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

H. Peter Anvin
2010-10-13T23:08:20Z

On 10/13/2010 04:02 PM, Jeremy Fitzhardinge wrote:
>
> This seems to do the trick:
>
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.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@citrix.com>
>

Seems both clean and The Right Thing[TM].

-hpa