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Date: Thu, 28 Jul 2016 17:52:56 +1000
From: Nicholas Piggin <npiggin@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: <linuxppc-dev@ozlabs.org>, haokexin@gmail.com,
 aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [PATCH v3 19/21] powerpc: Add option to use jump label for
 mmu_has_feature()
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On Thu, 28 Jul 2016 00:18:15 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> From: Kevin Hao <haokexin@gmail.com>
> 
> As we just did for CPU features.
> 
> Signed-off-by: Kevin Hao <haokexin@gmail.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/include/asm/mmu.h    | 36
> ++++++++++++++++++++++++++++++++++++
> arch/powerpc/kernel/cputable.c    | 17 +++++++++++++++++
> arch/powerpc/lib/feature-fixups.c |  1 + 3 files changed, 54
> insertions(+)
> 
> v3: Rename to mmu_feature_keys, and NUM_MMU_FTR_KEYS.
>     Use the kconfig.
> 
> diff --git a/arch/powerpc/include/asm/mmu.h
> b/arch/powerpc/include/asm/mmu.h index e3eff365e55d..3900cb7fe7cf
> 100644 --- a/arch/powerpc/include/asm/mmu.h
> +++ b/arch/powerpc/include/asm/mmu.h
> @@ -140,6 +140,41 @@ static inline bool __mmu_has_feature(unsigned
> long feature) return !!(MMU_FTRS_POSSIBLE &
> cur_cpu_spec->mmu_features & feature); }
>  
> +#ifdef CONFIG_JUMP_LABEL_FEATURE_CHECKS
> +#include <linux/jump_label.h>
> +
> +#define NUM_MMU_FTR_KEYS	32
> +
> +extern struct static_key_true mmu_feature_keys[NUM_MMU_FTR_KEYS];
> +
> +extern void mmu_feature_keys_init(void);
> +
> +static __always_inline bool mmu_has_feature(unsigned long feature)
> +{
> +	int i;
> +
> +	if (!(MMU_FTRS_POSSIBLE & feature))
> +		return false;
> +
> +	i = __builtin_ctzl(feature);
> +	return static_branch_likely(&mmu_feature_keys[i]);
> +}

And here.