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Re: [PATCH v4 2/6] arm64: HWCAP: encapsulate elf_hwcap


On Wed, Apr 03, 2019 at 11:56:24AM +0100, Andrew Murray wrote:
> The introduction of AT_HWCAP2 introduced accessors which ensure that
> hwcap features are set and tested appropriately.
> 
> Let's now mandate access to elf_hwcap via these accessors by making
> elf_hwcap static within cpufeature.c.
> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>

Reviewed-by: Dave Martin <Dave.Martin@arm.com>

> ---
>  arch/arm64/include/asm/cpufeature.h | 15 ++++---------
>  arch/arm64/include/asm/hwcap.h      |  7 +++---
>  arch/arm64/kernel/cpufeature.c      | 33 +++++++++++++++++++++++++++--
>  3 files changed, 38 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 347c17046668..a3f028f82def 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -392,19 +392,12 @@ extern DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
>  	for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
>  
>  bool this_cpu_has_cap(unsigned int cap);
> +void cpu_set_feature(unsigned int num);
> +bool cpu_have_feature(unsigned int num);
> +unsigned long cpu_get_elf_hwcap(void);
> +unsigned long cpu_get_elf_hwcap2(void);
>  
> -static inline void cpu_set_feature(unsigned int num)
> -{
> -	WARN_ON(num >= MAX_CPU_FEATURES);
> -	elf_hwcap |= BIT(num);
> -}
>  #define cpu_set_named_feature(name) cpu_set_feature(cpu_feature(name))
> -
> -static inline bool cpu_have_feature(unsigned int num)
> -{
> -	WARN_ON(num >= MAX_CPU_FEATURES);
> -	return elf_hwcap & BIT(num);
> -}
>  #define cpu_have_named_feature(name) cpu_have_feature(cpu_feature(name))
>  
>  /* System capability check for constant caps */
> diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
> index 1f38a2740f7a..509ee0d2fa0f 100644
> --- a/arch/arm64/include/asm/hwcap.h
> +++ b/arch/arm64/include/asm/hwcap.h
> @@ -17,6 +17,7 @@
>  #define __ASM_HWCAP_H
>  
>  #include <uapi/asm/hwcap.h>
> +#include <asm/cpufeature.h>
>  
>  #define COMPAT_HWCAP_HALF	(1 << 1)
>  #define COMPAT_HWCAP_THUMB	(1 << 2)
> @@ -86,14 +87,13 @@
>  #define __khwcap2_feature(x)		(ilog2(HWCAP2_ ## x) + 32)
>  
>  #ifndef __ASSEMBLY__
> -#include <linux/kernel.h>
>  
>  /*
>   * This yields a mask that user programs can use to figure out what
>   * instruction set this cpu supports.
>   */
> -#define ELF_HWCAP		lower_32_bits(elf_hwcap)
> -#define ELF_HWCAP2		upper_32_bits(elf_hwcap)
> +#define ELF_HWCAP		cpu_get_elf_hwcap()
> +#define ELF_HWCAP2		cpu_get_elf_hwcap2()
>  
>  #ifdef CONFIG_COMPAT
>  #define COMPAT_ELF_HWCAP	(compat_elf_hwcap)
> @@ -109,6 +109,5 @@ enum {
>  #endif
>  };
>  
> -extern unsigned long elf_hwcap;
>  #endif
>  #endif
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 986ceeacd19f..a655d1bb1186 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -35,8 +35,8 @@
>  #include <asm/traps.h>
>  #include <asm/virt.h>
>  
> -unsigned long elf_hwcap __read_mostly;
> -EXPORT_SYMBOL_GPL(elf_hwcap);
> +/* Kernel representation of AT_HWCAP and AT_HWCAP2 */
> +static unsigned long elf_hwcap __read_mostly;
>  
>  #ifdef CONFIG_COMPAT
>  #define COMPAT_ELF_HWCAP_DEFAULT	\
> @@ -1947,6 +1947,35 @@ bool this_cpu_has_cap(unsigned int n)
>  	return false;
>  }
>  
> +void cpu_set_feature(unsigned int num)
> +{
> +	WARN_ON(num >= MAX_CPU_FEATURES);
> +	elf_hwcap |= BIT(num);
> +}
> +EXPORT_SYMBOL_GPL(cpu_set_feature);
> +
> +bool cpu_have_feature(unsigned int num)
> +{
> +	WARN_ON(num >= MAX_CPU_FEATURES);
> +	return elf_hwcap & BIT(num);
> +}
> +EXPORT_SYMBOL_GPL(cpu_have_feature);
> +
> +unsigned long cpu_get_elf_hwcap(void)
> +{
> +	/*
> +	 * We currently only populate the first 32 bits of AT_HWCAP. Please
> +	 * note that for userspace compatibility we guarantee that bits 62
> +	 * and 63 will always be returned as 0.
> +	 */
> +	return lower_32_bits(elf_hwcap);
> +}
> +
> +unsigned long cpu_get_elf_hwcap2(void)
> +{
> +	return upper_32_bits(elf_hwcap);
> +}
> +
>  static void __init setup_system_capabilities(void)
>  {
>  	/*
> -- 
> 2.21.0
> 


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