Exception Model
=================

`AArch64 Exception model <https://developer.arm.com/architectures/learn-the-architecture/exception-model>`_

Exception Level: EL0 (Application), EL1(Rich OS), EL2(Hypervisor), EL3(Firmware/Secure Monitor)

不同Level的权限不同，主要是两类权限：

- Memory Privilege（访问内存）: 通过MMU管控。EL0是非特权模式，EL1/2/3要做权限检查。

- Register Access(访问处理器资源)

exception types
==================

synchronous exceptions: caused by, or related to, the instruction that has just been executed

asynchronous exceptions: generated externally, not synchronous with the current instruction stream

- Physical interrupts: SError(system error), IRQ, FIQ

- Virtual interrupts: vSError, vIRQ, vFIQ

不同的level收到不同的type的exception，根据对应的访问控制策略处理