On Mon, Apr 01, 2019 at 11:45:11AM +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.
Looks reasonable except for a couple of minor nits below.
I had wondered whether putting these accessors out of line would affect
any hot paths, but I can't see these used from anything that looks like
a hot path. So we're probably fine.
cpus_have_const_cap() is preferred for places where this matters,
anyway.
[...]
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 986ceeacd19f..84ca52fa75e5 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -35,8 +35,7 @@
> #include <asm/traps.h>
> #include <asm/virt.h>
>
> -unsigned long elf_hwcap __read_mostly;
> -EXPORT_SYMBOL_GPL(elf_hwcap);
> +static unsigned long elf_hwcap __read_mostly;
Now that this doesn't correspond directly to ELF_HWCAP any more and we
hide it, can we rename it to avoid confusion?
Maybe "kernel_hwcap"?
> #ifdef CONFIG_COMPAT
> #define COMPAT_ELF_HWCAP_DEFAULT \
> @@ -1947,6 +1946,35 @@ 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 bit 62
> + * will always be returned as 0.
> + */
Presumably also bit 63?
It is reasonable to say this here, but I think there should also be a
note in Documentation/arm64/elf_hwcaps.txt.
[...]
Cheers
---Dave
