Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 2/11/26 01:58, Ackerley Tng wrote:
> Ackerley Tng <ackerleytng@google.com> writes:
> 
>> "David Hildenbrand (Arm)" <david@kernel.org> writes:
>>
>>>
>>> Yes. If there is no guest_memfd we wouldn't need it.
>>>
>>
>> Seems like on 5.15.199 there's a hugepage_vma_check(), which will return
>> false since secretmem has vma->vm_ops defined [1], so secretmem VMAs are
>> skipped.
>>
>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/khugepaged.c?h=v5.15.199#n469
>>
> 
> On 6.1.162, secretmem VMAs are skipped since secretmem VMAs are not
> anonymous [2].
> 
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/huge_memory.c?h=v6.1.162#n135
> 
> Same for 6.6.123 [3].
> 
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/huge_memory.c?h=v6.6.123#n125
> 
> It breaks in 6.12.69 [4].


Do you have a reproducer? If so, which behavior does it trigger?

I would assume that we would suddenly have secretmem pages (THP) that 
have a directmap. Or some page copy would crash the kernel.

-- 
Cheers,

David