linux-kernel - RE: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory barrier issue

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Date:   Sat, 8 May 2021 00:14:52 +0000
From:   Liming Sun <limings@...dia.com>
To:     Vadim Pasternak <vadimp@...dia.com>,
        Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>
Subject: RE: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory
 barrier issue

Thanks! 
Sure, I'll resent it as bugfix in v2.

> -----Original Message-----
> From: Vadim Pasternak <vadimp@...dia.com>
> Sent: Friday, May 7, 2021 11:39 AM
> To: Liming Sun <limings@...dia.com>; Andy Shevchenko
> <andy@...radead.org>; Darren Hart <dvhart@...radead.org>
> Cc: linux-kernel@...r.kernel.org; platform-driver-x86@...r.kernel.org
> Subject: RE: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory
> barrier issue
> 
> 
> 
> > -----Original Message-----
> > From: Liming Sun <limings@...dia.com>
> > Sent: Friday, May 7, 2021 6:19 PM
> > To: Andy Shevchenko <andy@...radead.org>; Darren Hart
> > <dvhart@...radead.org>; Vadim Pasternak <vadimp@...dia.com>
> > Cc: Liming Sun <limings@...dia.com>; linux-kernel@...r.kernel.org;
> > platform-driver-x86@...r.kernel.org
> > Subject: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory
> > barrier issue
> >
> > The virtio framework uses wmb() when updating avail->idx. It guarantees
> > 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.
> 
> I suppose it should be sent as Bugfix?
> 
> >
> > Signed-off-by: Liming Sun <limings@...dia.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 bbc4e71..38800e8 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);  }
> >
> > @@ -733,6 +736,12 @@ 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);
> > --
> > 1.8.3.1