gve: handle overflow when reporting TX consumed descriptors

commit 15970e1 upstream.

When the tx tail is less than the head (in cases of wraparound), the TX
consumed descriptor statistic in DQ will be reported as
UINT32_MAX - head + tail, which is incorrect. Mask the difference of
head and tail according to the ring size when reporting the statistic.

Cc: [email protected]
Fixes: 2c91983 ("gve: Add consumed counts to ethtool stats")
Signed-off-by: Joshua Washington <[email protected]>
Signed-off-by: Harshitha Ramamurthy <[email protected]>
Reviewed-by: Michal Swiatkowski <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: josh8551021

drivers/net/ethernet/google/gve/gve_ethtool.c

@@ -392,7 +392,9 @@ gve_get_ethtool_stats(struct net_device *netdev,
 				 */
 				data[i++] = 0;
 				data[i++] = 0;
-				data[i++] = tx->dqo_tx.tail - tx->dqo_tx.head;
+				data[i++] =
+					(tx->dqo_tx.tail - tx->dqo_tx.head) &
+					tx->mask;
 			}
 			do {
 				start =