Messages in this thread | | | Subject | Re: [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions | From | Florian Fainelli <> | Date | Sun, 15 Aug 2021 09:28:47 +0200 |
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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
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