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Subject[patch V181 10/54] x86/doc: Remove obvious weirdness
From: Peter Zijlstra <>

Signed-off-by: Peter Zijlstra (Intel) <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Thomas Gleixner <>
Cc: Andy Lutomirski <>
Cc: Boris Ostrovsky <>
Cc: Borislav Petkov <>
Cc: Brian Gerst <>
Cc: Dave Hansen <>
Cc: David Laight <>
Cc: Denys Vlasenko <>
Cc: Eduardo Valentin <>
Cc: Greg KH <>
Cc: H. Peter Anvin <>
Cc: Josh Poimboeuf <>
Cc: Juergen Gross <>
Cc: Linus Torvalds <>
Cc: Will Deacon <>
Documentation/x86/x86_64/mm.txt | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)

--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -1,6 +1,4 @@

-<previous description obsolete, deleted>
Virtual memory map with 4 level page tables:

0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
@@ -49,8 +47,9 @@ ffffffffffe00000 - ffffffffffffffff (=2

Architecture defines a 64-bit virtual address. Implementations can support
less. Currently supported are 48- and 57-bit virtual addresses. Bits 63
-through to the most-significant implemented bit are set to either all ones
-or all zero. This causes hole between user space and kernel addresses.
+through to the most-significant implemented bit are sign extended.
+This causes hole between user space and kernel addresses if you interpret them
+as unsigned.

The direct mapping covers all memory in the system up to the highest
memory address (this means in some cases it can also include PCI memory
@@ -60,9 +59,6 @@ vmalloc space is lazily synchronized int
the processes using the page fault handler, with init_top_pgt as

-Current X86-64 implementations support up to 46 bits of address space (64 TB),
-which is our current limit. This expands into MBZ space in the page tables.
We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual
memory window (this size is arbitrary, it can be raised later if needed).
The mappings are not part of any other kernel PGD and are only available
@@ -74,5 +70,3 @@ following fixmap section.
Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
physical memory, vmalloc/ioremap space and virtual memory map are randomized.
Their order is preserved but their base will be offset early at boot time.
--Andi Kleen, Jul 2004

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