Date:   Mon, 1 Aug 2022 15:53:37 -0700
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     Jason Wang <jasowang@...hat.com>,
        "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        Parav Pandit <parav@...dia.com>,
        "mst@...hat.com" <mst@...hat.com>, Eli Cohen <elic@...dia.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH V3 4/6] vDPA: !FEATURES_OK should not block querying
 device config space



On 7/31/2022 9:44 PM, Jason Wang wrote:
>
> 在 2022/7/30 04:55, Si-Wei Liu 写道:
>>
>>
>> On 7/28/2022 7:04 PM, Zhu, Lingshan wrote:
>>>
>>>
>>> On 7/29/2022 5:48 AM, Si-Wei Liu wrote:
>>>>
>>>>
>>>> On 7/27/2022 7:43 PM, Zhu, Lingshan wrote:
>>>>>
>>>>>
>>>>> On 7/28/2022 8:56 AM, Si-Wei Liu wrote:
>>>>>>
>>>>>>
>>>>>> On 7/27/2022 4:47 AM, Zhu, Lingshan wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 7/27/2022 5:43 PM, Si-Wei Liu wrote:
>>>>>>>> Sorry to chime in late in the game. For some reason I couldn't 
>>>>>>>> get to most emails for this discussion (I only subscribed to 
>>>>>>>> the virtualization list), while I was taking off amongst the 
>>>>>>>> past few weeks.
>>>>>>>>
>>>>>>>> It looks to me this patch is incomplete. Noted down the way in 
>>>>>>>> vdpa_dev_net_config_fill(), we have the following:
>>>>>>>>          features = vdev->config->get_driver_features(vdev);
>>>>>>>>          if (nla_put_u64_64bit(msg, 
>>>>>>>> VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features,
>>>>>>>>                                VDPA_ATTR_PAD))
>>>>>>>>                  return -EMSGSIZE;
>>>>>>>>
>>>>>>>> Making call to .get_driver_features() doesn't make sense when 
>>>>>>>> feature negotiation isn't complete. Neither should present 
>>>>>>>> negotiated_features to userspace before negotiation is done.
>>>>>>>>
>>>>>>>> Similarly, max_vqp through vdpa_dev_net_mq_config_fill() 
>>>>>>>> probably should not show before negotiation is done - it 
>>>>>>>> depends on driver features negotiated.
>>>>>>> I have another patch in this series introduces device_features 
>>>>>>> and will report device_features to the userspace even features 
>>>>>>> negotiation not done. Because the spec says we should allow 
>>>>>>> driver access the config space before FEATURES_OK.
>>>>>> The config space can be accessed by guest before features_ok 
>>>>>> doesn't necessarily mean the value is valid. You may want to 
>>>>>> double check with Michael for what he quoted earlier:
>>>>> that's why I proposed to fix these issues, e.g., if no _F_MAC, 
>>>>> vDPA kernel should not return a mac to the userspace, there is not 
>>>>> a default value for mac.
>>>> Then please show us the code, as I can only comment based on your 
>>>> latest (v4) patch and it was not there.. To be honest, I don't 
>>>> understand the motivation and the use cases you have, is it for 
>>>> debugging/monitoring or there's really a use case for live 
>>>> migration? For the former, you can do a direct dump on all config 
>>>> space fields regardless of endianess and feature negotiation 
>>>> without having to worry about validity (meaningful to present to 
>>>> admin user). To me these are conflict asks that is impossible to 
>>>> mix in exact one command.
>>> This bug just has been revealed two days, and you will see the patch 
>>> soon.
>>>
>>> There are something to clarify:
>>> 1) we need to read the device features, or how can you pick a proper 
>>> LM destination
>
>
> So it's probably not very efficient to use this, the manager layer 
> should have the knowledge about the compatibility before doing 
> migration other than try-and-fail.
>
> And it's the task of the management to gather the nodes whose devices 
> could be live migrated to each other as something like "cluster" which 
> we've already used in the case of cpuflags.
>
> 1) during node bootstrap, the capability of each node and devices was 
> reported to management layer
> 2) management layer decide the cluster and make sure the migration can 
> only done among the nodes insides the cluster
> 3) before migration, the vDPA needs to be provisioned on the destination
>
>
>>> 2) vdpa dev config show can show both device features and driver 
>>> features, there just need a patch for iproute2
>>> 3) To process information like MQ, we don't just dump the config 
>>> space, MST has explained before
>> So, it's for live migration... Then why not export those config 
>> parameters specified for vdpa creation (as well as device feature 
>> bits) to the output of "vdpa dev show" command? That's where device 
>> side config lives and is static across vdpa's life cycle. "vdpa dev 
>> config show" is mostly for dynamic driver side config, and the 
>> validity is subject to feature negotiation. I suppose this should 
>> suit your need of LM, e.g.
