Messages in this thread | | | Date | Tue, 04 Oct 2005 20:59:48 +0900 | From | Tejun Heo <> | Subject | Question regarding x86_64 __PHYSICAL_MASK_SHIFT |
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Hello, Andi.
In include/asm-x86_64/page.h, __VIRTUAL_MASK_SHIFT is defined as 48 bits which is the size of virtual address space on current x86_64 machines as used as such. OTOH, __PHYSICAL_MASK_SHIFT is defined as 46 and used as mask shift for physical page address (i.e. physaddr >> 12).
In addition to being a bit confusing due to similar names but different meanings, this means that we assume processors can physically address 58 (46 + 12) bits, but both amd64 and IA-32e manuals say that current architectural limit is 52 bits and bits 52-62 are reserved in all page table entries. This currently (and in foreseeable future) doesn't cause any problem but it's still a bit weird.
Am I missing something?
Thanks.
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