Re: [PATCH] KVM: arm64: Allow PSCI SYSTEM_OFF/RESET to return

Marc Zyngier
2020-12-30T10:08:09Z

On 2020-12-29 17:04, Russell King - ARM Linux admin wrote:
> On Tue, Dec 29, 2020 at 04:00:59PM +0000, David Brazdil wrote:
>> The KVM/arm64 PSCI relay assumes that SYSTEM_OFF and SYSTEM_RESET
>> should
>> not return, as dictated by the PSCI spec. However, there is firmware
>> out
>> there which breaks this assumption, leading to a hyp panic. Make KVM
>> more robust to broken firmware by allowing these to return.
>
> Are you sure you should just return?
>
> We've had issues in the past with Linux reboot(2) that returns
> to userspace, allowing on 32-bit ARM for example watchdogs to
> unexpectedly continue being serviced.

I don't think this changes anything compared to the case where
the PSCI relay isn't enabled. The EL1 part of the kernel would
see the SYSTEM_RESET call return, and handle it accordingly
(stay in a while(1) loop).

This is consistent with the PSCI relay design goal of being
invisible to the EL1 kernel.

Thanks,

M.
--
Jazz is not dead. It just smells funny...