linux-kernel - Re: [PATCH 2/3] arm64: mmu: early_pgtable

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Message-ID: <20190213112136.GB22119@lakrids.cambridge.arm.com>
Date:   Wed, 13 Feb 2019 11:21:36 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "yaojun8558363@...il.com" <yaojun8558363@...il.com>,
        "cpandya@...eaurora.org" <cpandya@...eaurora.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "van.freenix@...il.com" <van.freenix@...il.com>
Subject: Re: [PATCH 2/3] arm64: mmu: early_pgtable_alloc: remove unnecessary
 comments

On Wed, Feb 13, 2019 at 09:37:29AM +0000, Peng Fan wrote:
> The empty zero page has been moved to bss area by
> commit 5227cfa71f9e ("arm64: mm: place empty_zero_page in bss"),
> and it alreay added "dsb     ishst" in head.S to make sure the empty
> zero page visible to PTW.
> 
> There is no code to reflect the comment, so remove it.

The comment below refers to the memory pointed to by ptr, which is
zeroed by the memset. The comment does not refer to the generic
empty_zero_page.

This comment is correct, and should stay. Please drop this patch.

Thanks,
Mark.

> 
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
>  arch/arm64/mm/mmu.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 065202da3ad2..f61fa7c8fd2e 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -113,10 +113,6 @@ static phys_addr_t __init early_pgtable_alloc(void)
>  
>  	memset(ptr, 0, PAGE_SIZE);
>  
> -	/*
> -	 * Implicit barriers also ensure the zeroed page is visible to the page
> -	 * table walker
> -	 */
>  	pte_clear_fixmap();
>  
>  	return phys;
> -- 
> 2.16.4
>