tree c64b8afc219b70fd50706a7cabf32e36bbc9159c
parent 5cfe515dfec6e660a2a6a0ee5f7c4f46f7734d1d
author Manish Pandey <manish.pandey2@arm.com> 1702066409 +0000
committer Manish Pandey <manish.pandey2@arm.com> 1709124449 +0000

feat(el3-runtime): introduce UNDEF injection to lower EL

For a feature to be used at lower ELs, EL3 generally needs to disable
the trap so that lower ELs can access the system registers associated
with the feature. Lower ELs generally check ID registers to dynamically
detect if a feature is present (in HW) or not while EL3 Firmware relies
statically on feature build macros to enable a feature.

If a lower EL accesses a system register for a feature that EL3 FW is
unaware of, EL3 traps the access and panics. This happens mostly with
EL2 but sometimes VMs can also cause EL3 panic.

To provide platforms with capability to mitigate this problem, UNDEF
injection support has been introduced which injects a synchronous
exception into the lower EL which is supposed to handle the
synchronous exception.

The current support is only provided for aarch64.

The implementation does the following on encountering sys reg trap

 - Get the target EL, which can be either EL2 or EL1
 - Update ELR_ELx with ELR_EL3, so that after UNDEF handling in lower EL
   control returns to original location.
 - ESR_ELx with EC_UNKNOWN
 - Update ELR_EL3 with vector address of sync exception handler with
   following possible causes
     - Current EL with SP0
     - Current EL with SPx
     - Lower EL using AArch64
 - Re-create SPSR_EL3 which will be used to generate PSTATE at ERET

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I1b7bf6c043ce7aec1ee4fc1121c389b490b7bfb7