linux-kernel - Re: [PATCH 0/4] memblock related fixes for -tip

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Date:	Wed, 13 Oct 2010 16:07:46 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 0/4] memblock related fixes for -tip

On 10/13/2010 04:02 PM, Jeremy Fitzhardinge wrote:
> 
> This seems to do the trick:
> 
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Date: Wed, 13 Oct 2010 14:21:55 -0700
> Subject: [PATCH] xen: cope with unmapped pages when initializing kernel pagetable
> 
> Xen requires that all pages containing pagetable entries to be mapped
> read-only.  If pages used for the initial pagetable are already mapped
> then we can change the mapping to RO.  However, if they are initially
> unmapped, we need to make sure that when they are later mapped, they
> are also mapped RO.
> 
> We do this by knowing that the kernel pagetable memory is pre-allocated
> in the range e820_table_start - e820_table_end, so any pfn within this
> range should be mapped read-only.  However, the pagetable setup code
> early_ioremaps the pages to write their entries, so we must make sure
> that mappings created in the early_ioremap fixmap area are mapped RW.
> (Those mappings are removed before the pages are presented to Xen
> as pagetable pages.)
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 

Seems both clean and The Right Thing[TM].

	-hpa
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