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Re: [Xen-devel] [PATCH 6/7, RFC] x86_64: basic changes for supporting co

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 6/7, RFC] x86_64: basic changes for supporting compatibility mode guest
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Wed, 23 Aug 2006 12:32:12 +0200
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There was one more issue I forgot to mention: We must disable execution of
'syscall' in some way for compatibility domains. The question is whether to
add respective detection code early into the syscall path (which would affect
performance-wise all 64-bit domains) or whether to {dis,en}able the use of
the instruction in the context switch code by updating EFER as needed
(which would have a performance effect only when switching between
a native and a compatibility domain, but the performance effect would likely
be significantly greater). I'd prefer the second option, not the least because
its implementation is significantly easier.

Jan

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