is relevant to all public releases of the AArch64 Linux kernel.
The AArch64 exception model is made up of a number of exception levels
-(EL0 - EL3), with EL0 and EL1 having a secure and a non-secure
-counterpart. EL2 is the hypervisor level and exists only in non-secure
-mode. EL3 is the highest priority level and exists only in secure mode.
+(EL0 - EL3), with EL0, EL1 and EL2 having a secure and a non-secure
+counterpart. EL2 is the hypervisor level, EL3 is the highest priority
+level and exists only in secure mode. Both are architecturally optional.
For the purposes of this document, we will use the term `boot loader`
simply to define all software that executes on the CPU(s) before control
All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
IRQ and FIQ).
- The CPU must be in either EL2 (RECOMMENDED in order to have access to
- the virtualisation extensions) or non-secure EL1.
+ The CPU must be in non-secure state, either in EL2 (RECOMMENDED in order
+ to have access to the virtualisation extensions), or in EL1.
- Caches, MMUs