Linux preempt-rt

Check our new training course

Real-Time Linux with PREEMPT_RT

Check our new training course
with Creative Commons CC-BY-SA
lecture and lab materials

Bootlin logo

Elixir Cross Referencer

# Memory Protection Unit (MPU) configuration options

# Copyright (c) 2017 Linaro Limited
# SPDX-License-Identifier: Apache-2.0

if CPU_HAS_MPU

config ARM_MPU
	bool "ARM MPU Support"
	select MPU
	select SRAM_REGION_PERMISSIONS
	select THREAD_STACK_INFO
	select ARCH_HAS_EXECUTABLE_PAGE_BIT
	select MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT if !(CPU_HAS_NXP_MPU || ARMV8_M_BASELINE || ARMV8_M_MAINLINE)
	select MPU_REQUIRES_NON_OVERLAPPING_REGIONS if CPU_HAS_ARM_MPU && (ARMV8_M_BASELINE || ARMV8_M_MAINLINE)
	help
	  MCU implements Memory Protection Unit.

	  Notes:
	  The ARMv6-M and ARMv7-M MPU architecture requires a power-of-two
	  alignment of MPU region base address and size.

	  The NXP MPU as well as the ARMv8-M MPU do not require MPU regions
	  to have power-of-two alignment for base address and region size.

	  The ARMv8-M MPU requires the active MPU regions be non-overlapping.
	  As a result of this, the ARMv8-M MPU needs to fully partition the
	  memory map when programming dynamic memory regions (e.g. PRIV stack
	  guard, user thread stack, and application memory domains), if the
	  system requires PRIV access policy different from the access policy
	  of the ARMv8-M background memory map. The application developer may
	  enforce full PRIV (kernel) memory partition by enabling the
	  CONFIG_MPU_GAP_FILLING option.
	  By not enforcing full partition, MPU may leave part of kernel
	  SRAM area covered only by the default ARMv8-M memory map. This
	  is fine for User Mode, since the background ARM map does not
	  allow nPRIV access at all. However, since the background map
	  policy allows instruction fetches by privileged code, forcing
	  this Kconfig option off prevents the system from directly
	  triggering MemManage exceptions upon accidental attempts to
	  execute code from SRAM in XIP builds.
	  Since this does not compromise User Mode, we make the skipping
	  of full partitioning the default behavior for the ARMv8-M MPU
	  driver.

config ARM_MPU_REGION_MIN_ALIGN_AND_SIZE
	int
	default 256 if ARM_MPU && ARMV6_M_ARMV8_M_BASELINE && !ARMV8_M_BASELINE
	default 32 if ARM_MPU
	default 4
	help
	  Minimum size (and alignment) of an ARM MPU region. Use this
	  symbol to guarantee minimum size and alignment of MPU regions.
	  A minimum 4-byte alignment is enforced in ARM builds without
	  support for Memory Protection.

if ARM_MPU

config MPU_STACK_GUARD
	bool "Thread Stack Guards"
	help
	  Enable Thread Stack Guards via MPU

config MPU_STACK_GUARD_MIN_SIZE_FLOAT
	int
	depends on MPU_STACK_GUARD
	depends on FPU_SHARING
	default 128
	help
	  Minimum size (and alignment when applicable) of an ARM MPU
	  region, which guards the stack of a thread that is using the
	  Floating Point (FP) context. The width of the guard is set to
	  128, to accommodate the length of a Cortex-M exception stack
	  frame when the floating point context is active. The FP context
	  is only stacked in sharing FP registers mode, therefore, the
	  option is applicable only when FPU_SHARING is selected.

config MPU_ALLOW_FLASH_WRITE
	bool "Add MPU access to write to flash"
	help
	  Enable this to allow MPU RWX access to flash memory

config CUSTOM_SECTION_ALIGN
	bool "Custom Section Align"
	help
	  MPU_REQUIRES_POWER_OF_TWO_ALIGNMENT(ARMv7-M) sometimes cause memory
	  wasting in linker scripts defined memory sections. Use this symbol
	  to guarantee user custom section align size to avoid more memory used
	  for respect alignment. But that needs carefully configure MPU region
	  and sub-regions(ARMv7-M) to cover this feature.

config CUSTOM_SECTION_MIN_ALIGN_SIZE
	int "Custom Section Align Size"
	default 32
	help
	  Custom align size of memory section in linker scripts. Usually
	  it should consume less alignment memory. Although this alignment
	  size is configured by users, it must also respect the power of
	  two regulation if hardware requires.

endif # ARM_MPU

endif # CPU_HAS_MPU