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Subject: Re: [Qemu-devel] Merging improvements from VirtualBox OSE into qemu?
References: <49522F8D.4000203@turnkeylinux.org>	<200812241336.01702.paul@codesourcery.com>
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To: qemu-devel@nongnu.org
Cc: turnkey-discuss@lists.turnkeylinux.org, Paul Brook <paul@codesourcery.com>

Liraz Siri wrote:
> I don't really understand the implementation VirtualBox uses to
> accomplish running 64bit VM guests on a 32bit host. Is it possible
> VirtualBox have figured out how to run 64bit instructions on a host
> running in 32bit mode? (otherwise they'll need to be doing some kind of
> emulation)
>
>   

There's nothing magical about it.  Most likely they switch to 64-bit 
mode immediately before entering the guest, and switch back immediately 
after the guest exits.  In effect their turning the host OS into a 
hybrid 32/64 bit kernel (with the vast majority of the code remaining 
32-bits).


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.