>
>
> I think so.
>
>
>>
>> $ vdpa dev add name vdpa1 mgmtdev pci/0000:41:04.2 max_vqp 7 mtu 2000
>> $ vdpa dev show vdpa1
>> vdpa1: type network mgmtdev pci/0000:41:04.2 vendor_id 5555 max_vqs 
>> 15 max_vq_size 256
>>   max_vqp 7 mtu 2000
>>   dev_features CSUM GUEST_CSUM MTU HOST_TSO4 HOST_TSO6 STATUS CTRL_VQ 
>> MQ CTRL_MAC_ADDR VERSION_1 RING_PACKED
>
>
> Note that the mgmt should know this destination have those 
> capability/features before the provisioning.
Yes, mgmt software should have to check the above from source.

>
>
>>
>> For it to work, you'd want to pass "struct vdpa_dev_set_config" to 
>> _vdpa_register_device() during registration, and get it saved there 
>> in "struct vdpa_device". Then in vdpa_dev_fill() show each field 
>> conditionally subject to "struct vdpa_dev_set_config.mask".
>>
>> Thanks,
>> -Siwei
>
>
> Thanks
>
>
>>>
>>> Thanks
>>> Zhu Lingshan
>>>>
>>>>>>> Nope:
>>>>>>>
>>>>>>> 2.5.1  Driver Requirements: Device Configuration Space
>>>>>>>
>>>>>>> ...
>>>>>>>
>>>>>>> For optional configuration space fields, the driver MUST check 
>>>>>>> that the corresponding feature is offered
>>>>>>> before accessing that part of the configuration space.
>>>>>>
>>>>>> and how many driver bugs taking wrong assumption of the validity 
>>>>>> of config space field without features_ok. I am not sure what use 
>>>>>> case you want to expose config resister values for before 
>>>>>> features_ok, if it's mostly for live migration I guess it's 
>>>>>> probably heading a wrong direction.
>>>>>>
>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Last but not the least, this "vdpa dev config" command was not 
>>>>>>>> designed to display the real config space register values in 
>>>>>>>> the first place. Quoting the vdpa-dev(8) man page:
>>>>>>>>
>>>>>>>>> vdpa dev config show - Show configuration of specific device 
>>>>>>>>> or all devices.
>>>>>>>>> DEV - specifies the vdpa device to show its configuration. If 
>>>>>>>>> this argument is omitted all devices configuration is listed.
>>>>>>>> It doesn't say anything about configuration space or register 
>>>>>>>> values in config space. As long as it can convey the config 
>>>>>>>> attribute when instantiating vDPA device instance, and more 
>>>>>>>> importantly, the config can be easily imported from or exported 
>>>>>>>> to userspace tools when trying to reconstruct vdpa instance 
>>>>>>>> intact on destination host for live migration, IMHO in my 
>>>>>>>> personal interpretation it doesn't matter what the config space 
>>>>>>>> may present. It may be worth while adding a new debug command 
>>>>>>>> to expose the real register value, but that's another story.
>>>>>>> I am not sure getting your points. vDPA now reports device 
>>>>>>> feature bits(device_features) and negotiated feature 
>>>>>>> bits(driver_features), and yes, the drivers features can be a 
>>>>>>> subset of the device features; and the vDPA device features can 
>>>>>>> be a subset of the management device features.
>>>>>> What I said is after unblocking the conditional check, you'd have 
>>>>>> to handle the case for each of the vdpa attribute when feature 
>>>>>> negotiation is not yet done: basically the register values you 
>>>>>> got from config space via the vdpa_get_config_unlocked() call is 
>>>>>> not considered to be valid before features_ok (per-spec). 
>>>>>> Although in some case you may get sane value, such behavior is 
>>>>>> generally undefined. If you desire to show just the 
>>>>>> device_features alone without any config space field, which the 
>>>>>> device had advertised *before feature negotiation is complete*, 
>>>>>> that'll be fine. But looks to me this is not how patch has been 
>>>>>> implemented. Probably need some more work?
>>>>> They are driver_features(negotiated) and the device_features(which 
>>>>> comes with the device), and the config space fields that depend on 
>>>>> them. In this series, we report both to the userspace.
>>>> I fail to understand what you want to present from your 
>>>> description. May be worth showing some example outputs that at 
>>>> least include the following cases: 1) when device offers features 
>>>> but not yet acknowledge by guest 2) when guest acknowledged 
>>>> features and device is yet to accept 3) after guest feature 
>>>> negotiation is completed (agreed upon between guest and device).
>>> Only two feature sets: 1) what the device has. (2) what is negotiated
>>>>
>>>> Thanks,
>>>> -Siwei
>>>>>>
>>>>>> Regards,
>>>>>> -Siwei
>>>>>>
>>>>>>>>
>>>>>>>> Having said, please consider to drop the Fixes tag, as appears 
>>>>>>>> to me you're proposing a new feature rather than fixing a real 
>>>>>>>> issue.
