Re: [Patch mm-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling

[Wei Yang]

On Sat, Jun 27, 2026 at 10:59:16AM +0800, Lance Yang wrote:
>
>
>On 2026/6/27 10:07, Wei Yang wrote:
>[...]
>> 
>> Hi David
>> 
>> I did a little adjustment like below. Want to check with you at first.
>> 
>> > 
>> > >From 048ecd33673ec649e168fbbb97749a7c0e344fcd Mon Sep 17 00:00:00 2001
>> > From: "David Hildenbrand (Arm)" <david@xxxxxxxxxx>
>> > Date: Fri, 26 Jun 2026 12:03:40 +0200
>> > Subject: [PATCH] tmp
>> > 
>> > Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>> > ---
>> > mm/page_vma_mapped.c | 29 +++++++++++++++++------------
>> > 1 file changed, 17 insertions(+), 12 deletions(-)
>> > 
>> > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>> > index 2ccbabfb2cc17..ed2a23a90e8dd 100644
>> > --- a/mm/page_vma_mapped.c
>> > +++ b/mm/page_vma_mapped.c
>> > @@ -243,21 +243,31 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> > 		 */
>> > 		pmde = pmdp_get_lockless(pvmw->pmd);
>> > 
>> > -		if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) {
>> > +		if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) ||
>> > +		    pmd_is_device_private_entry(pmde)) {
>> > 			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>> > 			pmde = *pvmw->pmd;
>> > -			if (!pmd_present(pmde)) {
>> > +			if (pmd_is_migration_entry(pmde)) {
>> > 				softleaf_t entry;
>> > 
>> 
>> How about:
>> 				const softleaf_t entry = softleaf_from_pmd(pmde);
>> 
>> > -				if (!thp_migration_supported() ||
>> > -				    !(pvmw->flags & PVMW_MIGRATION))
>> > +				if (!(pvmw->flags & PVMW_MIGRATION))
>> > 					return not_found(pvmw);
>> > 				entry = softleaf_from_pmd(pmde);
>> 
>> could be removed.
>> 
>> > +				if (!check_pmd(softleaf_to_pfn(entry), pvmw))
>> > +					return not_found(pvmw);
>> > +				return true;
>> > +			} else if (pmd_is_device_private_entry(pmde)) {
>> > +				softleaf_t entry;
>> 
>> The same.
>> 
>> > 
>> > -				if (!softleaf_is_migration(entry) ||
>> > -				    !check_pmd(softleaf_to_pfn(entry), pvmw))
>> > +				if (pvmw->flags & PVMW_MIGRATION)
>> > +					return not_found(pvmw);
>> > +				entry = softleaf_from_pmd(pmde);
>> > +				if (!check_pmd(softleaf_to_pfn(entry), pvmw))
>> > 					return not_found(pvmw);
>> > 				return true;
>> > +			} else if (!pmd_present(pmde) ){
>> > +				return not_found(pvmw);
>> > 			}
>> > 			if (likely(pmd_trans_huge(pmde))) {
>> > 				if (pvmw->flags & PVMW_MIGRATION)
>> 
>> How about merge this with above? And put at the first case?
>> 
>> Below is what it looks like:
>
>Why add more churn to a fix with a stable tag? Cleanup can come later no?
>

OK, will leave it for future cleanup.

-- 
Wei Yang
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