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

[Simon Horman]

On Wed, Apr 02, 2025 at 07:10:18AM +0200, Michal Swiatkowski wrote:
> On Wed, Apr 02, 2025 at 12:10:37AM +0000, Harshitha Ramamurthy wrote:
> > 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;
> 
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski@xxxxxxxxxxxxxxx>
> 
> 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.

I think that would be a nice cleanup, but should be as a follow-up
to this minimal fix.

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>