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SubjectRe: [PATCH V2] arm64/cpufeature: Validate feature bits spacing in arm64_ftr_regs[]
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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@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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@arm.com>

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