Re: [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions

[Florian Fainelli]

On 8/12/2021 9:02 PM, Marc Zyngier wrote:
> Anyone vaguely familiar with the ARMv8 architecture would quickly
> understand that entering the kernel at EL2 without enabling the HVC
> instruction is... living dangerously. But as it turns out [0], there
> is a whole range of (*cough*) "high quality" (*cough*) Broadcom
> systems out there configured exactly like that.

Some Broadcom systems, namely the 4908 and all of those using CFE, they 
later switched to u-boot and ATF and got it right.

> If you are speechless, I'm right with you.
>
> These machines have stopped being able to boot an upstream kernel
> since 5.12, where we changed the way we switch from nVHE to VHE, as
> this relies on the HVC instruction being usable... It is also worth
> noting that these systems have never been able to use KVM. Or kexec.
>
> This small series addresses the issue by detecting an UNDEFing HVC in
> a fairly controlled environment, and in this case pretend that we have
> booted at EL1. It also documents the requirement for SCR_EL3.HCE to be
> set to *1* if the kernel is entered at EL2. Turns out that we really
> have to state the obvious.
>
> This has been tested on a FVP model with a hacked-up boot-wrapper.
>
> Note that I really don't think any of this is -stable material, except
> maybe for the documentation. It isn't 5.14 material either. Best case,
> this is 5.15, or maybe even later. If ever.

While I am very appreciative of the work you have done here to try to 
get the dysfunctional systems to warn and continue to boot, I would 
rather we try to load a minimal shim at EL3 capable of fixing up any 
incorrect EL3 register setting ahead of loading the kernel provided this 
is possible at all on a commercially available system. Rafal, is this 
something that CFE allows you to do (as I could not get a straight 
answer from that team), if so have you tried it?
--
Florian