Re: [Xen-devel] x86-64's contig_initmem_init

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>The tail part of the initial mapping has no special handling on i386 
>nor on x86_64. It just gets freed up when we free from 0 up to
max_pfn, 
>and it never gets reserved (the reserved region precisely covers
kernel 
>text/data and initial page tables).

For i386 I'm not certain, but for x86-64 I doubt that:
init_memory_mapping, which runs before contig_initmem_init,
re-initializes start_pfn (which is what in turn gets used to set up the
bootmem reservation) from the result of scanning the initial page
tables. These, as I understand it, extend to the 4-Mb-rounded end of the
initial mapping (which, if the unused tail turns out to be less than
512k, even gets extended by an extra 4M).

>Actually, that could be another bug on x86/64 -- I may need to
truncate 
>the initial mapping, or we may be ending up with spurious extra 
>writable mappings to some pages... I'll take a look and see if this is

>the case.

If the above wasn't true (or was fixed), then I'd assume such a bug
would surface (and again I'm not sure why i386 wouldn't surface it, as I
can't see where these mappings get torn down).

Jan

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