On 04/22/2015 02:42 PM, Thomas Falcon wrote:

On 04/20/2015 08:07 PM, David Gibson wrote:

quoted

AFAIK the PAPR document which defines the virtual device interface used by
the ibmveth driver doesn't specify a specific maximum MTU.  So, in the

PAPR itself doesn't, but the max-frame-size property, which I understand
to be synonymous with max MTU, is required by PAPR to be present in the
Logical LAN OF node corresponding to the ibmveth device.

-Tyrel

quoted

ibmveth driver, the maximum allowed MTU is determined by the maximum
allocated buffer size of 64k (corresponding to one page in the common case)
minus the per-buffer overhead IBMVETH_BUFF_OH (which has value 22 for 14
bytes of ethernet header, plus 8 bytes for an opaque handle).

This suggests a maximum allowable MTU of 65514 bytes, but in fact the
driver only permits a maximum MTU of 65513.  This is because there is a <
instead of an <= in ibmveth_change_mtu(), which only permits an MTU which
is strictly smaller than the buffer size, rather than allowing the buffer
to be completely filled.

This patch fixes the buglet.

Thanks!

Acked-by: Thomas Falcon <redacted>

quoted

Signed-off-by: David Gibson <redacted>1
---
 drivers/net/ethernet/ibm/ibmveth.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Changes since v1:
 * Fixed a second instance of the same off-by-one error.  Thanks to
   Thomas Falcon for spotting this.

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index cd7675a..1813476 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c

@@ -1238,7 +1238,7 @@ static int ibmveth_change_mtu(struct net_device *dev, int new_mtu)
 		return -EINVAL;
 
 	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++)
-		if (new_mtu_oh < adapter->rx_buff_pool[i].buff_size)
+		if (new_mtu_oh <= adapter->rx_buff_pool[i].buff_size)
 			break;
 
 	if (i == IBMVETH_NUM_BUFF_POOLS)

@@ -1257,7 +1257,7 @@ static int ibmveth_change_mtu(struct net_device *dev, int new_mtu)
 	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++) {
 		adapter->rx_buff_pool[i].active = 1;
 
-		if (new_mtu_oh < adapter->rx_buff_pool[i].buff_size) {
+		if (new_mtu_oh <= adapter->rx_buff_pool[i].buff_size) {
 			dev->mtu = new_mtu;
 			vio_cmo_set_dev_desired(viodev,
 						ibmveth_get_desired_dma

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