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[Xen-devel] Re: sysenter/syscall support for 32-on-64 guests?

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: [Xen-devel] Re: sysenter/syscall support for 32-on-64 guests?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 28 Feb 2008 12:19:25 -0800
Cc: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <ijc@xxxxxxxxxxxxxx>
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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.)


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