Re: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning

[Si-Wei Liu <si-wei.liu@oracle.com>]

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On 9/26/2022 12:11 AM, Jason Wang wrote:
> On Sat, Sep 24, 2022 at 4:01 AM Si-Wei Liu<si-wei.liu@oracle.com>  wrote:
>>
>>
>> On 9/21/2022 7:43 PM, Jason Wang wrote:
>>> This patch implements features provisioning for vdpa_sim_net.
>>>
>>> 1) validating the provisioned features to be a subset of the parent
>>>      features.
>>> 2) clearing the features that is not wanted by the userspace
>>>
>>> For example:
>>>
>>> # vdpa mgmtdev show
>>> vdpasim_net:
>>>     supported_classes net
>>>     max_supported_vqs 3
>>>     dev_features MTU MAC CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT VERSION_1 ACCESS_PLATFORM
>> Sighs, not to blame any one and it's perhaps too late, but this
>> "dev_features" attr in "mgmtdev show" command output should have been
>> called "supported_features" in the first place.
> Not sure I get this, but I guess this is the negotiated features actually.
Actually no, that is why I said the name is a bit confusing and 
"supported_features" might sound better. This attribute in the parent 
device (mgmtdev) denotes the real device capability for what virtio 
features can be supported by the parent device. Any unprivileged user 
can check into this field to know parent device's capability without 
having to create a child vDPA device at all. The features that child 
vDPA device may support should be a subset of, or at most up to what the 
parent device offers. For e.g. the vdpa device dev1 you created below 
can expose less or equal device_features bit than 0x308820028 (MTU MAC 
CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT VERSION_1 ACCESS_PLATFORM), but 
shouldn't be no more than what the parent device can actually support.

>
> I think Ling Shan is working on reporting both negotiated features
> with the device features.
Does it imply this series is connected to another work in parallel? Is 
it possible to add a reference in the cover letter?

>
>>> 1) provision vDPA device with all features that are supported by the
>>>      net simulator
>>>
>>> # vdpa dev add name dev1 mgmtdev vdpasim_net
>>> # vdpa dev config show
>>> dev1: mac 00:00:00:00:00:00 link up link_announce false mtu 1500
>>>     negotiated_features MTU MAC CTRL_VQ CTRL_MAC_ADDR VERSION_1 ACCESS_PLATFORM
>> Maybe not in this patch, but for completeness for the whole series,
>> could we also add device_features to the output?
> Lingshan, could you please share your thoughts or patch on this?
Noted here the device_features argument specified during vdpa creation 
is introduced by this series itself, it somehow slightly changed the 
original semantics of what device_features used to be.

>
>> When simply look at the "vdpa dev config show" output, I cannot really
>> tell the actual device_features that was used in vdpa creation. For e.g.
>> there is a missing feature ANY_LAYOUT from negotiated_features compared
>> with supported_features in mgmtdev, but the orchestration software
>> couldn't tell if the vdpa device on destination host should be created
>> with or without the ANY_LAYOUT feature.
> I think VERSION_1 implies ANY_LAYOUT.
Right, ANY_LAYOUT is a bad example. A good example might be that, I knew 
the parent mgmtdev on migration source node supports CTRL_MAC_ADDR, but 
I don't find it in negotiated_features. On the migration destination 
node, the parent device does support all features as the source offers, 
including CTRL_MAC_ADDR. What device features you would expect the mgmt 
software to create destination vdpa device with, if not otherwise 
*requiring mgmt software to remember all the arguments on device creation*?

SOURCE# vdpa mgmtdev show
vdpasim_net:
    supported_classes net
    max_supported_vqs 3
    dev_features MTU MAC CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT VERSION_1 
ACCESS_PLATFORM
SOURCE# vdpa dev config show
dev1: mac 00:00:00:00:00:00 link up link_announce false mtu 1500
    negotiated_features MTU MAC CTRL_VQ VERSION_1 ACCESS_PLATFORM

DESTINATION# vdpa mgmtdev show
vdpasim_net:
    supported_classes net
    max_supported_vqs 3
    dev_features MTU MAC CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT VERSION_1 
ACCESS_PLATFORM

>   But it should be sufficient to
> use features_src & feature_dst in this case. Actually, it should work
> similar as to the cpu flags, the management software should introduce
> the concept of cluster which means the maximal set of common features
> is calculated and provisioned during device creation to allow
> migration among the nodes inside the cluster.
Yes, this is one way mgmt software may implement, but I am not sure if 
it's the only way. For e.g. for cpu flags, mgmt software can infer the 
guest cpus features in use from all qemu command line arguments and host 
cpu features/capability, which doesn't need to remember creation 
arguments and is easy to recover from failure without having to make the 
VM config persistent in data store. I thought it would be great if vdpa 
CLI design could offer the same.

Thanks,
-Siwei

>
> Thanks
>
>> Thanks,
>> -Siwei
>>
>>
>>> 2) provision vDPA device with a subset of the features
>>>
>>> # vdpa dev add name dev1 mgmtdev vdpasim_net device_features 0x300020000
>>> # vdpa dev config show
>>> dev1: mac 00:00:00:00:00:00 link up link_announce false mtu 1500
>>>     negotiated_features CTRL_VQ VERSION_1 ACCESS_PLATFORM
>>>
>>> Reviewed-by: Eli Cohen<elic@nvidia.com>
>>> Signed-off-by: Jason Wang<jasowang@redhat.com>
>>> ---
>>>    drivers/vdpa/vdpa_sim/vdpa_sim_net.c | 11 ++++++++++-
>>>    1 file changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>> index 886449e88502..a9ba02be378b 100644
>>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>> @@ -254,6 +254,14 @@ static int vdpasim_net_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
>>>        dev_attr.work_fn = vdpasim_net_work;
>>>        dev_attr.buffer_size = PAGE_SIZE;
>>>
>>> +     if (config->mask & BIT_ULL(VDPA_ATTR_DEV_FEATURES)) {
>>> +             if (config->device_features &
>>> +                 ~dev_attr.supported_features)
>>> +                     return -EINVAL;
>>> +             dev_attr.supported_features &=
>>> +                      config->device_features;
>>> +     }
>>> +
>>>        simdev = vdpasim_create(&dev_attr);
>>>        if (IS_ERR(simdev))
>>>                return PTR_ERR(simdev);
>>> @@ -294,7 +302,8 @@ static struct vdpa_mgmt_dev mgmt_dev = {
>>>        .id_table = id_table,
>>>        .ops = &vdpasim_net_mgmtdev_ops,
>>>        .config_attr_mask = (1 << VDPA_ATTR_DEV_NET_CFG_MACADDR |
>>> -                          1 << VDPA_ATTR_DEV_NET_CFG_MTU),
>>> +                          1 << VDPA_ATTR_DEV_NET_CFG_MTU |
>>> +                          1 << VDPA_ATTR_DEV_FEATURES),
>>>        .max_supported_vqs = VDPASIM_NET_VQ_NUM,
>>>        .supported_features = VDPASIM_NET_FEATURES,
>>>    };

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