Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time

[Zhanghaoyu (A)]

>> What if you detach and re-attach?
>> Is it fast then?
>> If yes this means the issue is COW breaking that occurs with 
>> get_user_pages, not translation as such.
>> Try hugepages with prealloc - does it help?
>
>I agree it's either COW breaking or (similarly) locking pages that the guest 
>hasn't touched yet.
>
>You can use prealloc or "-rt mlock=on" to avoid this problem.
>
It gets better if using "-rt mlock=on", but still cannot resolve the problem 
completely.
VT-d and EPT do not share the GPA->HPA page-table, still need to build VT-d 
GPA->HPA DMAR page-table,
Although the "-rt mlock=on" option guarantees that all of vm memory have been 
touched before attaching 
the pass-through device, the building is faster, but which still need some time.

Thanks,
Zhang Haoyu

>Paolo