Messages in this thread | | | Date | Sun, 15 Aug 2021 10:27:28 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions |
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On Sun, 15 Aug 2021 08:28:47 +0100, Florian Fainelli <f.fainelli@gmail.com> wrote: > > > > 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.
Do we have a list of the affected systems?
> > > > > 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.
That would be the best thing to do, and would make the machine fully usable. I still think we need to have something in the kernel to at least let the user know that their system is misconfigured though.
If CFE allows a payload to be loaded at EL3 and executed on all CPUs, that would be absolutely awesome. It would even allow switching over to ATF...
Thanks,
M.
> 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 >
-- Without deviation from the norm, progress is not possible.
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