The BTB is tagged by all memory space information required
to uniquely identify a virtual memory space, ASID, VMID, security,
and Exception level. All predictions are checked at branch resolution
time to ensure that a legal branch is resolved. Therefore, flushing
the BTB on a context switch is not required. AArch64 state does
not implement BTB flush instructions.
automatically invalidates the BTB when either stage of the MMU is disabled.