Arm: Memory Management
- doc
- memory management
- virtual and physical address
- Memory Management Unit (MMU)
- Address spaces
- virtual address space
doc
virtual address -> physical address 映射关系放在Translation table中
software manages the TLBs(Translation Lookaside Buffers)
memory management
软件访问虚拟地址(virtual address space)，处理器转换为物理地址
通过虚拟地址机制，OS可以控制软件访问的权限，天然适合sandbox场景
virtual and physical address
virtual address space: peripherals, kernel data, kernel code, application data, application code
-> Translation Tables
physical address space: ddr, peripherals, flash, sram, rom
注意，Translation Tables一般由OS/hypervisor运行软件维护，在memory中载入
Memory Management Unit (MMU)
MMU负责执行virtual address与physical address的translation：
- table walk unit: 负责执行管理逻辑，并且将Translation Tables读入memory
- Translation Lookaside Buffers (TLBs): 缓存最近的translation
即，先找TLBs，再Table Walk Unit去Memory找
Translation Tables里包含PA base, Attributes
Address spaces
NS.EL1 / NS.EL0 -> Guest OS Tables (stage 1 Translation) -> physical memory map seen by guest os (peripherals, ram, flash) -> Virtualization Tables (stage 2 Translation) -> (peripherals, ram, flash)
NS.EL2 -> Hypervisor Virtual memory map -> Hypervisor Tables -> (peripherals, ram, flash)
EL3 -> Secure Monitor Virtual memory map -> Secure Monitor Tables -> (peripherals, ram, flash)
IPAs: intermediate physical addresses
virtual address space
虚拟地址空间大小可以动态设定，以TCR_ELx.TnSZ动态控制：2^(64 - TCR_ELx.TnSZ)
不能设定比物理地址大的虚拟地址空间。
Address Space Identifiers（ASIDs）：用于标识不同app的虚拟地址空间。
TLB：VA Tag（标识虚拟地址空间前缀——区分Kernel Space, User Space, …）、ASID、Descriptor
Virtual Machine Identifiers: VMID => 区分不同的VM
