Re: [PATCH 6.6 v2 1/6] arm64: sysreg: Add layout for ID_AA64MMFR4_EL1

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `EIESB` field in `ID_AA64MMFR4_EL1` is incorrectly defined as a `SignedEnum` instead of an `UnsignedEnum`, which will break cross-CPU feature resolution and capability detection.
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--- Patch [1]: [PATCH 6.6 v2 1/6] arm64: sysreg: Add layout for ID_AA64MMFR4_EL1 ---
commit 553e432fbf7b950e883b1046b692639bcd77b3c1
Author: Marc Zyngier <maz@kernel.org>

arm64: sysreg: Add layout for ID_AA64MMFR4_EL1

ARMv9.5 has introduced ID_AA64MMFR4_EL1 with a bunch of new features. Add the 
corresponding layout.

Link: https://lore.kernel.org/r/20240122181344.258974-5-maz@kernel.org

> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index 76ce150e7347e..f7180d391f829 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -1669,6 +1669,43 @@ UnsignedEnum	3:0	TCRX

[ ... ]

> +UnsignedEnum	11:8	ASID2
> +	0b0000	NI
> +	0b0001	IMP
> +EndEnum
> +SignedEnum	7:4	EIESB
> +	0b0000	NI
> +	0b0001	ToEL3
> +	0b0010	ToELx
> +	0b1111	ANY
> +EndEnum

[Severity: Medium]
Will defining EIESB as a SignedEnum cause issues with capability detection?

If this generates ID_AA64MMFR4_EL1_EIESB_SIGNED as true, it seems like
the cpufeature framework will extract and evaluate the 4-bit field 0b1111 
(ANY) as -1.

Since -1 < 2 (ToELx), could this cause the kernel to fail to detect the ANY
error injection capability or resolve to the wrong capability level on
heterogeneous systems?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260708225124.4130846-1-coltonlewis@google.com?part=1