linux/Documentation/arm64/booting.txt
Linus Torvalds 2dc10ad81f arm64 updates for 4.4:
- "genirq: Introduce generic irq migration for cpu hotunplugged" patch
   merged from tip/irq/for-arm to allow the arm64-specific part to be
   upstreamed via the arm64 tree
 
 - CPU feature detection reworked to cope with heterogeneous systems
   where CPUs may not have exactly the same features. The features
   reported by the kernel via internal data structures or ELF_HWCAP are
   delayed until all the CPUs are up (and before user space starts)
 
 - Support for 16KB pages, with the additional bonus of a 36-bit VA
   space, though the latter only depending on EXPERT
 
 - Implement native {relaxed, acquire, release} atomics for arm64
 
 - New ASID allocation algorithm which avoids IPI on roll-over, together
   with TLB invalidation optimisations (using local vs global where
   feasible)
 
 - KASan support for arm64
 
 - EFI_STUB clean-up and isolation for the kernel proper (required by
   KASan)
 
 - copy_{to,from,in}_user optimisations (sharing the memcpy template)
 
 - perf: moving arm64 to the arm32/64 shared PMU framework
 
 - L1_CACHE_BYTES increased to 128 to accommodate Cavium hardware
 
 - Support for the contiguous PTE hint on kernel mapping (16 consecutive
   entries may be able to use a single TLB entry)
 
 - Generic CONFIG_HZ now used on arm64
 
 - defconfig updates
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Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 updates from Catalin Marinas:

 - "genirq: Introduce generic irq migration for cpu hotunplugged" patch
   merged from tip/irq/for-arm to allow the arm64-specific part to be
   upstreamed via the arm64 tree

 - CPU feature detection reworked to cope with heterogeneous systems
   where CPUs may not have exactly the same features.  The features
   reported by the kernel via internal data structures or ELF_HWCAP are
   delayed until all the CPUs are up (and before user space starts)

 - Support for 16KB pages, with the additional bonus of a 36-bit VA
   space, though the latter only depending on EXPERT

 - Implement native {relaxed, acquire, release} atomics for arm64

 - New ASID allocation algorithm which avoids IPI on roll-over, together
   with TLB invalidation optimisations (using local vs global where
   feasible)

 - KASan support for arm64

 - EFI_STUB clean-up and isolation for the kernel proper (required by
   KASan)

 - copy_{to,from,in}_user optimisations (sharing the memcpy template)

 - perf: moving arm64 to the arm32/64 shared PMU framework

 - L1_CACHE_BYTES increased to 128 to accommodate Cavium hardware

 - Support for the contiguous PTE hint on kernel mapping (16 consecutive
   entries may be able to use a single TLB entry)

 - Generic CONFIG_HZ now used on arm64

 - defconfig updates

* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (91 commits)
  arm64/efi: fix libstub build under CONFIG_MODVERSIONS
  ARM64: Enable multi-core scheduler support by default
  arm64/efi: move arm64 specific stub C code to libstub
  arm64: page-align sections for DEBUG_RODATA
  arm64: Fix build with CONFIG_ZONE_DMA=n
  arm64: Fix compat register mappings
  arm64: Increase the max granular size
  arm64: remove bogus TASK_SIZE_64 check
  arm64: make Timer Interrupt Frequency selectable
  arm64/mm: use PAGE_ALIGNED instead of IS_ALIGNED
  arm64: cachetype: fix definitions of ICACHEF_* flags
  arm64: cpufeature: declare enable_cpu_capabilities as static
  genirq: Make the cpuhotplug migration code less noisy
  arm64: Constify hwcap name string arrays
  arm64/kvm: Make use of the system wide safe values
  arm64/debug: Make use of the system wide safe value
  arm64: Move FP/ASIMD hwcap handling to common code
  arm64/HWCAP: Use system wide safe values
  arm64/capabilities: Make use of system wide safe value
  arm64: Delay cpu feature capability checks
  ...
2015-11-04 14:47:13 -08:00

