From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <jbeulich@novell.com>
Subject: Re: [PATCH, fixed] linux/x86: use sysenter/syscall
	for 32-bit apps on 64-bit Xen
Date: Wed, 24 Oct 2007 15:15:41 +0100
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To: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
Cc: xen-devel@lists.xensource.com, Andi Kleen <ak@suse.de>
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>>However, in case (2) the i386 guest kernel unconditionally goes for
>>sysenter, and the hypervisor will accept this because CPUID has =
advertised
>>SEP. *But* AMD CPUs do not support sysenter except in legacy mode! The
>>correct thing to do is to use syscall. The hypervisor 32-on-64 compat =
code
>>would accept CALLBACKTYPE_syscall, but the Linux i386 code here doesn't
>>appear to make use of it. So I would imagine that the i386 kernel =
running on
>>AMD hardware would cause all user processes to crash when they SYSENTER.
>
>I intentionally avoided adding syscall stuff to the 32-bit kernel, since =
that isn't
>there in the native kernel either (as it's not really usable on native). =
Therefore
>I'd suggest clearing SEP for pv32-on-64 guests in emulate_forced_invalid_o=
p()

... on AMD CPUs I meant to say.

Jan