Re: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping

[H. Peter Anvin]

Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:

>On Mon, 20 Jun 2011, H. Peter Anvin wrote:
>> On 06/07/2011 11:13 AM, stefano.stabellini@xxxxxxxxxxxxx wrote:
>> > 
>> > - remove the extra page added on x86_32 for the fixmap because is
>not
>> > needed: the PMD entry is already allocated and contiguous for the
>whole
>> > range (a PMD page covers 4G of virtual addresses) and the pte entry
>is
>> > already allocated by early_ioremap_init.
>> > 
>> 
>> Hi Stefano,
>> 
>> I think this is wrong.  A PMD page covers *1G* of virtual addresses,
>and
>> in the 2+2 and 1+3 memory configurations, we may or may not need a
>> separate PMD for the fixmap.
>> 
>> Am I missing something?
>
>You are right, a PMD page covers 1G of virtual addresses so that part
>of
>the explanation in the comment is wrong.
>
>The reason why we don't need a separate PMD for the fixmap is that in
>both PAE and non-PAE cases the last gigabyte of virtual addresses is
>always covered by the initial allocation in head_32.S (swapper_pg_dir
>or
>initial_pg_pmd).

Ok, wasn't sure if Xen used the static allocation or not.
-- 
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