netdev - Re: [PATCH V3 6/6] vDPA: fix 'cast to restricted le16' warnings in vdpa.c

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Date:   Mon, 1 Aug 2022 12:33:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        "Zhu, Lingshan" <lingshan.zhu@...el.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        parav@...dia.com, xieyongji@...edance.com, gautam.dawar@....com
Subject: Re: [PATCH V3 6/6] vDPA: fix 'cast to restricted le16' warnings in
 vdpa.c


在 2022/7/29 17:39, Michael S. Tsirkin 写道:
> On Fri, Jul 29, 2022 at 05:35:09PM +0800, Zhu, Lingshan wrote:
>>
>> On 7/29/2022 5:23 PM, Michael S. Tsirkin wrote:
>>> On Fri, Jul 29, 2022 at 05:20:17PM +0800, Zhu, Lingshan wrote:
>>>> On 7/29/2022 5:17 PM, Michael S. Tsirkin wrote:
>>>>> On Fri, Jul 29, 2022 at 05:07:11PM +0800, Zhu, Lingshan wrote:
>>>>>> On 7/29/2022 4:53 PM, Michael S. Tsirkin wrote:
>>>>>>> On Fri, Jul 01, 2022 at 09:28:26PM +0800, Zhu Lingshan wrote:
>>>>>>>> This commit fixes spars warnings: cast to restricted __le16
>>>>>>>> in function vdpa_dev_net_config_fill() and
>>>>>>>> vdpa_fill_stats_rec()
>>>>>>>>
>>>>>>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>>>>>>>> ---
>>>>>>>>      drivers/vdpa/vdpa.c | 6 +++---
>>>>>>>>      1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
>>>>>>>> index 846dd37f3549..ed49fe46a79e 100644
>>>>>>>> --- a/drivers/vdpa/vdpa.c
>>>>>>>> +++ b/drivers/vdpa/vdpa.c
>>>>>>>> @@ -825,11 +825,11 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
>>>>>>>>      		    config.mac))
>>>>>>>>      		return -EMSGSIZE;
>>>>>>>> -	val_u16 = le16_to_cpu(config.status);
>>>>>>>> +	val_u16 = __virtio16_to_cpu(true, config.status);
>>>>>>>>      	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_STATUS, val_u16))
>>>>>>>>      		return -EMSGSIZE;
>>>>>>>> -	val_u16 = le16_to_cpu(config.mtu);
>>>>>>>> +	val_u16 = __virtio16_to_cpu(true, config.mtu);
>>>>>>>>      	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
>>>>>>>>      		return -EMSGSIZE;
>>>>>>> Wrong on BE platforms with legacy interface, isn't it?
>>>>>>> We generally don't handle legacy properly in VDPA so it's
>>>>>>> not a huge deal, but maybe add a comment at least?
>>>>>> Sure, I can add a comment here: this is for modern devices only.
>>>>>>
>>>>>> Thanks,
>>>>>> Zhu Lingshan
>>>>> Hmm. what "this" is for modern devices only here?
>>>> this cast, for LE modern devices.
>>> I think status existed in legacy for sure, and it's possible that
>>> some legacy devices backported mtu and max_virtqueue_pairs otherwise
>>> we would have these fields as __le not as __virtio, right?
>> yes, that's the reason why it is virtio_16 than just le16.
>>
>> I may find a better solution to detect whether it is LE, or BE without a
>> virtio_dev structure.
>> Check whether vdpa_device->get_device_features() has VIRTIO_F_VERISON_1. If
>> the device offers _F_VERSION_1, then it is a LE device,
>> or it is a BE device, then we use __virtio16_to_cpu(false, config.status).
>>
>> Does this look good?
> No since the question is can be a legacy driver with a transitional
> device.  I don't have a good idea yet. vhost has VHOST_SET_VRING_ENDIAN
> and maybe we need something like this for config as well?


Not sure, and even if we had this, the query could happen before 
VHOST_SET_VRING_ENDIAN.

Actually, the patch should be fine itself, since the issue exist even 
before the patch (which assumes a le).

Thanks


>
>>>>>>>> @@ -911,7 +911,7 @@ static int vdpa_fill_stats_rec(struct vdpa_device *vdev, struct sk_buff *msg,
>>>>>>>>      	}
>>>>>>>>      	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
>>>>>>>> -	max_vqp = le16_to_cpu(config.max_virtqueue_pairs);
>>>>>>>> +	max_vqp = __virtio16_to_cpu(true, config.max_virtqueue_pairs);
>>>>>>>>      	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP, max_vqp))
>>>>>>>>      		return -EMSGSIZE;
>>>>>>>> -- 
>>>>>>>> 2.31.1