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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 30 Aug 2005, at 14:53, Jan Beulich wrote:

> Hmm, interesting. If that change was done along with the one to
> contig_initmem_init, it would have saved me well over a day of
> debugging...
It needed to be debugged here too. I can't foresee all bugs 
unfortunately. :-)
> Anyway, I can't see where the respective freeing is done on i386, and I
> still can't see how the tail part of the initial mapping is being made
> use of on either 32- or 64bits.
For i386, it is freed to the bootmem allocator in 
register_bootmem_low_pages(), which walks a fake e820 table that is 
created by machine_specific_memory_setup() in 
include/asm-xen/asm-i386/mach-xen/setup_arch_post.h.
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).
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.
 -- Keir


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