ACK/Cmnt: [SRU][F:linux-bluefield][PATCH v3 1/1] UBUNTU: SAUCE: tmfifo: Fix a memory barrier issue

[Liming Sun]

Thanks for the suggestion. 
The fix solved some reported issues. Yes, I'll work on submitting it to upstream.

- Liming

> -----Original Message-----
> From: Tim Gardner <tim.gardner at canonical.com>
> Sent: Friday, May 7, 2021 10:36 AM
> To: Liming Sun <limings at nvidia.com>; kernel-team at lists.ubuntu.com
> Cc: Liming Sun <limings at nvidia.com>
> Subject: ACK/Cmnt: [SRU][F:linux-bluefield][PATCH v3 1/1] UBUNTU: SAUCE:
> tmfifo: Fix a memory barrier issue
> 
> Acked-by: Tim Gardner <tim.gardner at canonical.com>
> 
> Its unlikely to make things any worse. Should this patch be submitted
> upstream ?
> 
> On 5/6/21 6:30 AM, Liming Sun wrote:
> > From: Liming Sun <lsun at mellanox.com>
> >
> > BugLink:
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs
> .launchpad.net%2Fbugs%2F1927262&data=04%7C01%7Climings%40nvid
> ia.com%7C8506ed8979e242b6dcf608d911656ca3%7C43083d15727340c1b7db3
> 9efd9ccc17a%7C0%7C0%7C637559949579388347%7CUnknown%7CTWFpbGZs
> b3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn
> 0%3D%7C1000&sdata=1fkw63qWkMq50ceOgPpjNsxsB3ZOBHz37xMqgT
> vkypg%3D&reserved=0
> >
> > The virtio framework uses wmb() when updating avail->idx. It
> > gurantees the write order, but not necessarily loading order
> > for the code accessing the memory. This commit adds a load barrier
> > after reading the avail->idx to make sure all the data in the
> > descriptor is visible. It also adds a barrier when returning the
> > packet to virtio framework to make sure read/writes are visible to
> > the virtio code.
> >
> > Signed-off-by: Liming Sun <limings at nvidia.com>
> > ---
> >   drivers/platform/mellanox/mlxbf-tmfifo.c | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/platform/mellanox/mlxbf-tmfifo.c
> b/drivers/platform/mellanox/mlxbf-tmfifo.c
> > index 5739a966..92bda873 100644
> > --- a/drivers/platform/mellanox/mlxbf-tmfifo.c
> > +++ b/drivers/platform/mellanox/mlxbf-tmfifo.c
> > @@ -294,6 +294,9 @@ static irqreturn_t mlxbf_tmfifo_irq_handler(int irq,
> void *arg)
> >   	if (vring->next_avail == virtio16_to_cpu(vdev, vr->avail->idx))
> >   		return NULL;
> >
> > +	/* Make sure 'avail->idx' is visible already. */
> > +	virtio_rmb(false);
> > +
> >   	idx = vring->next_avail % vr->num;
> >   	head = virtio16_to_cpu(vdev, vr->avail->ring[idx]);
> >   	if (WARN_ON(head >= vr->num))
> > @@ -322,7 +325,7 @@ static void mlxbf_tmfifo_release_desc(struct
> mlxbf_tmfifo_vring *vring,
> >   	 * done or not. Add a memory barrier here to make sure the update
> above
> >   	 * completes before updating the idx.
> >   	 */
> > -	mb();
> > +	virtio_mb(false);
> >   	vr->used->idx = cpu_to_virtio16(vdev, vr_idx + 1);
> >   }
> >
> > @@ -730,6 +733,12 @@ static bool mlxbf_tmfifo_rxtx_one_desc(struct
> mlxbf_tmfifo_vring *vring,
> >   		desc = NULL;
> >   		fifo->vring[is_rx] = NULL;
> >
> > +		/*
> > +		 * Make sure the load/store are in order before
> > +		 * returning back to virtio.
> > +		 */
> > +		virtio_mb(false);
> > +
> >   		/* Notify upper layer that packet is done. */
> >   		spin_lock_irqsave(&fifo->spin_lock[is_rx], flags);
> >   		vring_interrupt(0, vring->vq);
> >
> 
> --
> -----------
> Tim Gardner
> Canonical, Inc