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authorPeter Zijlstra <peterz@infradead.org>2017-12-05 13:34:54 +0100
committerIngo Molnar <mingo@kernel.org>2017-12-22 20:13:02 +0100
commite8ffe96e5933d417195268478479933d56213a3f (patch)
tree2f9e031295f56b1f963469f01d6e1299319b3380 /Documentation/x86
parent5a7ccf4754fb3660569a6de52ba7f7fc3dfaf280 (diff)
downloadlinux-e8ffe96e5933d417195268478479933d56213a3f.tar.bz2
x86/doc: Remove obvious weirdnesses from the x86 MM layout documentation
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Laight <David.Laight@aculab.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Eduardo Valentin <eduval@amazon.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: linux-mm@kvack.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/x86')
-rw-r--r--Documentation/x86/x86_64/mm.txt12
1 files changed, 3 insertions, 9 deletions
diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index 83ca5a3b90ac..63a41671d25b 100644
--- 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 MB) unused hole
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 into the different PML4/PML5 pages of
the processes using the page fault handler, with init_top_pgt as
reference.
-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