Date:   Mon, 1 Aug 2022 15:58:20 -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 8/1/2022 3:53 PM, Si-Wei Liu wrote:
>
>
> 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.

On destination mgmt software can run below to check vdpa mgmtdev's 
capability/features:

$ vdpa mgmtdev show pci/0000:41:04.3
pci/0000:41:04.3:
   supported_classes net
   max_supported_vqs 257
   dev_features CSUM GUEST_CSUM MTU HOST_TSO4 HOST_TSO6 STATUS CTRL_VQ 
MQ CTRL_MAC_ADDR VERSION_1 RING_PACKED
>
>>
>>
>>>
>>> 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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