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

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: [Xen-devel] sysenter/syscall support for 32-on-64 guests?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 28 Feb 2008 08:49:56 -0800
Cc: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <ijc@xxxxxxxxxxxxxx>
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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.


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