mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-29 07:34:06 +08:00
6ff0966052
There is a 12MB unused region in our memory map between the vmalloc and fixmap areas. This became unused with commite9da6e9905, confirmed with commit64d3b6a3f4. We also have a 8MB guard area before the vmalloc area. With the default 240MB vmalloc area size and the current VMALLOC_END definition, that means the end of low memory ends up at 0xef800000 which is unfortunate for 768MB machines where 8MB of RAM is lost to himem. Let's move VMALLOC_END to 0xff800000 so the guard area won't chop the top of the 768MB low memory area while keeping the default vmalloc area size unchanged and still preserving a gap between the vmalloc and fixmap areas. Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
89 lines
3.1 KiB
Plaintext
89 lines
3.1 KiB
Plaintext
Kernel Memory Layout on ARM Linux
|
|
|
|
Russell King <rmk@arm.linux.org.uk>
|
|
November 17, 2005 (2.6.15)
|
|
|
|
This document describes the virtual memory layout which the Linux
|
|
kernel uses for ARM processors. It indicates which regions are
|
|
free for platforms to use, and which are used by generic code.
|
|
|
|
The ARM CPU is capable of addressing a maximum of 4GB virtual memory
|
|
space, and this must be shared between user space processes, the
|
|
kernel, and hardware devices.
|
|
|
|
As the ARM architecture matures, it becomes necessary to reserve
|
|
certain regions of VM space for use for new facilities; therefore
|
|
this document may reserve more VM space over time.
|
|
|
|
Start End Use
|
|
--------------------------------------------------------------------------
|
|
ffff8000 ffffffff copy_user_page / clear_user_page use.
|
|
For SA11xx and Xscale, this is used to
|
|
setup a minicache mapping.
|
|
|
|
ffff4000 ffffffff cache aliasing on ARMv6 and later CPUs.
|
|
|
|
ffff1000 ffff7fff Reserved.
|
|
Platforms must not use this address range.
|
|
|
|
ffff0000 ffff0fff CPU vector page.
|
|
The CPU vectors are mapped here if the
|
|
CPU supports vector relocation (control
|
|
register V bit.)
|
|
|
|
fffe0000 fffeffff XScale cache flush area. This is used
|
|
in proc-xscale.S to flush the whole data
|
|
cache. (XScale does not have TCM.)
|
|
|
|
fffe8000 fffeffff DTCM mapping area for platforms with
|
|
DTCM mounted inside the CPU.
|
|
|
|
fffe0000 fffe7fff ITCM mapping area for platforms with
|
|
ITCM mounted inside the CPU.
|
|
|
|
ffc00000 ffefffff Fixmap mapping region. Addresses provided
|
|
by fix_to_virt() will be located here.
|
|
|
|
fee00000 feffffff Mapping of PCI I/O space. This is a static
|
|
mapping within the vmalloc space.
|
|
|
|
VMALLOC_START VMALLOC_END-1 vmalloc() / ioremap() space.
|
|
Memory returned by vmalloc/ioremap will
|
|
be dynamically placed in this region.
|
|
Machine specific static mappings are also
|
|
located here through iotable_init().
|
|
VMALLOC_START is based upon the value
|
|
of the high_memory variable, and VMALLOC_END
|
|
is equal to 0xff800000.
|
|
|
|
PAGE_OFFSET high_memory-1 Kernel direct-mapped RAM region.
|
|
This maps the platforms RAM, and typically
|
|
maps all platform RAM in a 1:1 relationship.
|
|
|
|
PKMAP_BASE PAGE_OFFSET-1 Permanent kernel mappings
|
|
One way of mapping HIGHMEM pages into kernel
|
|
space.
|
|
|
|
MODULES_VADDR MODULES_END-1 Kernel module space
|
|
Kernel modules inserted via insmod are
|
|
placed here using dynamic mappings.
|
|
|
|
00001000 TASK_SIZE-1 User space mappings
|
|
Per-thread mappings are placed here via
|
|
the mmap() system call.
|
|
|
|
00000000 00000fff CPU vector page / null pointer trap
|
|
CPUs which do not support vector remapping
|
|
place their vector page here. NULL pointer
|
|
dereferences by both the kernel and user
|
|
space are also caught via this mapping.
|
|
|
|
Please note that mappings which collide with the above areas may result
|
|
in a non-bootable kernel, or may cause the kernel to (eventually) panic
|
|
at run time.
|
|
|
|
Since future CPUs may impact the kernel mapping layout, user programs
|
|
must not access any memory which is not mapped inside their 0x0001000
|
|
to TASK_SIZE address range. If they wish to access these areas, they
|
|
must set up their own mappings using open() and mmap().
|