【问题】
以哪个el去执行是什么意思？执行这条指令就会切到切换指令里指定的el吗？

【回答】
在一个core中，至少有一下Translation regime，AT S12E2R, <Xt> 就是使用EL2 Translation regime完成地址翻译。

Secure EL1&0 translation regime, when EL2 is disabled
Non-secure EL1&0 translation regime, when EL2 is disabled
Secure EL1&0 translation regime, when EL2 is enabled
Non-secure EL1&0 translation regime, when EL2 is enabled
Secure EL2&0 translation regime
Non-secure EL2&0 translation regime
Secure EL2 translation regime
Non-secure EL2 translation regime
Secure EL3 translation regime