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Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through dev
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [Qemu-devel] hotplug: VM got stuck when attaching a pass-through device to the non-pass-through VM for the first time |
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Date: |
Tue, 18 Feb 2014 12:51:59 +0200 |
On Tue, Feb 18, 2014 at 11:42:19AM +0100, Paolo Bonzini wrote:
> Il 18/02/2014 11:38, Michael S. Tsirkin ha scritto:
> >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.
>
> Paolo
Or the new shared flag - IIRC shared VMAs don't do COW either.