1 MPU

armv8m 上的MPU 有8个region，每一个region都有起始地址，结束地址，访问权限和内存属性。每一个region都有单独的属性。
本文仅以secure MPU为例讲解MPU。
armv8m 上的MPU和armv7m的MPU有一点不同， v8m的MPU不支持overlap，如果一个地址同时出现在两个不同的region中，会导致bus fault。

1.1 Memory attributes summary

Memory Type	Shareability	Other attributes	Description
Device-nGnRnE	Sharable	-	Used to access memory mapped peripherals.All accesses to DevicenGnRnE memory occur in program order. All regions are assumed to be shared
Device-nGnRE	Sharable	-	Used to access memory mapped peripherals.Weaker ordering thanDevice-nGnRnE.
Device-nGRE	Sharable	-	Used to access memory mapped peripherals.Weaker ordering thanDevice-nGnRE.
Device-GRE	Sharable	-	Used to access memory mapped peripherals.Weaker ordering thanDevice-nGRE.
Normal	Sharable	Non-cacheable Write-Through Cacheable Write-Back Cacheable	Normal memory that is shared between several processors.
Normal	Non-Shareable	Non-cacheable Write-Through Cacheable Write-Back Cacheable	Normal memory that only a single processor uses.

1.2 MPU寄存器

Address	Name	Access Type	Reset Value
0xE000ED90	MPU_TYPE	RO	该寄存器的值是固定的，取决于SOC实现
0xE000ED94	MPU_CTRL	RW	0x00000000
0xE000ED98	MPU_RNR	RW	未知
0xE000ED9C	MPU_RBAR	RW	未知
0xE000EDA0	MPU_RLAR	RW	未知
0xE000EDA4	MPU_RBAR_A<n>	RW	未知
0xE000EDA8	MPU_RBAR_A<n>	RW	未知
0xE000EDC0	MPU_MAIR0	RW	未知
0xE000EDC4	MPU_MAIR1	RW	未知

1.2.1 MPU Type Register

MPU_TYPE寄存器用来表示MPU是否存在以及它支持多少个region。

Bits	Name	Function
[31:16]	-	保留位
[15:8]	REGION	0x0-MPU没有region支持 0x8当前MPU 支持8个REGION
[7:1]	-	保留位
[0]	SEPARATE	0

1.2.2 MPU Control Register

MPU_CTRL用来

• 使能MPU
• 使能backgroup map
• 使能NMI中MPU是否有效

Bits	Name	Function
[31:3]	-	保留位
[2]	PRIVDEFENA	使能特权级软件使用default memory map 0 - 关闭default memory map。任何访问没有在region中描述的都会产生bus fault。 1 - 使能default memory map，当它使能后，访问没有在region中memory会使用默认的memory map
[1]	HFNMIENA	使HardFault和NMI时能MPU在 0 - 在HardFault和NMI时， MPU无效 1 - 在HardFault和NMI时， MPU仍然有效
[0]	ENABLE	使能MPU 0 - 关闭MPU 1 - 打开MPU

1.2.3 MPU Region Number Register

MPU_RNR用来选择region，在访问MPU_RBAR和MPU_RLAR之前，必须先写入MPU_RNR来选择region

Bits	Name	Function
[31:8]	-	保留位
[7:0]REGION	REGION索引，如果选择REGION1, 则设为1

1.2.4 MPU Region Base Address Register

MPU_RBAR定义了MPU region的起始地址

Bits	Name	Function
[31:5]	BASE	REGION 基地址
[4:3]	SH	定义了Normal的Shareability属性 0b00 Non-shareable. 0b01 UNPREDICATABLE 0b10 Outer shareable. 0b11 Inner shareable
[2:1]	AP	访问属性 0b00 特权级代码可读写. 0b01 特权级代码可读写 0b10 特权级代码只读. 0b11 所有代码只读
[0]	XN	0 可执行Memory 1 不可执行Memory

1.2.5 MPU Region Limit Address Register

MPU_RLAR定义了REGION的上限地址以及REGION属性选择

Bits	Name	Function
[31:5]	LIMIT	REGION 上限地址
[4]	-	保留位
[3:1]	AttrIndx	属性索引号
[0]	EN	0 不使能REGION 1 使能REGION

1.2.6 MPU Memory Attribute Indirection Registers 0 and 1

MPU_MAIR0

Bits	Name	Function
[31:24]	Attr3	REGION3属性
[23:16]	Attr2	REGION2属性
[15:8]	Attr1	REGION1属性
[7:0]	Attr0	REGION0属性

MPU_MAIR1

Bits	Name	Function
[31:24]	Attr7	REGION7属性
[23:16]	Attr6	REGION6属性
[15:8]	Attr5	REGION5属性
[7:0]	Attr4	REGION4属性

