netdev - Re: [PATCHv6 net-next 2/3] sunvnet: allow admin to set sunvnet MTU

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Date:	Wed, 17 Sep 2014 21:19:27 -0700
From:	Raghuram Kothakota <Raghuram.Kothakota@...cle.com>
To:	David L Stevens <david.stevens@...cle.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCHv6 net-next 2/3] sunvnet: allow admin to set sunvnet MTU


On Sep 17, 2014, at 5:10 PM, David L Stevens <david.stevens@...cle.com> wrote:

> This patch allows an admin to set the MTU on a sunvnet device to arbitrary
> values between the minimum (68) and maximum (65535) IPv4 packet sizes.
> 
> Signed-off-by: David L Stevens <david.stevens@...cle.com>
> ---
> arch/sparc/kernel/ldc.c            |    2 +-
> drivers/net/ethernet/sun/sunvnet.c |    7 +++++--
> drivers/net/ethernet/sun/sunvnet.h |    6 ++++--
> 3 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/sparc/kernel/ldc.c b/arch/sparc/kernel/ldc.c
> index 66dacd5..0af28b9 100644
> --- a/arch/sparc/kernel/ldc.c
> +++ b/arch/sparc/kernel/ldc.c
> @@ -2159,7 +2159,7 @@ int ldc_map_single(struct ldc_channel *lp,
> 	state.pte_idx = (base - iommu->page_table);
> 	state.nc = 0;
> 	fill_cookies(&state, (pa & PAGE_MASK), (pa & ~PAGE_MASK), len);
> -	BUG_ON(state.nc != 1);
> +	BUG_ON(state.nc > ncookies);
> 
> 	return state.nc;
> }
> diff --git a/drivers/net/ethernet/sun/sunvnet.c b/drivers/net/ethernet/sun/sunvnet.c
> index a9638c1..5e64e60 100644
> --- a/drivers/net/ethernet/sun/sunvnet.c
> +++ b/drivers/net/ethernet/sun/sunvnet.c
> @@ -791,6 +791,9 @@ static int vnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> 	if (unlikely(!port))
> 		goto out_dropped;
> 
> +	if (skb->len > port->rmtu)
> +		goto out_dropped;
> +
> 	spin_lock_irqsave(&port->vio.lock, flags);
> 
> 	dr = &port->vio.drings[VIO_DRIVER_TX_RING];
> @@ -1038,7 +1041,7 @@ static void vnet_set_rx_mode(struct net_device *dev)
> 
> static int vnet_change_mtu(struct net_device *dev, int new_mtu)
> {
> -	if (new_mtu != ETH_DATA_LEN)
> +	if (new_mtu < 68 || new_mtu > 65535)
> 		return -EINVAL;
> 


FYI, LDoms manager provides the maximum MTU of packets allowed for
a vnet device in the "virtual-device" MD node corresponding to the vnet device.
The virtual switch is expected to enforce that size for packets that go through
it. Ideally we want a Guest OS to honor that MTU setting as well, which is probably
not the case here. LDoms manager doesn't allow setting more than 16K today,
I guess this code is ignoring this for Guest to Guest communication.

-Raghuram

> 	dev->mtu = new_mtu;
> @@ -1131,7 +1134,7 @@ static int vnet_port_alloc_tx_bufs(struct vnet_port *port)
> 		}
> 
> 		err = ldc_map_single(port->vio.lp, buf, map_len,
> -				     port->tx_bufs[i].cookies, 2,
> +				     port->tx_bufs[i].cookies, VNET_MAXCOOKIES,
> 				     (LDC_MAP_SHADOW |
> 				      LDC_MAP_DIRECT |
> 				      LDC_MAP_RW));
> diff --git a/drivers/net/ethernet/sun/sunvnet.h b/drivers/net/ethernet/sun/sunvnet.h
> index 986e04b..a39a801 100644
> --- a/drivers/net/ethernet/sun/sunvnet.h
> +++ b/drivers/net/ethernet/sun/sunvnet.h
> @@ -11,7 +11,7 @@
>  */
> #define VNET_TX_TIMEOUT			(5 * HZ)
> 
> -#define VNET_MAXPACKET			1518ULL /* ETH_FRAMELEN + VLAN_HDR */
> +#define VNET_MAXPACKET			(65535ULL + ETH_HLEN + VLAN_HLEN)
> #define VNET_TX_RING_SIZE		512
> #define VNET_TX_WAKEUP_THRESH(dr)	((dr)->pending / 4)
> 
> @@ -21,10 +21,12 @@
>  */
> #define VNET_PACKET_SKIP		6
> 
> +#define VNET_MAXCOOKIES			(VNET_MAXPACKET/PAGE_SIZE + 1)
> +
> struct vnet_tx_entry {
> 	void			*buf;
> 	unsigned int		ncookies;
> -	struct ldc_trans_cookie	cookies[2];
> +	struct ldc_trans_cookie	cookies[VNET_MAXCOOKIES];
> };
> 
> struct vnet;
> -- 
> 1.7.1
> 
> --
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