From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: sysenter/syscall support for 32-on-64 guests?
Date: Thu, 28 Feb 2008 08:49:56 -0800
Message-ID: <47C6E634.3080609@goop.org>
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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>
List-Id: xen-devel@lists.xenproject.org

I just spent quite a while working out why pvops-Xen kernels weren't 
booting for me in a 64-bit hypervisor.  It turned out to be because 
32-on-64 supports SEP even though 32-on-32 doesn't, so the guest kernel 
was trying to use it without having set up the Xen side, resulting in 
syscalls jumping to 0:0, generating a mysterious GP.  Once I worked that 
out, the fix was simple, of course.

Anyway, I wonder if you had a specific reason for allowing this, other 
than "because we can"?  It seems to me that we should try to minimize 
the number of differences between 32-on-32 and 32-on-64 as much as possible.

    J