Re: [PATCH v2 2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

[Catalin Marinas]

On Tue, Dec 17, 2019 at 06:33:57PM +0000, Suzuki K Poulose wrote:
> In-kernel users of NEON rely on may_use_simd() to check if the SIMD
> can be used. However, we must initialize the SVE before SIMD can
> be used. Add a sanity check to make sure that we have completed the
> SVE setup before anyone uses the SIMD.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> Discussion here : https://lkml.kernel.org/r/20191014145204.GS27757@xxxxxxx

Re-reading this thread, I think the conclusion was more towards having a
WARN_ON in system_supports_fpsimd() (or may_use_simd()). We don't expect
code to start using neon before the SMP is initialised (other than
early_initcall(), the rest run after the secondary CPUs are brought up).

-- 
Catalin