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

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Message-ID: <8943fe0e-0bf7-49a4-bf58-efe08bfd037d@os.amperecomputing.com>
Date: Thu, 16 Oct 2025 11:45:43 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Dev Jain <dev.jain@....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 10/14/25 11:46 PM, Dev Jain wrote:
>
> 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.

You meant something like:

while (idx < idx + numpages)

It is fine to me.

>
> 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>

Thank you.

Yang

>
>>           }
>>       }