Re: [PATCH] mm/page_vma_mapped: revalidate and do proper check before return device-private pmd

[Lance Yang <lance.yang@linux.dev>]

On 2026/6/22 22:21, Wei Yang wrote:
> On Mon, Jun 22, 2026 at 02:46:40PM +0100, Lorenzo Stoakes wrote:
>> +cc Lance, linux-kernel
>>
>> Your subject line is 83 characters long and is way too detailed how about 'fix
>> device-private PMD handling'?
>>
> 
> Got it.
> 
>> You forgot to include linux-kernel@vger.kernel.org on the mail, lore seems to be
>> a bit broken atm but in general it's helpful to include that.
> 
> Got it.
> 
> So usually we send a patch to both linux-mm and linux-kernel? If so, I
> remember is later actions.

Yeah, please keep linux-kernel copied too. For MM patches, linux-mm +
linux-kernel is the right default, IMHO :)

>>
>> Also is useful to make this [PATCH mm-hotfixes] to make it really clear it's
>> intended as a hotfix.
>>
> 
> Got it.
> 
[...]
>> ----8<----
>> >From e6a3c1c782714ed831c4d46a14bb99226423bf59 Mon Sep 17 00:00:00 2001
>> From: Wei Yang <richard.weiyang@gmail.com>
>> Date: Mon, 22 Jun 2026 13:06:51 +0000
>> Subject: [PATCH] refactored
>>
>> Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
>> ---
>> mm/page_vma_mapped.c | 20 +++++++++++++++-----
>> 1 file changed, 15 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>> index 2ccbabfb2cc1..17dff8aab9f9 100644
>> --- a/mm/page_vma_mapped.c
>> +++ b/mm/page_vma_mapped.c
>> @@ -269,14 +269,24 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>> 			/* THP pmd was split under us: handle on pte level */
>> 			spin_unlock(pvmw->ptl);
>> 			pvmw->ptl = NULL;
>> -		} else if (!pmd_present(pmde)) {
>> -			const softleaf_t entry = softleaf_from_pmd(pmde);
>> +		} else if (pmd_is_device_private_entry(pmde)) {
>> +			softleaf_t entry;
>> +
>> +			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>> +			pmde = *pvmw->pmd;
>> +			entry = softleaf_from_pmd(pmde);
>>
>> -			if (softleaf_is_device_private(entry)) {
>> -				pvmw->ptl = pmd_lock(mm, pvmw->pmd);
>> +			if (likely(softleaf_is_device_private(entry))) {
>> +				if (pvmw->flags & PVMW_MIGRATION)
>> +					return not_found(pvmw);
>> +				if (!check_pmd(softleaf_to_pfn(entry), pvmw))
>> +					return not_found(pvmw);
>> 				return true;
>> 			}
>> -
>> +			/* device-private pmd was split under us: handle on pte level */
>> +			spin_unlock(pvmw->ptl);
>> +			pvmw->ptl = NULL;
>> +		} else if (!pmd_present(pmde)) {
>> 			if ((pvmw->flags & PVMW_SYNC) &&
>> 			    thp_vma_suitable_order(vma, pvmw->address,
>> 						   PMD_ORDER) &&
>> --
>> 2.54.0
> 
> If we prefer this way, I will check and take it.

And +1 on Lorenzo's diff. Much cleaner.

Cheers, Lance