linux-kernel - Re: [PATCH] arm64/pageattr: Propagate return value from __change_memory

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Message-ID: <aQjHQt2rYL6av4qw@willie-the-truck>
Date: Mon, 3 Nov 2025 15:16:18 +0000
From: Will Deacon <will@...nel.org>
To: Dev Jain <dev.jain@....com>
Cc: catalin.marinas@....com, ryan.roberts@....com, rppt@...nel.org,
	shijie@...amperecomputing.com, yang@...amperecomputing.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64/pageattr: Propagate return value from
 __change_memory_common

On Mon, Nov 03, 2025 at 11:43:06AM +0530, Dev Jain wrote:
> Post a166563e7ec3 ("arm64: mm: support large block mapping when rodata=full"),
> __change_memory_common has a real chance of failing due to split failure.
> Before that commit, this line was introduced in c55191e96caa, still having
> a chance of failing if it needs to allocate pagetable memory in
> apply_to_page_range, although that has never been observed to be true.
> In general, we should always propagate the return value to the caller.
> 
> Cc: stable@...r.kernel.org
> Fixes: c55191e96caa ("arm64: mm: apply r/o permissions of VM areas to its linear alias as well")
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> Based on Linux 6.18-rc4.
> 
>  arch/arm64/mm/pageattr.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 5135f2d66958..b4ea86cd3a71 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -148,6 +148,7 @@ 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 ret;
>  	int i;
>  
>  	if (!PAGE_ALIGNED(addr)) {
> @@ -185,8 +186,10 @@ 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]),
> +			ret = __change_memory_common((u64)page_address(area->pages[i]),
>  					       PAGE_SIZE, set_mask, clear_mask);
> +			if (ret)
> +				return ret;

Hmm, this means we can return failure half-way through the operation. Is
that something callers are expecting to handle? If so, how can they tell
how far we got?

Will