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

H. Peter Anvin
2008-06-05T17:02:28Z

Jeremy Fitzhardinge wrote:
>
> We could have an auction:
>
> Do I hear 46? 47? 48? 50? 52! Going once, twice, 52 bits!
>
> Anyway, we can fix it later in a separate patch. This is a
> change-as-little-as-possible bugfix patch.
>

It should either be 52 bits or dynamic based on CPUID information. The
latter is very expensive.

If there end up being additional control bits assigned in this space we
won't use them since we know the size of the address space (which won't
include the control bits) and thus will leave them at zero.

It's largely theoretical, since I believe Linux on x86-64 relies on
virtual >= physical+N, where I believe N is about 3 bits, and the page
table format or page size need to change to support more than 48 bits of
virtual address space.

-hpa