Michael S. Tsirkin
2020-Dec-09 06:46 UTC
[PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index
On Wed, Dec 09, 2020 at 08:02:30AM +0200, Eli Cohen wrote:> On Tue, Dec 08, 2020 at 04:45:04PM -0500, Michael S. Tsirkin wrote: > > On Sun, Dec 06, 2020 at 12:57:19PM +0200, Eli Cohen wrote: > > > Make sure to put write memory barrier after updating CQ consumer index > > > so the hardware knows that there are available CQE slots in the queue. > > > > > > Failure to do this can cause the update of the RX doorbell record to get > > > updated before the CQ consumer index resulting in CQ overrun. > > > > > > Change-Id: Ib0ae4c118cce524c9f492b32569179f3c1f04cc1 > > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices") > > > Signed-off-by: Eli Cohen <elic at nvidia.com> > > > > Aren't both memory writes? > > Not sure what exactly you mean here.Both updates are CPU writes into RAM that hardware then reads using DMA.> > And given that, isn't dma_wmb() sufficient here? > > I agree that dma_wmb() is more appropriate here. > > > > > > > > --- > > > drivers/vdpa/mlx5/net/mlx5_vnet.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > index 1f4089c6f9d7..295f46eea2a5 100644 > > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c > > > @@ -478,6 +478,11 @@ static int mlx5_vdpa_poll_one(struct mlx5_vdpa_cq *vcq) > > > static void mlx5_vdpa_handle_completions(struct mlx5_vdpa_virtqueue *mvq, int num) > > > { > > > mlx5_cq_set_ci(&mvq->cq.mcq); > > > + > > > + /* make sure CQ cosumer update is visible to the hardware before updating > > > + * RX doorbell record. > > > + */ > > > + wmb(); > > > rx_post(&mvq->vqqp, num); > > > if (mvq->event_cb.callback) > > > mvq->event_cb.callback(mvq->event_cb.private); > > > -- > > > 2.27.0 > >