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    SubjectRe: [PATCH 1/3] x86: calculate precisely the memory needed by init_memory_mapping
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    Stefano Stabellini <stefano.stabellini@eu.citrix.com> wrote:

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