Re: [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit

[H. Peter Anvin]

Jeremy Fitzhardinge wrote:
> > No, it's the fact that the 1:1 mapping needs as much virtual space as
> > the physical range covered (including all holes).
>
> Right, I see.  And suddenly 64-bits seems... constrained. ;)

Not really.  The vendors are aware of this constraint -- it's hardly 
unique to Linux.  The reason for canonical addresses and all that jazz 
is to keep people from doing stupid things like store stuff in the upper 
16 bits of a pointer (happened a lot on the 68000, where the first 
implementation had only 24 address bits.)  Thus, all changes needed to 
go to a larger virtual address space are all internal to the kernel.

	-hpa
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