Thu, Oct 20, 2016 at 10:37:20PM -0400, Jarod Wilson wrote:
>> On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
>> > On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
>> ...
>> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> > > index fad84f3..720809f 100644
>> > > --- a/drivers/net/virtio_net.c
>> > > +++ b/drivers/net/virtio_net.c
>> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>> > >  	.set_settings = virtnet_set_settings,
>> > >  };
>> > >  
>> > > -#define MIN_MTU 68
>> > > -#define MAX_MTU 65535
>> > > -
>> > > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>> > > -{
>> > > -	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
>> > > -		return -EINVAL;
>> > > -	dev->mtu = new_mtu;
>> > > -	return 0;
>> > > -}
>> > > -
>> > >  static const struct net_device_ops virtnet_netdev = {
>> > >  	.ndo_open            = virtnet_open,
>> > >  	.ndo_stop   	     = virtnet_close,
>> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
>> > >  	.ndo_validate_addr   = eth_validate_addr,
>> > >  	.ndo_set_mac_address = virtnet_set_mac_address,
>> > >  	.ndo_set_rx_mode     = virtnet_set_rx_mode,
>> > > -	.ndo_change_mtu	     = virtnet_change_mtu,
>> > >  	.ndo_get_stats64     = virtnet_stats,
>> > >  	.ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>> > >  	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
>> > > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
>> > >  	return true;
>> > >  }
>> > >  
>> > > +#define MIN_MTU ETH_MIN_MTU
>> > > +#define MAX_MTU ETH_MAX_MTU
>> > > +
>> > 
>> > Can we drop these btw?
>> 
>> Bah. Yeah. Should have just used them directly. I didn't add ETH_MAX_MTU
>> until after doing the virtio_net changes, so I missed that.
>> 
>> > >  static int virtnet_probe(struct virtio_device *vdev)
>> > >  {
>> > >  	int i, err;
>> > > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>> > >  
>> > >  	dev->vlan_features = dev->features;
>> > >  
>> > > +	/* MTU range: 68 - 65535 */
>> > > +	dev->min_mtu = MIN_MTU;
>> > > +	dev->max_mtu = MAX_MTU;
>> > > +
>> > >  	/* Configuration may specify what MAC to use.  Otherwise random. */
>> > >  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
>> > >  		virtio_cread_bytes(vdev,
>> > > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>> > >  		mtu = virtio_cread16(vdev,
>> > >  				     offsetof(struct virtio_net_config,
>> > >  					      mtu));
>> > > -		if (virtnet_change_mtu(dev, mtu))
>> > > +		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
>> > 
>> > In fact the > max_mtu branch does not make sense since a 16 bit
>> > value can't exceed MAX_MTU.
>> 
>> Hm. mtu is declared as an int, not sure if there's any sort of type
>> promotion to be worried about (not an area I know much/anything about).
>
> Not by design, that's for sure.

If you're really worried, we could declare it as a u16. The value
returned from virtio_cread16 is type u16, and there are no type
promotion rules I'm aware of that would do the wrong thing there.

>> Certainly something that could be looked into as a minor optimization,
>> though it's only in a probe path and shouldn't hurt anything, so ... meh?
>
> Right. Aaron said he's working on a patch that essentially does
> dev->max_mtu = mtu after validation, so this part will look
> a bit silly there.

Agreed, but I can do that in my patch if you don't want the extra churn.

-Aaron