linux-kernel - Re: [PATCH V2] arm64/cpufeature: Validate feature bits spacing in arm64_ftr

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Date:   Tue, 7 Jul 2020 10:58:34 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     anshuman.khandual@....com, linux-arm-kernel@...ts.infradead.org
Cc:     catalin.marinas@....com, will@...nel.org, broonie@...nel.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] arm64/cpufeature: Validate feature bits spacing in
 arm64_ftr_regs[]

Hi Anshuman,

On 07/01/2020 06:25 AM, Anshuman Khandual wrote:
> arm64_feature_bits for a register in arm64_ftr_regs[] are in a descending
> order as per their shift values. Validate that these features bits are
> defined correctly and do not overlap with each other. This check protects
> against any inadvertent erroneous changes to the register definitions.

The patch looks fine to me. I have a few minor nits on the coding
style, feel free to ignore.


> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Applies on 5.8-rc3.
> 
> Changes in V2:
> 
> - Replaced WARN_ON() with WARN() dropping the conditional block per Suzuki
> 
> Changes in V1: (https://patchwork.kernel.org/patch/11606285/)
> 
>   arch/arm64/kernel/cpufeature.c | 45 +++++++++++++++++++++++++++++++---
>   1 file changed, 42 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 9f63053a63a9..7bd7e6f936a5 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -697,11 +697,50 @@ static s64 arm64_ftr_safe_value(const struct arm64_ftr_bits *ftrp, s64 new,
>   
>   static void __init sort_ftr_regs(void)
>   {
> -	int i;
> +	

> +	unsigned int i;


> +
> +	for (i = 0; i < ARRAY_SIZE(arm64_ftr_regs); i++) {
	 const struct arm64_ftr_reg *ftr_reg = arm64_ftr_regs[i].reg;
  	 const struct arm64_ftr_bits *ftr_bits = ftr_reg->ftr_bits;
	 unsigned int j = 0;

> +		/*
> +		 * Features here must be sorted in descending order with respect
> +		 * to their shift values and should not overlap with each other.
> +		 */
> +		ftr_reg = arm64_ftr_regs[i].reg;
> +		for (ftr_bits = ftr_reg->ftr_bits,
> +				ftr_bits->width != 0; ftr_bits++, j++) {
			unsigned int shift = ftr_bits->shift;
			unsigned int width = ftr_bits->width;
			unsigned int prev_shift;

> +			WARN((ftr_bits->shift  + ftr_bits->width) > 64,
> +				"%s has invalid feature at shift %d\n",
> +				ftr_reg->name, ftr_bits->shift);

			WARN(shit + width > 64, ....);


Either way,

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>