Hi, I'm working on a hobby project: AARCH64 Hypervisor on Raspberry Pi 4b, to learn about kernel internals, boot process and ARM64 baremetal. I have a problem with trapping and forwarding a psci smc generated by linux kernel. I'll explain everything and what steps I have followed. I'm also using Trusted Firmware-A at EL3 using armstub config. More about TF-A here: https://trustedfirmware-a.readthedocs.io/en/latest/plat/rpi4.html I have posted this in TF-A mailing list as well. I would love to learn from experienced kernel and baremetal hackers here as well. Right now, I'm implementing SMC trapping. I can successfully forward almost all SMCs except for PSCI_CPU_ON_AARCH64. Linux makes these SMCs to bring up secondary CPUs during boot. Here's what I'm trying to do: - trap the PSCI_CPU_ON_AARCH64 SMC, - preserve the entry_point address in global variable - replace the entrypoint with my entrypoint and make the smc to tf-a(or simply forward it.) - when secondary cpus come online at the given address, where I set their stack point and then eret the original address. Secondary cpus won't come online at the given address. Even if I don't change any arguments of CPU_ON smc and forward it as it is, the secondary cpus still won't come online. However, without trapping enabled(HCR_EL2.TSC=0), everything works fine. I tried to debug inside Trusted Firmware. I know that overall path for secondary CPU hotplug in is: CPU released from reset -> (ROM and possibly some other bootloader) -> bl31/aarch64/bl31_entrypoint.S:bl31_warm_entrypoint() -> lib/psci/psci_common.c:psci_warmboot_entrypoint() -> lib/psci/psci_on.c:psci_cpu_on_finish() -> rpi3_pwr_domain_on_finish() I printed at all these points in Trusted Firmware with and without trapping enabled. Here's what I found: Nothing gets printed anywhere in that path if trapping is enabled. However, without trapping enabled, I can print anywhere even in bl31_entrypoint.S:bl31_warm_entrypoint(). What could be the problem? Here's my code: https://github.com/SikkiLadho/Leo/blob/4f272eff39934058a7f989c91aad82eab8104...