Re: [PATCH v2 1/7] arm64: Introduce system_capabilities_finalized() marker

[Catalin Marinas]

On Tue, Dec 17, 2019 at 06:33:56PM +0000, Suzuki K Poulose wrote:
> We finalize the system wide capabilities after the SMP CPUs
> are booted by the kernel. This is used as a marker for deciding
> various checks in the kernel. e.g, sanity check the hotplugged
> CPUs for missing mandatory features.
> 
> However there is no explicit helper available for this in the
> kernel. There is sys_caps_initialised, which is not exposed.
> The other closest one we have is the jump_label arm64_const_caps_ready
> which denotes that the capabilities are set and the capability checks
> could use the individual jump_labels for fast path. This is
> performed before setting the ELF Hwcaps, which must be checked
> against the new CPUs. We also perform some of the other initialization
> e.g, SVE setup, which is important for the use of FP/SIMD
> where SVE is supported. Normally userspace doesn't get to run
> before we finish this. However the in-kernel users may
> potentially start using the neon mode. So, we need to
> reject uses of neon mode before we are set. Instead of defining
> a new marker for the completion of SVE setup, we could simply
> reuse the arm64_const_caps_ready and enable it once we have
> finished all the setup. Also we could expose this to the
> various users as "system_capabilities_finalized()" to make
> it more meaningful than "const_caps_ready".
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>