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Re: [Xen-devel] Re: [PATCH 06/16] xen: disable PAT

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH 06/16] xen: disable PAT
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 11 May 2009 11:05:55 -0700
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Jan Beulich wrote:
Depending on what exact plans you have here, I would question whether
having an upper layer dictate mechanisms used by a lower layer. In
particular, just like with the same mistake made with kexec,
- Linux's use of PAT may change (specifically, the value it writes to the PAT
  MSR may not be statically determinable at some point, making the ELF note
  approach you indicated as a possible solution unusable)

If Linux grows the ability to dynamically choose its PAT settings at runtime, then we can hook that mechanism to make sure there's some way to work with Xen. The current problem is because both Linux and Xen current have incompatible static PAT setups.

- the interface may not be suitable for non-Linux

How do other guests use PAT (both native and under Xen)?

   J

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