Messages in this thread |  | | | Date | Thu, 05 Jun 2008 09:45:58 -0700 | | From | "H. Peter Anvin" <> | | Subject | Re: [PATCH] x86: set PAE PHYSICAL_MASK_SHIFT to match 64-bit |
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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
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