About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / x86 / x86_64 / mm.txt




Custom Search

Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.

1	
2	<previous description obsolete, deleted>
3	
4	Virtual memory map with 4 level page tables:
5	
6	0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
7	hole caused by [48:63] sign extension
8	ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
9	ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
10	ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
11	ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
12	ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
13	ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
14	... unused hole ...
15	ffffec0000000000 - fffffc0000000000 (=44 bits) kasan shadow memory (16TB)
16	... unused hole ...
17	ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
18	... unused hole ...
19	ffffffef00000000 - ffffffff00000000 (=64 GB) EFI region mapping space
20	... unused hole ...
21	ffffffff80000000 - ffffffffa0000000 (=512 MB)  kernel text mapping, from phys 0
22	ffffffffa0000000 - ffffffffff5fffff (=1526 MB) module mapping space
23	ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
24	ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
25	
26	The direct mapping covers all memory in the system up to the highest
27	memory address (this means in some cases it can also include PCI memory
28	holes).
29	
30	vmalloc space is lazily synchronized into the different PML4 pages of
31	the processes using the page fault handler, with init_level4_pgt as
32	reference.
33	
34	Current X86-64 implementations support up to 46 bits of address space (64 TB),
35	which is our current limit. This expands into MBZ space in the page tables.
36	
37	We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual
38	memory window (this size is arbitrary, it can be raised later if needed).
39	The mappings are not part of any other kernel PGD and are only available
40	during EFI runtime calls.
41	
42	Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
43	physical memory, vmalloc/ioremap space and virtual memory map are randomized.
44	Their order is preserved but their base will be offset early at boot time.
45	
46	-Andi Kleen, Jul 2004
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.