Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.34 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.34; helo=mail.nvidia.com;
Date:   Wed, 2 Jun 2021 11:57:57 +0300
From:   Eli Cohen <elic@nvidia.com>
To:     Jason Wang <jasowang@redhat.com>
CC:     <mst@redhat.com>, <virtualization@lists.linux-foundation.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] vdpa/mlx5: Only return vq ready if vq is initialized
Message-ID: <20210602085757.GA14807@mtl-vdi-166.wap.labs.mlnx>
References: <20210531160448.31537-1-elic@nvidia.com>
 <0fbd8484-9e8b-d7cc-4996-74306e6e2867@redhat.com>
 <20210601041351.GC203469@mtl-vdi-166.wap.labs.mlnx>
 <67b26a20-b418-4893-a42f-f03852c2123e@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <67b26a20-b418-4893-a42f-f03852c2123e@redhat.com>
User-Agent: Mutt/1.9.5 (bf161cf53efb) (2018-04-13)
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Jun 2021 08:58:05.5158
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: dd6724c0-e60d-43f6-20c2-08d925a48931
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT020.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4811
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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@nvidia.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,
>