Re: [PATCH 4/5] mm/page_vma_mapped: use huge_ptep_get() for hugetlb

[Dev Jain]

On 26/06/26 8:01 am, Lance Yang wrote:
> 
> On Thu, Jun 25, 2026 at 11:29:53AM +0000, Dev Jain wrote:
>> check_pte() is the final validation step in page_vma_mapped_walk().
>> It reads pvmw->pte with ptep_get() to decide whether the entry maps
>> the PFN range being walked. For hugetlb VMAs, that pointer refers
>> to a hugetlb entry.
>>
>> On arches which provide their own huge_ptep_get() to dereference a huge
>> pte pointer, accessing via ptep_get() would cause pte_pfn(),
>> pte_present() etc to misbehave.
>>
>> It is not clear whether this has a trivially visible effect to userspace.
>>
>> Use huge_ptep_get() to dereference a huge pte pointer.
>>
>> Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
>> ---
>> mm/page_vma_mapped.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>> index 2ccbabfb2cc17..18e1d341f463c 100644
>> --- a/mm/page_vma_mapped.c
>> +++ b/mm/page_vma_mapped.c
>> @@ -107,7 +107,13 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
>> static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
> 
> Just one ordering thing: should this patch come first?
> 
> Patches #01-#03 only reach the new huge_ptep_get() after
> page_vma_mapped_walk() succeeds. But before this patch, hugetlb sill
> goes through check_pte() (still using ptep_get()).

You are right, but do we care? This is not a series meant for adding functionality.
I just sent it as a series because they are similar fixes - the patches are to
be applied individually with no dependency.
> 
>> {
>> 	unsigned long pfn;
>> -	pte_t ptent = ptep_get(pvmw->pte);
>> +	pte_t ptent;
>> +
>> +	if (is_vm_hugetlb_page(pvmw->vma))
>> +		ptent = huge_ptep_get(pvmw->vma->vm_mm, pvmw->address,
>> +				      pvmw->pte);
>> +	else
>> +		ptent = ptep_get(pvmw->pte);
>>
>> 	if (pvmw->flags & PVMW_MIGRATION) {
>> 		const softleaf_t entry = softleaf_from_pte(ptent);
>> -- 
>> 2.43.0
>>
>>
>