linux-kernel - Re: [PATCH 06/10] arm64: mm: Simplify __TLBI_RANGE

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Message-ID: <cf0e85e7-8604-416a-bea6-0a59b5aaedd4@arm.com>
Date: Tue, 15 Jul 2025 10:43:21 +0530
From: Dev Jain <dev.jain@....com>
To: Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>,
 Ryan Roberts <ryan.roberts@....com>, Mark Rutland <mark.rutland@....com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH 06/10] arm64: mm: Simplify __TLBI_RANGE_NUM() macro


On 11/07/25 9:47 pm, Will Deacon wrote:
> Since commit e2768b798a19 ("arm64/mm: Modify range-based tlbi to
> decrement scale"), we don't need to clamp the 'pages' argument to fit
> the range for the specified 'scale' as we know that the upper bits will
> have been processed in a prior iteration.
>
> Drop the clamping and simplify the __TLBI_RANGE_NUM() macro.
>
> Signed-off-by: Will Deacon <will@...nel.org>

Just for the sake of it:

It is easy to check that for natural numbers x and y,

x < (((x >> y) + 1) << y)

This implies x < ((x >> y) << y) + (1 << y)
=> x - ((x >> y) << y) < (1 << y)

Substitute x as pages, and y as 5 * scale + 1, the
inequation means that after the first iteration, the
new value of pages will be strictly less than 1 << (5 * scale + 1)
=> the current scale won't be repeated => the min is redundant.

Reviewed-by: Dev Jain <dev.jain@....com>

> ---
>   arch/arm64/include/asm/tlbflush.h | 6 +-----
>   1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index ddd77e92b268..a8d21e52ef3a 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -205,11 +205,7 @@ static __always_inline void __tlbi_level(const enum tlbi_op op, u64 addr, u32 le
>    * range.
>    */
>   #define __TLBI_RANGE_NUM(pages, scale)					\
> -	({								\
> -		int __pages = min((pages),				\
> -				  __TLBI_RANGE_PAGES(31, (scale)));	\
> -		(__pages >> (5 * (scale) + 1)) - 1;			\
> -	})
> +	(((pages) >> (5 * (scale) + 1)) - 1)
>   
>   /*
>    *	TLB Invalidation