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

[Lance Yang]

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@xxxxxxxxxxxxxxx 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@xxxxxxxxx>
> > Date: Mon, 22 Jun 2026 13:06:51 +0000
> > Subject: [PATCH] refactored
> >
> > Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> > ---
> > 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