在 2022/7/30 04:55, Si-Wei Liu 写道:

On 7/28/2022 7:04 PM, Zhu, Lingshan wrote:

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On 7/29/2022 5:48 AM, Si-Wei Liu wrote:

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On 7/27/2022 7:43 PM, Zhu, Lingshan wrote:

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On 7/28/2022 8:56 AM, Si-Wei Liu wrote:

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On 7/27/2022 4:47 AM, Zhu, Lingshan wrote:

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On 7/27/2022 5:43 PM, Si-Wei Liu wrote:

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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

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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.

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

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Thanks
Zhu Lingshan

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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.

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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:

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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

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Thanks,
-Siwei

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Regards,
-Siwei

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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.

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Thanks,
-Siwei

On 7/1/2022 3:12 PM, Parav Pandit via Virtualization wrote:

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From: Zhu Lingshan<redacted>
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.

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Signed-off-by: Zhu Lingshan<redacted>
---
  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

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