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xen-devel
[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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Tue, 21 Jun 2011 11:23:35 -0700 |
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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
>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.
--
Sent from my mobile phone. Please excuse my brevity and lack of formatting.
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