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

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Message-ID: <07a70cbf-dbb5-4444-8393-24c49e53a93f@arm.com>
Date: Fri, 17 Oct 2025 00:17:13 +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 17/10/25 12:15 am, Yang Shi wrote:
>
>
> 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.

for loop is simpler :)


>
>>
>> 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
>
>>
>>>           }
>>>       }
>