linux-kernel - Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized

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Message-ID: <20210602085757.GA14807@mtl-vdi-166.wap.labs.mlnx>
Date:   Wed, 2 Jun 2021 11:57:57 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     <mst@...hat.com>, <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized

Please abandon this patch. I am sending instead a patch that resets
ready after reset.

On Tue, Jun 01, 2021 at 01:03:36PM +0800, Jason Wang wrote:
> 
> 在 2021/6/1 下午12:13, Eli Cohen 写道:
> > On Tue, Jun 01, 2021 at 10:18:04AM +0800, Jason Wang wrote:
> > > 在 2021/6/1 上午12:04, Eli Cohen 写道:
> > > > Only return the value of the ready field if the VQ is initialized in
> > > > which case the value of the field is valid.
> > > > 
> > > > Failing to do so can result in virtio_vdpa failing to load if the device
> > > > was previously used by vhost_vdpa and the old values are ready.
> > > > virtio_vdpa expects to find VQs in "not ready" state.
> > > > 
> > > > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> > > > Signed-off-by: Eli Cohen <elic@...dia.com>
> > > > ---
> > > >    drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > > index 02a05492204c..f6b680d2ab1c 100644
> > > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > > > @@ -1407,7 +1407,7 @@ static bool mlx5_vdpa_get_vq_ready(struct vdpa_device *vdev, u16 idx)
> > > >    	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> > > >    	struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[idx];
> > > > -	return mvq->ready;
> > > > +	return mvq->initialized && mvq->ready;
> > > 
> > > I think the more suitable fix is to reset mvq->ready during reset. The
> > > vq_ready should follow the queue_enable semantic in virtio-pci:
> > > 
> > > "
> > > The device MUST present a 0 in queue_enable on reset.
> > > "
> > Thinking again, I think we should call set_vq_ready() from
> > qemu/virtio_vdpa etc. after reset to explicitly set ready to false.
> 
> 
> This is not what I read from the spec and how the current driver behave.
> 
> And I don't see why we need to stick to 1 after the reset.
> 
> 
> > 
> > The ready indication is not necessairily a reflection of the hardware
> > queue:
> > 
> > "Virtual queue ready bit
> > Writing one (0x1) to this register notifies the device that it can
> > execute requests from this virtual queue. Reading from this register
> > returns the last value written to it. Both read and write accesses apply
> > to the queue selected by writing to QueueSel."
> 
> 
> My understanding that this applies if not reset in the middle. We can
> clarify this in the spec if needed.
> 
> Thanks
> 
> 
> > 
> > 
> > > Thanks
> > > 
> > > 
> > > >    }
> > > >    static int mlx5_vdpa_set_vq_state(struct vdpa_device *vdev, u16 idx,
>