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Booting AArch64 Linux
=====================
Author: Will Deacon <will.deacon@arm.com>
Date : 07 September 2012
This document is based on the ARM booting document by Russell King and
is relevant to all public releases of the AArch64 Linux kernel.
The AArch64 exception model is made up of a number of exception levels
(EL0 - EL3), with EL0 and EL1 having a secure and a non-secure
counterpart. EL2 is the hypervisor level and exists only in non-secure
mode. EL3 is the highest priority level and exists only in secure mode.
For the purposes of this document, we will use the term `boot loader'
simply to define all software that executes on the CPU(s) before control
is passed to the Linux kernel. This may include secure monitor and
hypervisor code, or it may just be a handful of instructions for
preparing a minimal boot environment.
Essentially, the boot loader should provide (as a minimum) the
following:
1. Setup and initialise the RAM
2. Setup the device tree
3. Decompress the kernel image
4. Call the kernel image
1. Setup and initialise RAM
---------------------------
Requirement: MANDATORY
The boot loader is expected to find and initialise all RAM that the
kernel will use for volatile data storage in the system. It performs
this in a machine dependent manner. (It may use internal algorithms
to automatically locate and size all RAM, or it may use knowledge of
the RAM in the machine, or any other method the boot loader designer
sees fit.)
2. Setup the device tree
-------------------------
Requirement: MANDATORY
The device tree blob (dtb) must be placed on an 8-byte boundary and must
not exceed 2 megabytes in size. Since the dtb will be mapped cacheable
using blocks of up to 2 megabytes in size, it must not be placed within
any 2M region which must be mapped with any specific attributes.
NOTE: versions prior to v4.2 also require that the DTB be placed within
the 512 MB region starting at text_offset bytes below the kernel Image.
3. Decompress the kernel image
------------------------------
Requirement: OPTIONAL
The AArch64 kernel does not currently provide a decompressor and
therefore requires decompression (gzip etc.) to be performed by the boot
loader if a compressed Image target (e.g. Image.gz) is used. For
bootloaders that do not implement this requirement, the uncompressed
Image target is available instead.
4. Call the kernel image
------------------------
Requirement: MANDATORY
The decompressed kernel image contains a 64-byte header as follows:
u32 code0; /* Executable code */
u32 code1; /* Executable code */
u64 text_offset; /* Image load offset, little endian */
u64 image_size; /* Effective Image size, little endian */
u64 flags; /* kernel flags, little endian */
u64 res2 = 0; /* reserved */
u64 res3 = 0; /* reserved */
u64 res4 = 0; /* reserved */
u32 magic = 0x644d5241; /* Magic number, little endian, "ARM\x64" */
u32 res5; /* reserved (used for PE COFF offset) */
Header notes:
- As of v3.17, all fields are little endian unless stated otherwise.
- code0/code1 are responsible for branching to stext.
- when booting through EFI, code0/code1 are initially skipped.
res5 is an offset to the PE header and the PE header has the EFI
entry point (efi_stub_entry). When the stub has done its work, it
jumps to code0 to resume the normal boot process.
- Prior to v3.17, the endianness of text_offset was not specified. In
these cases image_size is zero and text_offset is 0x80000 in the
endianness of the kernel. Where image_size is non-zero image_size is
little-endian and must be respected. Where image_size is zero,
text_offset can be assumed to be 0x80000.
- The flags field (introduced in v3.17) is a little-endian 64-bit field
composed as follows:
Bit 0: Kernel endianness. 1 if BE, 0 if LE.
Bit 1-2: Kernel Page size.
0 - Unspecified.
1 - 4K
2 - 16K
3 - 64K
Bits 3-63: Reserved.
- When image_size is zero, a bootloader should attempt to keep as much
memory as possible free for use by the kernel immediately after the
end of the kernel image. The amount of space required will vary
depending on selected features, and is effectively unbound.
The Image must be placed text_offset bytes from a 2MB aligned base
address near the start of usable system RAM and called there. Memory
below that base address is currently unusable by Linux, and therefore it
is strongly recommended that this location is the start of system RAM.
The region between the 2 MB aligned base address and the start of the
image has no special significance to the kernel, and may be used for
other purposes.
At least image_size bytes from the start of the image must be free for
use by the kernel.
Any memory described to the kernel (even that below the start of the
image) which is not marked as reserved from the kernel (e.g., with a
memreserve region in the device tree) will be considered as available to
