linux-kernel - Re: [PATCH v3 06/11] arm64/mm: Hoist barriers out of set_ptes

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Message-ID: <Z-68yPBh1FbRvCoS@arm.com>
Date: Thu, 3 Apr 2025 21:46:44 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Will Deacon <will@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Kevin Brodsky <kevin.brodsky@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 06/11] arm64/mm: Hoist barriers out of
 set_ptes_anysz() loop

On Tue, Mar 04, 2025 at 03:04:36PM +0000, Ryan Roberts wrote:
> set_ptes_anysz() previously called __set_pte() for each PTE in the
> range, which would conditionally issue a DSB and ISB to make the new PTE
> value immediately visible to the table walker if the new PTE was valid
> and for kernel space.
> 
> We can do better than this; let's hoist those barriers out of the loop
> so that they are only issued once at the end of the loop. We then reduce
> the cost by the number of PTEs in the range.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
>  arch/arm64/include/asm/pgtable.h | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index e255a36380dc..1898c3069c43 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -317,13 +317,11 @@ static inline void __set_pte_nosync(pte_t *ptep, pte_t pte)
>  	WRITE_ONCE(*ptep, pte);
>  }
>  
> -static inline void __set_pte(pte_t *ptep, pte_t pte)
> +static inline void __set_pte_complete(pte_t pte)
>  {
> -	__set_pte_nosync(ptep, pte);
> -
>  	/*
>  	 * Only if the new pte is valid and kernel, otherwise TLB maintenance
> -	 * or update_mmu_cache() have the necessary barriers.
> +	 * has the necessary barriers.

Thanks for removing the stale comment.

Reviewed-by: Catalin Marinas <catalin.marinas@....com>