forked from luck/tmp_suning_uos_patched
1eb7756902
commit 7a1be318f5795cb66fa0dc86b3ace427fe68057f upstream On ARM, setting up the linear region is tricky, given the constraints around placement and alignment of the memblocks, and how the kernel itself as well as the DT are placed in physical memory. Let's simplify matters a bit, by moving the device tree mapping to the top of the address space, right between the end of the vmalloc region and the start of the the fixmap region, and create a read-only mapping for it that is independent of the size of the linear region, and how it is organized. Since this region was formerly used as a guard region, which will now be populated fully on LPAE builds by this read-only mapping (which will still be able to function as a guard region for stray writes), bump the start of the [underutilized] fixmap region by 512 KB as well, to ensure that there is always a proper guard region here. Doing so still leaves ample room for the fixmap space, even with NR_CPUS set to its maximum value of 32. Tested-by: Linus Walleij <linus.walleij@linaro.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Reviewed-by: Nicolas Pitre <nico@fluxnic.net> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
99 lines
3.5 KiB
ReStructuredText
99 lines
3.5 KiB
ReStructuredText
=================================
|
|
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.
|
|
|
|
ffc80000 ffefffff Fixmap mapping region. Addresses provided
|
|
by fix_to_virt() will be located here.
|
|
|
|
ffc00000 ffc7ffff Guard region
|
|
|
|
ff800000 ffbfffff Permanent, fixed read-only mapping of the
|
|
firmware provided DT blob
|
|
|
|
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().
|