linux-kernel - Re: [PATCH v3 1/2] arm64: pageattr: Use pagewalk API to change memory permissions

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Message-ID: <aE53Jp7ZGgTxtxwG@kernel.org>
Date: Sun, 15 Jun 2025 10:32:54 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, david@...hat.com, catalin.marinas@....com,
	will@...nel.org, lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com, vbabka@...e.cz, surenb@...gle.com,
	mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	suzuki.poulose@....com, steven.price@....com, gshan@...hat.com,
	linux-arm-kernel@...ts.infradead.org, yang@...amperecomputing.com,
	ryan.roberts@....com, anshuman.khandual@....com
Subject: Re: [PATCH v3 1/2] arm64: pageattr: Use pagewalk API to change
 memory permissions

On Fri, Jun 13, 2025 at 07:13:51PM +0530, Dev Jain wrote:
> -/*
> - * This function assumes that the range is mapped with PAGE_SIZE pages.
> - */
> -static int __change_memory_common(unsigned long start, unsigned long size,
> +static int ___change_memory_common(unsigned long start, unsigned long size,
>  				pgprot_t set_mask, pgprot_t clear_mask)
>  {
>  	struct page_change_data data;
> @@ -61,9 +140,28 @@ static int __change_memory_common(unsigned long start, unsigned long size,
>  	data.set_mask = set_mask;
>  	data.clear_mask = clear_mask;
>  
> -	ret = apply_to_page_range(&init_mm, start, size, change_page_range,
> -					&data);
> +	arch_enter_lazy_mmu_mode();
> +
> +	/*
> +	 * The caller must ensure that the range we are operating on does not
> +	 * partially overlap a block mapping. Any such case should either not
> +	 * exist, or must be eliminated by splitting the mapping - which for
> +	 * kernel mappings can be done only on BBML2 systems.
> +	 *
> +	 */
> +	ret = walk_kernel_page_table_range_lockless(start, start + size,
> +						    &pageattr_ops, NULL, &data);

x86 has a cpa_lock for set_memory/set_direct_map to ensure that there's on
concurrency in kernel page table updates. I think arm64 has to have such
lock as well.

> +	arch_leave_lazy_mmu_mode();
> +
> +	return ret;
> +}

-- 
Sincerely yours,
Mike.