linux-kernel - Re: [PATCH] arm64: Enable MRS emulation early

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Date:   Wed, 4 Oct 2017 11:14:26 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        matwey.kornilov@...il.com, James Morse <james.morse@....com>,
        Dave Martin <Dave.martin@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, stable@...r.kernel.org
Subject: Re: [PATCH] arm64: Enable MRS emulation early

On Wed, Oct 04, 2017 at 10:48:05AM +0100, Suzuki K Poulose wrote:
> Make sure the MRS emulation is enabled early enough, such that the
> early userspace applications (e.g, those run from initrd) could
> use the facility without crashing them.
> 
> Fixes: commit 77c97b4ee2129 ("arm64: cpufeature: Expose CPUID registers by emulation")
> Reported-by: Matwey V. Kornilov <matwey.kornilov@...il.com>
> Cc: James Morse <james.morse@....com>
> Cc: Dave Martin <Dave.martin@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: stable@...r.kernel.org
> Cc: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>

This looks sensible, but shouldn't we do the same for other
late_inicalls can affect initrd userspace?

e.g. armv8_deprecated_init, fpsimd_init, sys_reg_genericv8_init?

Thanks,
Mark.

> ---
>  arch/arm64/kernel/cpufeature.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 9f9e0064c8c1..276eecab6cea 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
>  	return 0;
>  }
>  
> -late_initcall(enable_mrs_emulation);
> +core_initcall(enable_mrs_emulation);
> -- 
> 2.13.5
>