每一个REGION属性MARI_ATTR占8位,如果MAIR_ATTR[7:4]为0：那MAIR_ATTR定义如下:

Bits	Name	Function
[3:2]	Device	0b00 Device-nGnRnE 0b01 Device-nGnRE 0b10 Device-nGRE 0b11 Device-GRE

如果MAIR_ATTR[7:4]不为0， 那么MAIR_ATTR定义如下

Bits	Name	Function
[7:4]	Outer	Outer attributes. Specifies the Outer memory attributes. The possible values of this field are: 0b0000 -Device memory. 00RW -Normal memory, Outer write-through transient (RW is not 00). 0b0100 -Normal memory, Outer non-cacheable. 01RW-Normal memory, Outer write-back transient (RW is not 00).10RW Normal memory, Outer write-through non-transient. 11RW -Normal memory, Outer write-back non-transient. R and W specify the outer read and write allocation policy: 0 = do not allocate, 1 = allocate.
[3:0]	Inner	Inner attributes. Specifies the Inner memory attributes. The possible values of this field are: 0b0000 -UNPREDICTABLE. 00RW- Normal memory, Inner write-through transient (RW is not 00). 0b0100- Normal memory, Inner non-cacheable. 01RW -Normal memory, Inner write-back transient (RW is not 00). 10RW -Normal memory, Inner write-through non-transient. 11RW -Normal memory, Inner write-back non-transient. R and W specify the outer read and write allocation policy: 0 = do not allocate, 1 = allocate.

2 MPU 代码

2.1环境搭建

代码git
MPS2开发板手册

安装qemu-system-arm, 确保该版本下有cortex m33的仿真板

mps2-an385           ARM MPS2 with AN385 FPGA image for Cortex-M3
mps2-an505           ARM MPS2 with AN505 FPGA image for Cortex-M33
mps2-an511           ARM MPS2 with AN511 DesignStart FPGA image for Cortex-M3
mps2-an521           ARM MPS2 with AN521 FPGA image for dual Cortex-M33

安装工具链armv8l-linux-gnueabihf-
运行命令：

make;make qemu

log:

qemu-system-arm -machine mps2-an505 -cpu cortex-m33 \
                    -m 4096 \
		    -nographic \
                    -kernel kernel.elf 
qemu-system-arm: invalid accelerator kvm
qemu-system-arm: falling back to tcg
hello cortex m33
test_func_print entry
test_armv8m_xn:mpu setup done
default_exception_handler entry

2.2 MPU 源码

2.2.1 armv8m_mpu.h

#ifndef _ARMV8M_MPU_H_
#define _ARMV8M_MPU_H_

#include <stdint.h>
#include <stdbool.h>

typedef struct armv8m_mpu_tag {
    
    volatile uint32_t mpu_type;
    volatile uint32_t mpu_ctrl;
    volatile uint32_t mpu_rnr;
    volatile uint32_t mpu_rbar;
    volatile uint32_t mpu_rlar;
    volatile uint32_t reserved[7];
    volatile uint32_t mpu_mair0;
    volatile uint32_t mpu_mair1;
} armv8m_mpu_t;

#define MPU_CTRL_ENABLE_SHITF 0UL
#define MPU_CTRL_ENABLE_MASK (1UL << MPU_CTRL_ENABLE_SHITF)

#define MPU_CTRL_HFNMIENA_SHIFT 1UL
#define MPU_CTRL_HFNMIENA_MASK (1UL << MPU_CTRL_HFNMIENA_SHIFT)

#define MPU_CTRL_PRIVDEFENA_SHIFT 2UL
#define MPU_CTRL_PRIVDEFENA_MASK (1UL << MPU_CTRL_PRIVDEFENA_SHIFT)

#define MPU_RNR_REGION_SHIFT 0UL
#define MPU_RNR_REGION_MASK (0xFFUL << MPU_RNR_REGION_SHIFT)

#define MPU_CTRL_RBAR_BASE_SHIFT 0x5UL
#define MPU_CTRL_RBAR_BASE_MASK 0xFFFFFFE0UL

#define MPU_CTRL_RBAR_SH_SHIFT 3UL
#define MPU_CTRL_RBAR_SH_MASK (0x3UL << MPU_CTRL_RBAR_SH_SHIFT)

#define MPU_CTRL_RBAR_AP_SHIFT 1UL
#define MPU_CTRL_RBAR_AP_MASK (0x3UL << MPU_CTRL_RBAR_AP_SHIFT)

#define MPU_CTRL_RBAR_XN_SHIFT 0UL
#define MPU_CTRL_RBAR_XN_MASK (1UL << MPU_CTRL_RBAR_XN_SHIFT)

#define MPU_CTRL_RLAR_LIMIT_SHIFT 5UL
#define MPU_CTRL_RLAR_LIMIT_MASK 0xFFFFFFE0UL

