[PATCH net] gve: handle overflow when reporting TX consumed descriptors

[Harshitha Ramamurthy]

From: Joshua Washington <joshwash@xxxxxxxxxx>

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: stable@xxxxxxxxxxxxxxx
Fixes: 2c9198356d56 ("gve: Add consumed counts to ethtool stats")
Signed-off-by: Joshua Washington <joshwash@xxxxxxxxxx>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@xxxxxxxxxx>
---
 drivers/net/ethernet/google/gve/gve_ethtool.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/google/gve/gve_ethtool.c b/drivers/net/ethernet/google/gve/gve_ethtool.c
index 31a21ccf4863..4dea1fdce748 100644
--- a/drivers/net/ethernet/google/gve/gve_ethtool.c
+++ b/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 =
-- 
2.49.0.472.ge94155a9ec-goog