linux-kernel - Re: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory

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Message-ID: <18878791-c24a-4ca7-aa19-904805bc1314@email.android.com>
Date:	Tue, 21 Jun 2011 11:02:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>
Subject: Re: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping

Stefano Stabellini <stefano.stabellini@...citrix.com> wrote:

>On Mon, 20 Jun 2011, H. Peter Anvin wrote:
>> On 06/07/2011 11:13 AM, stefano.stabellini@...citrix.com 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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