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xen-devel
[Xen-devel] Re: [PATCH 1/3] x86: calculate precisely the memory needed b
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To: |
"H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping |
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From: |
Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> |
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Date: |
Tue, 21 Jun 2011 18:57:01 +0100 |
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Cc: |
"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx>, "mingo@xxxxxxx" <mingo@xxxxxxx>, "yinghai@xxxxxxxxxx" <yinghai@xxxxxxxxxx> |
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Tue, 21 Jun 2011 10:53:58 -0700 |
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<alpine.DEB.2.00.1106071849290.12963@kaball-desktop> <1307470409-7654-1-git-send-email-stefano.stabellini@xxxxxxxxxxxxx> <4DFFCBAD.9040507@xxxxxxxxxxxxxxx> |
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Alpine 2.00 (DEB 1167 2008-08-23) |
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).
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