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Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options a

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options.
From: Zachary Amsden <zach@xxxxxxxxxx>
Date: Tue, 13 Feb 2007 15:58:20 -0800
Cc: Andrew Morton <akpm@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, Dan Hecht <dhecht@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx
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Jeremy Fitzhardinge wrote:
Dan Hecht wrote:
I assume you plan to eventually get all this stuff working but just
want to prevent configurations that the Xen paravirt-ops isn't ready
for at the moment?

Instead can you do it this way:

config XEN
    depends on PARAVIRT && !PREEMPT && HZ_100 && !DOUBLEFAULT && !KEXEC

That's a bit simpler code-wise, but it does make it pretty complex to
get everything just-so to even see the CONFIG_XEN option.

Yes, but that is what you need to do to compile Xen - logically, to build a Xen kernel, you need to have a kernel configuration which can enable Xen - not limit the configuration of a kernel because Xen has been enabled. This is because with paravirt-ops, Xen compiled kernels may not actually run on Xen, so you can't arbitrarily drop features because you assume Xen is there.

One of these has an easy solution - doublefault. You don't need to install the doublefault gate if you don't want it, and the hypervisor doesn't need to freak out if you install it, it can just ignore the gate entirely and claim #DF is not supported.

Zach

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