the kernel.
Before jumping into the kernel, the following conditions must be met:
- Quiesce all DMA capable devices so that memory does not get
corrupted by bogus network packets or disk data. This will save
you many hours of debug.
- Primary CPU general-purpose register settings
x0 = physical address of device tree blob (dtb) in system RAM.
x1 = 0 (reserved for future use)
x2 = 0 (reserved for future use)
x3 = 0 (reserved for future use)
- CPU mode
All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
IRQ and FIQ).
The CPU must be in either EL2 (RECOMMENDED in order to have access to
the virtualisation extensions) or non-secure EL1.
- Caches, MMUs
The MMU must be off.
Instruction cache may be on or off.
The address range corresponding to the loaded kernel image must be
cleaned to the PoC. In the presence of a system cache or other
coherent masters with caches enabled, this will typically require
cache maintenance by VA rather than set/way operations.
System caches which respect the architected cache maintenance by VA
operations must be configured and may be enabled.
System caches which do not respect architected cache maintenance by VA
operations (not recommended) must be configured and disabled.
- Architected timers
CNTFRQ must be programmed with the timer frequency and CNTVOFF must
be programmed with a consistent value on all CPUs. If entering the
kernel at EL1, CNTHCTL_EL2 must have EL1PCTEN (bit 0) set where
available.
- Coherency
All CPUs to be booted by the kernel must be part of the same coherency
domain on entry to the kernel. This may require IMPLEMENTATION DEFINED
initialisation to enable the receiving of maintenance operations on
each CPU.
- System registers
All writable architected system registers at the exception level where
the kernel image will be entered must be initialised by software at a
higher exception level to prevent execution in an UNKNOWN state.
For systems with a GICv3 interrupt controller to be used in v3 mode:
- If EL3 is present:
ICC_SRE_EL3.Enable (bit 3) must be initialiased to 0b1.
ICC_SRE_EL3.SRE (bit 0) must be initialised to 0b1.
- If the kernel is entered at EL1:
ICC.SRE_EL2.Enable (bit 3) must be initialised to 0b1
ICC_SRE_EL2.SRE (bit 0) must be initialised to 0b1.
- The DT or ACPI tables must describe a GICv3 interrupt controller.
For systems with a GICv3 interrupt controller to be used in
compatibility (v2) mode:
- If EL3 is present:
ICC_SRE_EL3.SRE (bit 0) must be initialised to 0b0.
- If the kernel is entered at EL1:
ICC_SRE_EL2.SRE (bit 0) must be initialised to 0b0.
- The DT or ACPI tables must describe a GICv2 interrupt controller.
The requirements described above for CPU mode, caches, MMUs, architected
timers, coherency and system registers apply to all CPUs. All CPUs must
enter the kernel in the same exception level.
The boot loader is expected to enter the kernel on each CPU in the
following manner:
- The primary CPU must jump directly to the first instruction of the
kernel image. The device tree blob passed by this CPU must contain
an 'enable-method' property for each cpu node. The supported
enable-methods are described below.
It is expected that the bootloader will generate these device tree
properties and insert them into the blob prior to kernel entry.
- CPUs with a "spin-table" enable-method must have a 'cpu-release-addr'
property in their cpu node. This property identifies a
naturally-aligned 64-bit zero-initalised memory location.
These CPUs should spin outside of the kernel in a reserved area of
memory (communicated to the kernel by a /memreserve/ region in the
device tree) polling their cpu-release-addr location, which must be
contained in the reserved region. A wfe instruction may be inserted
to reduce the overhead of the busy-loop and a sev will be issued by
the primary CPU. When a read of the location pointed to by the
cpu-release-addr returns a non-zero value, the CPU must jump to this
value. The value will be written as a single 64-bit little-endian
value, so CPUs must convert the read value to their native endianness
before jumping to it.
- CPUs with a "psci" enable method should remain outside of
the kernel (i.e. outside of the regions of memory described to the
kernel in the memory node, or in a reserved area of memory described
to the kernel by a /memreserve/ region in the device tree). The
kernel will issue CPU_ON calls as described in ARM document number ARM
DEN 0022A ("Power State Coordination Interface System Software on ARM
processors") to bring CPUs into the kernel.
The device tree should contain a 'psci' node, as described in
Documentation/devicetree/bindings/arm/psci.txt.
- Secondary CPU general-purpose register settings
x0 = 0 (reserved for future use)
x1 = 0 (reserved for future use)
x2 = 0 (reserved for future use)
x3 = 0 (reserved for future use)