Re: [PATCH v2 20/20] arm64: Add work around for Arm Cortex-A55 Erratum 1024718

[Dave Martin]

On Wed, Jan 31, 2018 at 06:28:07PM +0000, Suzuki K Poulose wrote:
> Some variants of the Arm Cortex-55 cores (r0p0, r0p1, r1p0) suffer
> from an erratum 1024718, which causes incorrect updates when DBM/AP
> bits in a page table entry is modified without a break-before-make
> sequence. The work around is to skip enabling the hardware DBM feature
> on the affected cores. The hardware Access Flag management features
> is not affected. There are some other cores suffering from this
> errata, which could be added to the midr_list to trigger the work
> around.
> 
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: ckadabi@xxxxxxxxxxxxxx
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Reviewed-by: Dave Martin <Dave.Martin@xxxxxxx>

> ---
>  Documentation/arm64/silicon-errata.txt |  1 +
>  arch/arm64/Kconfig                     | 14 ++++++++++++++
>  arch/arm64/kernel/cpufeature.c         | 14 +++++++++++++-
>  3 files changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
> index b9d93e981a05..5203e71c113d 100644
> --- a/Documentation/arm64/silicon-errata.txt
> +++ b/Documentation/arm64/silicon-errata.txt
> @@ -55,6 +55,7 @@ stable kernels.
>  | ARM            | Cortex-A57      | #834220         | ARM64_ERRATUM_834220        |
>  | ARM            | Cortex-A72      | #853709         | N/A                         |
>  | ARM            | Cortex-A73      | #858921         | ARM64_ERRATUM_858921        |
> +| ARM            | Cortex-A55      | #1024718        | ARM64_ERRATUM_1024718       |
>  | ARM            | MMU-500         | #841119,#826419 | N/A                         |
>  |                |                 |                 |                             |
>  | Cavium         | ThunderX ITS    | #22375, #24313  | CAVIUM_ERRATUM_22375        |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1d51c8edf34b..070efe1f7ec3 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -461,6 +461,20 @@ config ARM64_ERRATUM_843419
>  
>  	  If unsure, say Y.
>  
> +config ARM64_ERRATUM_1024718
> +	bool "Cortex-A55: 1024718: Update of DBM/AP bits without break before make might result in incorrect update"
> +	default y
> +	help
> +	  This option adds work around for Arm Cortex-A55 Erratum 1024718.
> +
> +	  Affected Cortex-A55 cores (r0p0, r0p1, r1p0) could cause incorrect
> +	  update of the hardware dirty bit when the DBM/AP bits are updated
> +	  without a break-before-make. The work around is to disable the usage
> +	  of hardware DBM locally on the affected cores. CPUs not affected by
> +	  erratum will continue to use the feature.
> +
> +	  If unsure, say Y.
> +
>  config CAVIUM_ERRATUM_22375
>  	bool "Cavium erratum 22375, 24313"
>  	default y
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 1f695a998eed..410fbddec129 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -923,9 +923,21 @@ static inline void __cpu_enable_hw_dbm(void)
>  	isb();
>  }
>  
> +static bool cpu_has_erratum_1024718(void)
> +{
> +	static const struct midr_range cpus[] = {
> +		MIDR_RANGE(MIDR_CORTEX_A55, 0, 0, 1, 0),  // A55 r0p0 -r1p0
> +		{},
> +	};
> +
> +	return IS_ENABLED(CONFIG_ARM64_ERRATUM_1024718) &&
> +	       is_midr_in_range_list(read_cpuid_id(), cpus);
> +}
> +
>  static void cpu_enable_hw_dbm(struct arm64_cpu_capabilities const *cap)
>  {
> -	if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU))
> +	if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU) &&
> +	    !cpu_has_erratum_1024718())
>  		__cpu_enable_hw_dbm();
>  }
>  #endif
> -- 
> 2.14.3
> 
> 
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