ARM-A架构入门基础（三）MMU

14天学习训练营导师课程：周贺贺《ARMv8/ARMv9架构-快速入门》

1. MMU（Memory Management Unit）

内存管理单元，MMU的意义在于将软件程序的虚拟地址转换为真实的物理地址。

2. MMU种类

1. Secure EL1&0 translation regime, when EL2 is disabled
2. Non-secure EL1&0 translation regime, when EL2 is disabled
3. SECURE EL1&0 translation regime, when EL2 is enabled
4. Non-secure EL1&0 translation regime, when EL2 is enabled
5. Secure EL2&0 translation regime
6. Non-secure EL2&0 translation regime
7. Secure EL2 translation regime
8. Non-secure EL2 translation regime
9. Secure EL3 translation regime

3. 如何开启MMU

1. 设置页表基地址TTBR
2. 初始化MAIR_EL3
3. 配置TCR_EL3
4. 创建页表
5. 使能MMU

4. MMU模型

5. 页表属性

PBHA, bits[62:59] : for FEAT_HPDS2
XN or UXN, bit[54] : Execute-never or Unprivileged execute-never
PXN, bit[53] : Privileged execute-never
Contiguous, bit[51] : translation table entry 是连续的，可以存在一个TLB Entry中
DBM, bit[51] : Dirty Bit Modifier
GP, bit[50] : for FEAT_BTI
nT, bit[16] : for FEAT_BBM
nG, bit[11] : 缓存在TLB中的翻译，是否使用ASID标识
AF, bit[10] : Access flag, AF=0后，第一次访问该页面时，会将该标志置为1
SH, bits[9:8] : shareable属性
AP[2:1], bit[7:6] : Data Access Permissions bits
NS, bit[5] : Non-secure bit
Attrlndx[2:0], bits[4:2]

6. 内存属性

R or W	Meaning
0b0	No Allocate
0b1	Allocate

dd	Meaning
0b00	Device-nGnRnE memory
0b01	Device-nGnRE memory
0b10	Device-nGRE memory
0b11	Device-GRE memory