From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: sysenter/syscall support for 32-on-64 guests?
Date: Thu, 28 Feb 2008 12:19:25 -0800
Message-ID: <47C7174D.3070102@goop.org>
References: <47C6E634.3080609@goop.org> <47C6F9FD.76E4.0078.0@novell.com>
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To: Jan Beulich <jbeulich@novell.com>
Cc: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>, Xen-devel <xen-devel@lists.xensource.com>, Ian Campbell <ijc@hellion.org.uk>
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Jan Beulich wrote:
> Since int80 cannot be directly passed to the guest (as in 32-on-32), it
> seemed reasonable to cut on the overhead of syscalls by at least
> allowing this (and syscall could also be made work now that the vdso
> stuff is unified in 2.6.25) - for obvious reasons it still goes through the
> hypervisor, but gets there faster
>   

I guess that's a reasonable point.  But it does mean that you'd need to 
separately validate a 32-bit guest on both a 32 and 64-bit hypervisor, 
which is a bit painful.  Maybe you'd need to do that anyway... (Or 
ignore 32-bit hosts.)

    J