Re: [PATCH v4 11/12] vfio/migration: Don't block migration device dirty tracking is unsupported

[Joao Martins <joao.m.martins@oracle.com>]

On 17/07/2024 16:35, Joao Martins wrote:
> On 17/07/2024 10:20, Joao Martins wrote:
>> On 17/07/2024 03:38, Duan, Zhenzhong wrote:
>>>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>>>> index 34d4be2ce1b1..ce3d1b6e9a25 100644
>>>> --- a/hw/vfio/migration.c
>>>> +++ b/hw/vfio/migration.c
>>>> @@ -1036,7 +1036,8 @@ bool vfio_migration_realize(VFIODevice
>>>> *vbasedev, Error **errp)
>>>>         return !vfio_block_migration(vbasedev, err, errp);
>>>>     }
>>>>
>>>> -    if (!vbasedev->dirty_pages_supported) {
>>>> +    if (!vbasedev->dirty_pages_supported &&
>>>> +        !vbasedev->bcontainer->dirty_pages_supported) {
>>>>         if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO) {
>>>>             error_setg(&err,
>>>>                        "%s: VFIO device doesn't support device dirty tracking",
>>>
>>> I'm not sure if this message needs to be updated, " VFIO device doesn't support device and IOMMU dirty tracking"
>>>
>>> Same for the below:
>>>
>>> warn_report("%s: VFIO device doesn't support device dirty tracking"
>>
>>
>> Ah yes, good catch. Additionally I think I should check device hwpt rather than
>> container::dirty_pages_supported i.e.
>>
>> if (!vbasedev->dirty_pages_supported &&
>>     (vbasedev->hwpt && !iommufd_hwpt_dirty_tracking(vbasedev->hwpt)))
>>
>> This makes sure that migration is blocked with more accuracy
> 
> I retract this comment as I think it can all be easily detected by not OR-ing
> the setting of vbasedev->bcontainer->dirty_pages_supported. I should put a
> warn_report_once() there.

Something like this below.

To be clear: this is mostly a safe guard against a theoretic case that we don't
know it exists. For example on x86, this is homogeneous and I suspect server ARM
to be the case too. embedded ARM might be different as there's so many
incantations of it.

@@ -267,6 +282,13 @@ static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
     vbasedev->hwpt = hwpt;
     QLIST_INSERT_HEAD(&hwpt->device_list, vbasedev, hwpt_next);
     QLIST_INSERT_HEAD(&container->hwpt_list, hwpt, next);
+
+    if (container->bcontainer.dirty_pages_supported &&
+        !iommufd_hwpt_dirty_tracking(hwpt)) {
+        warn_report("%s: IOMMU dirty tracking not supported\n", vbasedev->name);
+    }
+    container->bcontainer.dirty_pages_supported =
+                              iommufd_hwpt_dirty_tracking(hwpt);
     return true;
 }