linux-kernel - Re: [PATCH v1 6/6] arm64: tlb: Set the TTL field in flush_tlb

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Date:   Mon, 20 Apr 2020 14:10:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhenyu Ye <yezhenyu2@...wei.com>
Cc:     mark.rutland@....com, will@...nel.org, catalin.marinas@....com,
        aneesh.kumar@...ux.ibm.com, akpm@...ux-foundation.org,
        npiggin@...il.com, arnd@...db.de, rostedt@...dmis.org,
        maz@...nel.org, suzuki.poulose@....com, tglx@...utronix.de,
        yuzhao@...gle.com, Dave.Martin@....com, steven.price@....com,
        broonie@...nel.org, guohanjun@...wei.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, arm@...nel.org,
        xiexiangyou@...wei.com, prime.zeng@...ilicon.com,
        zhangshaokun@...ilicon.com, kuhn.chenqun@...wei.com
Subject: Re: [PATCH v1 6/6] arm64: tlb: Set the TTL field in flush_tlb_range

On Fri, Apr 03, 2020 at 05:00:48PM +0800, Zhenyu Ye wrote:
> This patch uses the cleared_* in struct mmu_gather to set the
> TTL field in flush_tlb_range().
> 
> Signed-off-by: Zhenyu Ye <yezhenyu2@...wei.com>
> ---
>  arch/arm64/include/asm/tlb.h      | 26 +++++++++++++++++++++++++-
>  arch/arm64/include/asm/tlbflush.h | 14 ++++++++------
>  2 files changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index b76df828e6b7..d5ab72eccff4 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -21,11 +21,34 @@ static void tlb_flush(struct mmu_gather *tlb);
>  
>  #include <asm-generic/tlb.h>
>  
> +/*
> + * get the tlbi levels in arm64.  Default value is 0 if more than one
> + * of cleared_* is set or neither is set.
> + * Arm64 doesn't support p4ds now.
> + */
> +static inline int tlb_get_level(struct mmu_gather *tlb)
> +{
> +	int sum = tlb->cleared_ptes + tlb->cleared_pmds +
> +		  tlb->cleared_puds + tlb->cleared_p4ds;
> +
> +	if (sum != 1)
> +		return 0;
> +	else if (tlb->cleared_ptes)
> +		return 3;
> +	else if (tlb->cleared_pmds)
> +		return 2;
> +	else if (tlb->cleared_puds)
> +		return 1;
> +
> +	return 0;
> +}

That's some mighty wonky code. Please look at the generated asm.