Subject: [PATCH v3 2/2] arm64: don't flag non-aliasing VIPT I-caches as aliasing

From: [email-masked] (Will Deacon)
Date: Thu, 7 Aug 2014 18:28:07 +0100

On Wed, Aug 06, 2014 at 04:46:06PM +0100, Ard Biesheuvel wrote:
> VIPT caches are non-aliasing if the index is derived from address bits that
> are always equal between VA and PA. Classifying these as aliasing results in
> unnecessary flushing which may hurt performance.
> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>
> ---
> v2, v3: no changes
> 
>  arch/arm64/kernel/cpuinfo.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> index 319255ff536d..a5b6dce48094 100644
> --- a/arch/arm64/kernel/cpuinfo.c
> +++ b/arch/arm64/kernel/cpuinfo.c
> @@ -49,7 +49,13 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
>  	unsigned int cpu = smp_processor_id();
>  	u32 l1ip = CTR_L1IP(info->reg_ctr);
>  
> -	if (l1ip != ICACHE_POLICY_PIPT)
> +	/*
> +	 * VIPT caches are non-aliasing if the VA always equals the PA in all
> +	 * bit positions that are covered by the index, i.e., if num_sets_shift
> +	 * is less than or equal to PAGE_SHIFT minus line_size_shift.
> +	 */
> +	if (l1ip != ICACHE_POLICY_PIPT && !(l1ip == ICACHE_POLICY_VIPT &&
> +	    icache_get_linesize() * icache_get_numsets() <= PAGE_SIZE))

Might just be me, but I'd find this a lot easier to understand if you had a
local `way_size' variable and set it to linesize * num_sets.

Either way:

  Acked-by: Will Deacon <[email-masked]>

Will