From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch 14/21] Xen-paravirt: Add XEN config options and
	disableunsupported config options.
Date: Fri, 16 Feb 2007 02:54:52 -0800
Message-ID: <20070216025452.d25e3545.akpm@linux-foundation.org>
References: <20070216020947.03e1726e.akpm@linux-foundation.org>
	<C1FB3C2F.98E9%keir@xensource.com>
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To: Keir Fraser <keir@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>, Andi Kleen <ak@muc.de>, xen-devel@lists.xensource.com, Ian Pratt <Ian.Pratt@xensource.com>, virtualization@lists.osdl.org, Steven Hand <steven.hand@cl.cam.ac.uk>, Christian Limpach <Christian.Limpach@xensource.com>, linux-kernel@vger.kernel.org
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On Fri, 16 Feb 2007 10:47:11 +0000 Keir Fraser <keir@xensource.com> wrote:

> On 16/2/07 10:09, "Andrew Morton" <akpm@linux-foundation.org> wrote:
> =

> > Are the places where the domU code references machine addresses splatte=
red
> > all over the code?  If not, they can just be wrapped with
> > preempt_disable/preempt_enable?
> =

> The main places where machine addresses are 'visible' are any code that
> holds a pte_t,pmd_t,pud_t,pgd_t. We hide the machine-to-pseudophysical and
> pseudophysical-to-machine translations inside e.g., pte_val() and __pte()
> (i.e., constructors and extractors for page table entries). Obviously the
> users of these macros are open coded all over the place, quite apart from
> the performance cost of sprinkling preempt_{enable,disable} so liberally.

OK, you're screwed.  I agree that the process freezer is the way out of tha=
t one.

Ingo said that he's clocked the freezer at a few milliseconds.  But if it's
any higher than that it'll need to get sped up once we convert cpu hotplug
to use it.