linux-kernel - Re: [PATCH 1/2] arm64: mm: make linear mapping permission update more robust for patial range

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Message-ID: <973e36b9-e89a-43b2-bb85-b00343dd4e36@arm.com>
Date: Tue, 14 Oct 2025 09:05:05 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Yang Shi <yang@...amperecomputing.com>, dev.jain@....com, cl@...two.org,
 catalin.marinas@....com, will@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: mm: make linear mapping permission update more
 robust for patial range

On 14/10/2025 00:27, Yang Shi wrote:
> The commit fcf8dda8cc48 ("arm64: pageattr: Explicitly bail out when changing
> permissions for vmalloc_huge mappings") made permission update for
> partial range more robust. But the linear mapping permission update
> still assumes update the whole range by iterating from the first page
> all the way to the last page of the area.
> 
> Make it more robust by updating the linear mapping permission from the
> page mapped by start address, and update the number of numpages.
> 
> Fixes: fcf8dda8cc48 ("arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings")

I don't think this is the correct commit. I think this theoretical issue was
present before that. But it is only theoretical AFAIK? In which case, I'd be
inclined to just drop the tag.

Otherwise, LGTM:

Reviewed-by: Ryan Roberts <ryan.roberts@....com>

> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
> ---
>  arch/arm64/mm/pageattr.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 5135f2d66958..c21a2c319028 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -148,7 +148,6 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	unsigned long size = PAGE_SIZE * numpages;
>  	unsigned long end = start + size;
>  	struct vm_struct *area;
> -	int i;
>  
>  	if (!PAGE_ALIGNED(addr)) {
>  		start &= PAGE_MASK;
> @@ -184,8 +183,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	 */
>  	if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
>  			    pgprot_val(clear_mask) == PTE_RDONLY)) {
> -		for (i = 0; i < area->nr_pages; i++) {
> -			__change_memory_common((u64)page_address(area->pages[i]),
> +		unsigned long idx = (start - (unsigned long)area->addr) >> PAGE_SHIFT;
> +		for (int i = 0; i < numpages; i++) {
> +			__change_memory_common((u64)page_address(area->pages[idx++]),
>  					       PAGE_SIZE, set_mask, clear_mask);
>  		}
>  	}