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[Xen-devel] Re: [PATCH 1/3] x86: calculate precisely the memory needed b

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Tue, 21 Jun 2011 11:02:43 -0700
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "mingo@xxxxxxx" <mingo@xxxxxxx>, "yinghai@xxxxxxxxxx" <yinghai@xxxxxxxxxx>
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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
>> > needed: the PMD entry is already allocated and contiguous for the
>> > range (a PMD page covers 4G of virtual addresses) and the pte entry
>> > already allocated by early_ioremap_init.
>> > 
>> Hi Stefano,
>> I think this is wrong.  A PMD page covers *1G* of virtual addresses,
>> 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
>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

Ok, wasn't sure if Xen used the static allocation or not.
Sent from my mobile phone. Please excuse my brevity and lack of formatting.

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