#define MPU_CTRL_RLAR_ATTRIDX_SHIFT 1UL
#define MPU_CTRL_RLAR_ATTRIDX_MASK (0x7UL << MPU_CTRL_RLAR_ATTRIDX_SHIFT)

#define MPU_CTRL_RLAR_EN_SHIFT 0UL
#define MPU_CTRL_RLAR_EN_MASK (1UL << MPU_CTRL_RLAR_EN_SHIFT)
#define REGION_NON_SHAREABLE 0
#define REGION_UNPREDICTABLE 1
#define REGION_OUTER_SHAREABLE 2
#define REGION_INNER_SHAREABLE 3

#define REGION_RW_PRIV_ONLY 0
#define REGION_RW_ANY 1
#define REGION_RO_PRIV_ONLY 2
#define REGION_RO_ANY 3

#define REGION_X 0
#define REGION_XN 1

#define REGION_DISABLE 0
#define REGION_EN 1

static inline void mpu_disable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl &= ~MPU_CTRL_ENABLE_MASK;
    __asm("dsb");
    __asm("isb");
}

static inline void mpu_enable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl |= MPU_CTRL_ENABLE_MASK;
    __asm("dsb");
    __asm("isb");
}

static inline void mpu_hfnmiena_enable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl |= MPU_CTRL_HFNMIENA_MASK;
}
static inline void mpu_hfnmiena_disable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl &= ~MPU_CTRL_HFNMIENA_MASK;
}

static inline void mpu_privdefena_enable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl |= MPU_CTRL_PRIVDEFENA_MASK;
}

static inline void mpu_privdefena_disable(armv8m_mpu_t *mpu)
{
    
    mpu->mpu_ctrl &= ~MPU_CTRL_PRIVDEFENA_MASK;
}

static inline void mpu_select_region(armv8m_mpu_t *mpu, uint8_t region)
{
    
    mpu->mpu_rnr |= ((region << MPU_RNR_REGION_SHIFT) & MPU_RNR_REGION_MASK);
}

static inline void mpu_set_region_base(armv8m_mpu_t *mpu, uint32_t base,
                        uint8_t share_att, uint8_t ap_att, uint32_t is_xn)
{
    
    mpu->mpu_rbar = 0;
    mpu->mpu_rbar = (base & MPU_CTRL_RBAR_BASE_MASK) |
                    ((share_att << MPU_CTRL_RBAR_SH_SHIFT) & MPU_CTRL_RBAR_SH_MASK) |
                    ((ap_att << MPU_CTRL_RBAR_AP_SHIFT) & MPU_CTRL_RBAR_AP_MASK) |
                    (is_xn & MPU_CTRL_RBAR_XN_MASK);
}

static inline void mpu_set_region_limit(armv8m_mpu_t *mpu, uint32_t limit,
                        uint8_t att_idx, uint8_t en)
{
    
    mpu->mpu_rlar = 0;
    mpu->mpu_rlar = (limit & MPU_CTRL_RLAR_LIMIT_MASK) |
                     ((att_idx << MPU_CTRL_RLAR_ATTRIDX_SHIFT) & MPU_CTRL_RLAR_ATTRIDX_MASK) |
                     (en & MPU_CTRL_RLAR_EN_MASK);
}

        mpu->mpu_mair1 &= ~(0xFF << ((idx - 4) * 8));
        mpu->mpu_mair1 |= (attr << ((idx - 4) * 8));
    }
}

#endif

2.2.2 只读region测试

//测试MPU是否关闭region写权限
void test_armv8m_mpu_write()
{
    
    volatile uint32_t *temp_addr = (volatile uint32_t *)0x30001000UL;
    //关闭MPU前可以在Memory进行读写
    easy_printf("0x30001000:%x\n", *temp_addr);
    *temp_addr = 0x1;
    easy_printf("0x30001000:%x\n", *temp_addr);

    armv8m_mpu_t *mpu = (armv8m_mpu_t *)0xE000ED90;
    mpu_disable(mpu);	//关闭MPU
    mpu_select_region(mpu, 0);	//设置region0
    //设置region0基地址0x30000000，只读不可执行
    mpu_set_region_base(mpu, 0x30000000UL, REGION_NON_SHAREABLE, REGION_RO_PRIV_ONLY, REGION_XN); 
    //设置region0上限为0x30001FFFF， region0使用attr0，并且使能region
    mpu_set_region_limit(mpu, 0x30001FFFUL, 0, REGION_EN);
    //设置region0属性为device memory
    mpu_set_region_attr(mpu, 0, 0); /*device memory*/
    //打开MPU
    mpu_hfnmiena_disable(mpu);
    mpu_privdefena_enable(mpu);
    mpu_enable(mpu);
    easy_printf("%s:mpu setup done\n", __func__);
	//打开MPU后测试是否具有写权限
    easy_printf("0x30001000:%x\n", *temp_addr);
    //程序执行到这会触发hard fault
    *temp_addr = 0x2;
    easy_printf("0x30001000:%x\n", *temp_addr);
    easy_printf("%s done\n", __func__);
}

