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

[Michal Swiatkowski <michal.swiatkowski@linux.intel.com>]

On Wed, Apr 02, 2025 at 12:10:37AM +0000, Harshitha Ramamurthy wrote:
> From: Joshua Washington <joshwash@google.com>
> 
> 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@vger.kernel.org
> Fixes: 2c9198356d56 ("gve: Add consumed counts to ethtool stats")
> Signed-off-by: Joshua Washington <joshwash@google.com>
> Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
> ---
>  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;

Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

I will add it in gve_tx_dqo.c as num_used_tx_slots() and simplify
num_avail_tx_slots()
{
	return tx->mask - num_used_tx_slots();
}
but it isn't needed, even maybe unwanted as this is just fix.

Thanks

>  			}
>  			do {
>  				start =
> -- 
> 2.49.0.472.ge94155a9ec-goog