Re: [PATCH V2] mm/debug_vm_pgtable: Add [pte|pmd]_mkwrite_novma() tests

["Huang, Ying" <ying.huang@linux.alibaba.com>]

David Hildenbrand <david@redhat.com> writes:

> On 22.10.25 10:11, Huang, Ying wrote:
>> Anshuman Khandual <anshuman.khandual@arm.com> writes:
>> 
>>> On 22/10/25 1:03 PM, Huang, Ying wrote:
>>>> Anshuman Khandual <anshuman.khandual@arm.com> writes:
>>>>
>>>>> Add some [pte|pmd]_mkwrite_novma() relevant tests.
>>>>>
>>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>>> Cc: David Hildenbrand <david@redhat.com>
>>>>> Cc: Huang Ying <ying.huang@linux.alibaba.com>
>>>>> Cc: linux-mm@kvack.org
>>>>> Cc: linux-kernel@vger.kernel.org
>>>>> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>>>> ---
>>>>> These tests clear on arm64 platform after the following recent patch.
>>>>>
>>>>> https://lore.kernel.org/all/20251015023712.46598-1-ying.huang@linux.alibaba.com/
>>>>>
>>>>> Changes in V2:
>>>>>
>>>>> - Added a new test combination per Huang
>>>>>
>>>>> Changes in V1:
>>>>>
>>>>> https://lore.kernel.org/all/20251021024424.2390325-1-anshuman.khandual@arm.com/
>>>>>
>>>>>   mm/debug_vm_pgtable.c | 12 ++++++++++++
>>>>>   1 file changed, 12 insertions(+)
>>>>>
>>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>>> index 830107b6dd08..def344bb4a32 100644
>>>>> --- a/mm/debug_vm_pgtable.c
>>>>> +++ b/mm/debug_vm_pgtable.c
>>>>> @@ -102,6 +102,12 @@ static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx)
>>>>>   	WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte, args->vma))));
>>>>>   	WARN_ON(pte_dirty(pte_wrprotect(pte_mkclean(pte))));
>>>>>   	WARN_ON(!pte_dirty(pte_wrprotect(pte_mkdirty(pte))));
>>>>> +
>>>>> +	WARN_ON(!pte_dirty(pte_mkwrite_novma(pte_mkdirty(pte))));
>>>>> +	WARN_ON(pte_dirty(pte_mkwrite_novma(pte_mkclean(pte))));
>>>>> +	WARN_ON(!pte_write(pte_mkdirty(pte_mkwrite_novma(pte))));
>>>>
>>>> Why do you use
>>>>
>>>> pte_mkwrite_novma(pte)
>>>>
>>>> instead of
>>>>
>>>> pte_mkwrite(pte, args->vma)
>>> Just wanted to have more coverage for pte_mkwrite_novma() helper which was missing
>>> till now in this test. But just wondering is there a specific reason for replacing
>>> this with pte_mkwrite() helper instead here ? Also we could probably add tests for
>>> both these helper variations if that is preferred.
>> IIUC, pte_mkwrite() is a more formal interface.  pte_mkwrite_novma()
>> is
>> used to implement pte_mkwrite().  So, IMHO, we should use the more
>> formal pte_mkwrite() interface if possible.
>
> pte_mkwrite() does different things based on VMA flags on some archs
> (e.g., x86). So to test the "interesting" stuff one would have to
> craft a special VMA.
>
> Without any special flags pte_mkwrite() really is just pte_mkwrite_novma().

Thanks for explanation.  If so, I'm fine to use pte_mkwrite_novma() in
the tests.

---
Best Regards,
Huang, Ying