linux-kernel - Re: [PATCH 5/8] arm64: cpufeature: Factor out checking of AArch32 features

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Message-ID: <95817087-122e-0392-9474-c17ad1f926d2@arm.com>
Date:   Wed, 15 Apr 2020 11:36:48 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu
Cc:     linux-kernel@...r.kernel.org, mark.rutland@....com, maz@...nel.org,
        anshuman.khandual@....com, catalin.marinas@....com,
        saiprakash.ranjan@...eaurora.org, dianders@...omium.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 5/8] arm64: cpufeature: Factor out checking of AArch32
 features

On 04/14/2020 10:31 PM, Will Deacon wrote:
> update_cpu_features() is pretty large, so split out the checking of the
> AArch32 features into a separate function and call it after checking the
> AArch64 features.
> 
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>   arch/arm64/kernel/cpufeature.c | 108 +++++++++++++++++++--------------
>   1 file changed, 61 insertions(+), 47 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 7dfcdd9e75c1..32828a77acc3 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -715,6 +715,65 @@ static int check_update_ftr_reg(u32 sys_id, int cpu, u64 val, u64 boot)
>   	return 1;
>   }
>   
> +static int update_32bit_cpu_features(int cpu, struct cpuinfo_arm64 *info,
> +				     struct cpuinfo_arm64 *boot)
> +{

...

> -
>   	if (id_aa64pfr0_sve(info->reg_id_aa64pfr0)) {
>   		taint |= check_update_ftr_reg(SYS_ZCR_EL1, cpu,
>   					info->reg_zcr, boot->reg_zcr);
> @@ -845,6 +857,8 @@ void update_cpu_features(int cpu,
>   			sve_update_vq_map();
>   	}
>   
> +	taint |= update_32bit_cpu_features(cpu, info, boot);
> +

This relies on the assumption that the id_aa64pfr0 has been sanitised. 
It may be worth adding a comment to make sure people (hacking the
kernel) don't move this around and break that dependency.

Either ways:

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