Messages in this thread | | | From | Marc Zyngier <> | Subject | [PATCH 0/5] arm64: Survival kit for SCR_EL3.HCE==0 conditions | Date | Thu, 12 Aug 2021 20:02:08 +0100 |
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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.
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.
M. (drink required)
[0] https://lore.kernel.org/r/53f3a2d2-22f8-edee-2507-d41a4090dad7@gmail.com
Marc Zyngier (5): arm64: Directly expand __init_el2_nvhe_prepare_eret where needed arm64: Handle UNDEF in the EL2 stub vectors arm64: Detect disabled HVC early arm64: Warn on booting at EL2 with HVC disabled arm64: Document the requirement for SCR_EL3.HCE
Documentation/arm64/booting.rst | 5 +++++ arch/arm64/include/asm/el2_setup.h | 6 ------ arch/arm64/include/asm/virt.h | 10 +++++++++ arch/arm64/kernel/head.S | 34 ++++++++++++++++++++++++++++++ arch/arm64/kernel/hyp-stub.S | 19 ++++++++++++++++- arch/arm64/kernel/smp.c | 3 +++ 6 files changed, 70 insertions(+), 7 deletions(-)
-- 2.30.2
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