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[79.176.44.197]) by smtp.gmail.com with ESMTPSA id n17sm99784wmc.33.2020.12.08.13.45.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Dec 2020 13:45:07 -0800 (PST) Date: Tue, 8 Dec 2020 16:45:04 -0500 From: "Michael S. Tsirkin" To: Eli Cohen Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, lulu@redhat.com Subject: Re: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index Message-ID: <20201208164356-mutt-send-email-mst@kernel.org> References: <20201206105719.123753-1-elic@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201206105719.123753-1-elic@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Aren't both memory writes? And given that, isn't dma_wmb() sufficient 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