执行log:

qemu-system-arm: invalid accelerator kvm
qemu-system-arm: falling back to tcg
hello cortex m33
0x30001000:00000000
0x30001000:00000001
test_armv8m_mpu_write:mpu setup done
0x30001000:00000001
default_exception_handler entry

2.2.3 地址overlap测试

oid test_armv8m_mpu_overlap()
{
    
    volatile uint32_t *temp_addr = (volatile uint32_t *)0x30001000UL;
    easy_printf("0x30001000:%x\n", *temp_addr);
    *temp_addr = 0x1;
    easy_printf("0x30001000:%x\n", *temp_addr);

    armv8m_mpu_t *mpu = (armv8m_mpu_t *)0xE000ED90;
    mpu_disable(mpu);

	//设置region0：0x30000000 - 0x30001FFF
	//可读可写，不可执行，device memory
    mpu_select_region(mpu, 0);
    mpu_set_region_base(mpu, 0x30000000UL, REGION_NON_SHAREABLE, REGION_RW_PRIV_ONLY, REGION_XN);
    mpu_set_region_limit(mpu, 0x30001FFFUL, 0, REGION_EN);
    mpu_set_region_attr(mpu, 0, 0); /*device memory*/
	//设置region1：0x30001000 - 0x30001FFF
	//可读可写，不可执行，device memory
    mpu_select_region(mpu, 1);
    mpu_set_region_base(mpu, 0x30001000UL, REGION_NON_SHAREABLE, REGION_RW_PRIV_ONLY, REGION_XN);
    mpu_set_region_limit(mpu, 0x30001FFFUL, 1, REGION_EN);
    mpu_set_region_attr(mpu, 0, 1); /*device memory*/
	//打开MPU
    mpu_hfnmiena_disable(mpu);
    mpu_privdefena_enable(mpu);
    mpu_enable(mpu);
    easy_printf("%s:mpu setup done\n", __func__);
	//打开MPU后，由于0x30001000的地址在region0和region1中重叠了，访问该地址会触发hard fault
	//代码执行到这一句的时候会触发异常
    easy_printf("0x30001000:%x\n", *temp_addr);
    easy_printf("%s done\n", __func__);
}

qemu-system-arm: invalid accelerator kvm
qemu-system-arm: falling back to tcg
hello cortex m33
0x30001000:00000000
0x30001000:00000001
test_armv8m_mpu_overlap:mpu setup done
default_exception_handler entry

2.2.4 执行权限测试

void test_func_print()
{
    
    easy_printf("%s entry\n", __func__);
}

void test_armv8m_xn()
{
    
    /* Inject code at 0x30001000 */
    //在0x300001000地址注入代码test_func
typedef void (*test_func_t)(void);
    volatile uint32_t *temp_addr = (volatile uint32_t *)0x30001000UL;
    test_func_t test_f = (test_func_t )0x30001001;//Thumb指令集，所以函数call的时候地址要加1
    /* 1000041c <test_func>: 1000041c: b500 push {lr} 1000041e: 4801 ldr r0, [pc, #4] ; (10000424 <test_func+0x8>) 10000420: 4780 blx r0 10000422: bd00 pop {pc} 10000424: 100005eb andne r0, r0, fp, ror #11 //100005eb是test_func_print的地址 */
    *temp_addr++ = 0x4801b500;
    *temp_addr++ = 0xbd004780;
    *temp_addr++ = 0x100005eb;
    //使能MPU前可以执行在0x30001000处的test_func
    test_f();
    
    //使能MPU region0：0x30000000 - 0x300010000
    //只读，不可执行，device memory
    armv8m_mpu_t *mpu = (armv8m_mpu_t *)0xE000ED90;
    mpu_disable(mpu);
    mpu_select_region(mpu, 0);
    mpu_set_region_base(mpu, 0x30000100UL, REGION_NON_SHAREABLE, REGION_RO_PRIV_ONLY, REGION_XN);
    mpu_set_region_limit(mpu, 0x30001FFFUL, 0, REGION_EN);
    mpu_set_region_attr(mpu, 0, 0); /*device memory*/
    mpu_hfnmiena_disable(mpu);
    mpu_privdefena_enable(mpu);
    mpu_enable(mpu);
    easy_printf("%s:mpu setup done\n", __func__);
    //使能MPU后不可执行0x30001000的test_func，因此代码执行到这里的时候会触发hardfault
    test_f();
}   

log

qemu-system-arm: invalid accelerator kvm
qemu-system-arm: falling back to tcg
hello cortex m33
test_func_print entry
test_armv8m_xn:mpu setup done
default_exception_handler entry