Re: [PATCH v2 1/1] mm/huge_memory: simplify pgtable deposit detection

[David Hildenbrand (Arm)]

On 9/18/26 05:19, Lance Yang wrote:
> 
> On Thu, Sep 17, 2026 at 04:13:59PM -0700, Andrew Morton wrote:
>> On Thu, 17 Sep 2026 13:40:15 +0800 Lance Yang <lance.yang@xxxxxxxxx> wrote:
>>
>>> Whether a PMD has a deposited PTE page table only depends on whether the
>>> architecture requires deposits or the VMA is anonymous.
>>>
>>> Implement this rule directly in vma_has_deposited_pgtable(), avoiding
>>> mistaking a non-anonymous raw PFN PMD for one with a deposit and attempting
>>> to withdraw a page table that was never deposited.
>>
>> A large part of my life is asking $LLM "what are the userspace-visible
>> runtime effects of this bug".  Because NOBODY EVER TELLS ME!!!
> 
> That's on me ... I trimmed too much from v1.
> 
>> This time it says "Processes using PMD-sized raw PFN mappings can
>> trigger a kernel NULL-pointer dereference when the mapping is torn
>> down", which sounds kinda important if true.
> 
> There is no known in-tree workload that triggers it, though. Mostly a
> defensive/simplifying change.

Yeah, it's not a fix.

-- 
Cheers,

David