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

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Message-ID: <f594696b-ba33-4c04-9cf5-e88767221ae0@os.amperecomputing.com>
Date: Mon, 3 Nov 2025 10:45:42 -0800
From: Yang Shi <yang@...amperecomputing.com>
To: Will Deacon <will@...nel.org>, Dev Jain <dev.jain@....com>
Cc: catalin.marinas@....com, ryan.roberts@....com, rppt@...nel.org,
 shijie@...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 11/3/25 7:16 AM, Will Deacon wrote:
> 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?

IIUC the callers don't have to know whether it is half-way or not 
because the callers will change the permission back (e.g. to RW) for the 
whole range when freeing memory.

Thanks,
Yang

>
> Will