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

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Message-ID: <00bf0498-8f11-466e-9f2a-f7e656ecddf9@arm.com>
Date: Wed, 15 Oct 2025 12:16:18 +0530
From: Dev Jain <dev.jain@....com>
To: Yang Shi <yang@...amperecomputing.com>, ryan.roberts@....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 14/10/25 4:57 am, 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")
> 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);

Why not just use idx as the iterator in the for loop? Using i and then incrementing
idx is confusing.

As noted by Ryan, the fixes commit is wrong. The issues persists from commit c55191e.

After fixing these:

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

>   		}
>   	}