>>>>>>> it's a new feature to report the device feature bits than only 
>>>>>>> negotiated features, however this patch is a must, or it will 
>>>>>>> block the device feature bits reporting. but I agree, the fix 
>>>>>>> tag is not a must.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> -Siwei
>>>>>>>>
>>>>>>>> On 7/1/2022 3:12 PM, Parav Pandit via Virtualization wrote:
>>>>>>>>>> From: Zhu Lingshan<lingshan.zhu@...el.com>
>>>>>>>>>> Sent: Friday, July 1, 2022 9:28 AM
>>>>>>>>>>
>>>>>>>>>> Users may want to query the config space of a vDPA device, to 
>>>>>>>>>> choose a
>>>>>>>>>> appropriate one for a certain guest. This means the users 
>>>>>>>>>> need to read the
>>>>>>>>>> config space before FEATURES_OK, and the existence of config 
>>>>>>>>>> space
>>>>>>>>>> contents does not depend on FEATURES_OK.
>>>>>>>>>>
>>>>>>>>>> The spec says:
>>>>>>>>>> The device MUST allow reading of any device-specific 
>>>>>>>>>> configuration field
>>>>>>>>>> before FEATURES_OK is set by the driver. This includes fields 
>>>>>>>>>> which are
>>>>>>>>>> conditional on feature bits, as long as those feature bits 
>>>>>>>>>> are offered by the
>>>>>>>>>> device.
>>>>>>>>>>
>>>>>>>>>> Fixes: 30ef7a8ac8a07 (vdpa: Read device configuration only if 
>>>>>>>>>> FEATURES_OK)
>>>>>>>>> Fix is fine, but fixes tag needs correction described below.
>>>>>>>>>
>>>>>>>>> Above commit id is 13 letters should be 12.
>>>>>>>>> And
>>>>>>>>> It should be in format
>>>>>>>>> Fixes: 30ef7a8ac8a0 ("vdpa: Read device configuration only if 
>>>>>>>>> FEATURES_OK")
>>>>>>>>>
>>>>>>>>> Please use checkpatch.pl script before posting the patches to 
>>>>>>>>> catch these errors.
>>>>>>>>> There is a bot that looks at the fixes tag and identifies the 
>>>>>>>>> right kernel version to apply this fix.
>>>>>>>>>
>>>>>>>>>> Signed-off-by: Zhu Lingshan<lingshan.zhu@...el.com>
>>>>>>>>>> ---
>>>>>>>>>>   drivers/vdpa/vdpa.c | 8 --------
>>>>>>>>>>   1 file changed, 8 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index
>>>>>>>>>> 9b0e39b2f022..d76b22b2f7ae 100644
>>>>>>>>>> --- a/drivers/vdpa/vdpa.c
>>>>>>>>>> +++ b/drivers/vdpa/vdpa.c
>>>>>>>>>> @@ -851,17 +851,9 @@ vdpa_dev_config_fill(struct vdpa_device 
>>>>>>>>>> *vdev,
>>>>>>>>>> struct sk_buff *msg, u32 portid,  {
>>>>>>>>>>       u32 device_id;
>>>>>>>>>>       void *hdr;
>>>>>>>>>> -    u8 status;
>>>>>>>>>>       int err;
>>>>>>>>>>
>>>>>>>>>>       down_read(&vdev->cf_lock);
>>>>>>>>>> -    status = vdev->config->get_status(vdev);
>>>>>>>>>> -    if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
>>>>>>>>>> -        NL_SET_ERR_MSG_MOD(extack, "Features negotiation not
>>>>>>>>>> completed");
>>>>>>>>>> -        err = -EAGAIN;
>>>>>>>>>> -        goto out;
>>>>>>>>>> -    }
>>>>>>>>>> -
>>>>>>>>>>       hdr = genlmsg_put(msg, portid, seq, &vdpa_nl_family, 
>>>>>>>>>> flags,
>>>>>>>>>>                 VDPA_CMD_DEV_CONFIG_GET);
>>>>>>>>>>       if (!hdr) {
>>>>>>>>>> -- 
>>>>>>>>>> 2.31.1
>>>>>>>>> _______________________________________________
>>>>>>>>> Virtualization mailing list
>>>>>>>>> Virtualization@...ts.linux-foundation.org
>>>>>>>>> https://urldefense.com/v3/__https://lists.linuxfoundation.org/mailman/listinfo/virtualization__;!!ACWV5N9M2RV99hQ!NzOv5Ew_Z2CP-zHyD7RsUoStLZ54KpB21QyuZ8L63YVPLEGDEwvcOSDlIGxQPHY-DMkOa9sKKZdBSaNknMU$ 
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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