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

H. Peter Anvin
2008-06-07T18:43:08Z

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