[PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd()

[PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd()

[Gregory Price]

mmap a VM_PFNMAP region whose ->huge_fault installs a PMD through
vmf_insert_pfn_pmd() - a vfio-pci MMIO BAR does this - then

	mbind(p, len, MPOL_BIND, &mask, maxnode, MPOL_MF_STRICT);

With a stand-in module for the driver:

  BUG: unable to handle page fault for address: fffff96dc0000008
  RIP: 0010:queue_folios_pte_range+0xaf/0x440
   walk_pgd_range+0x52b/0xaf0
   __walk_page_range+0x6a/0x1d0
   walk_page_range_mm_unsafe+0x193/0x230
   queue_pages_range+0x64/0xa0
   do_mbind+0x25e/0x640

queue_folios_pmd(), inlined above, calls pmd_folio() on that PMD.  The pfn
is raw MMIO with no memmap entry, so the folio lands in unpopulated
vmemmap.  Neither guard stops the walk:

  walk_page_test()         skips VM_PFNMAP, but queue_pages_walk_ops
                           supplies ->test_walk, so it never runs
  queue_pages_test_walk()  honours vma_migratable(), but only while
                           MPOL_MF_STRICT is clear

A VM_MIXEDMAP vma needs neither flag, being vma_migratable(), so plain
mbind(MPOL_MF_MOVE) reaches this too - and there the bad folio carries on
into migrate_folio_add() and folio_isolate_lru().  mshv_vtl_low is such a
mapping.

Use vm_normal_folio_pmd() and skip on NULL, as the PTE loop in
queue_folios_pte_range() already does with vm_normal_folio().  The huge
zero PMD moves ahead of the lookup, since vm_normal_folio_pmd() returns
NULL for it and its ACTION_CONTINUE would be lost.

mbind(MPOL_MF_STRICT) over a PMD mapped VM_PFNMAP region now returns 0
rather than -EIO.  The PTE loop already returned 0 there.

Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
---
 mm/mempolicy.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index f1aba551f9f1..85803c845965 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -650,7 +650,8 @@ static inline bool queue_folio_required(struct folio *folio,
 	return node_isset(nid, *qp->nmask) == !(flags & MPOL_MF_INVERT);
 }
 
-static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
+static void queue_folios_pmd(pmd_t *pmd, unsigned long addr,
+			     struct mm_walk *walk)
 {
 	struct folio *folio;
 	struct queue_pages *qp = walk->private;
@@ -661,13 +662,15 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
 			qp->nr_failed++;
 		return;
 	}
-	folio = pmd_folio(pmdval);
-	if (folio_is_zone_device(folio))
-		return;
-	if (is_huge_zero_folio(folio)) {
+	if (is_huge_zero_pmd(pmdval)) {
 		walk->action = ACTION_CONTINUE;
 		return;
 	}
+	folio = vm_normal_folio_pmd(walk->vma, addr, pmdval);
+	if (!folio)
+		return;
+	if (folio_is_zone_device(folio))
+		return;
 	if (!queue_folio_required(folio, qp))
 		return;
 	if (!(qp->flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ||
@@ -700,7 +703,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
-		queue_folios_pmd(pmd, walk);
+		queue_folios_pmd(pmd, addr, walk);
 		spin_unlock(ptl);
 		goto out;
 	}
-- 
2.55.0

Re: [PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd()

[David Hildenbrand (Arm)]

On 8/21/26 16:49, Gregory Price wrote:
> mmap a VM_PFNMAP region whose ->huge_fault installs a PMD through
> vmf_insert_pfn_pmd() - a vfio-pci MMIO BAR does this - then
> 
> 	mbind(p, len, MPOL_BIND, &mask, maxnode, MPOL_MF_STRICT);
> 
> With a stand-in module for the driver:
> 
>   BUG: unable to handle page fault for address: fffff96dc0000008
>   RIP: 0010:queue_folios_pte_range+0xaf/0x440
>    walk_pgd_range+0x52b/0xaf0
>    __walk_page_range+0x6a/0x1d0
>    walk_page_range_mm_unsafe+0x193/0x230
>    queue_pages_range+0x64/0xa0
>    do_mbind+0x25e/0x640
> 
> queue_folios_pmd(), inlined above, calls pmd_folio() on that PMD.  The pfn
> is raw MMIO with no memmap entry, so the folio lands in unpopulated
> vmemmap.  Neither guard stops the walk:
> 
>   walk_page_test()         skips VM_PFNMAP, but queue_pages_walk_ops
>                            supplies ->test_walk, so it never runs
>   queue_pages_test_walk()  honours vma_migratable(), but only while
>                            MPOL_MF_STRICT is clear
> 
> A VM_MIXEDMAP vma needs neither flag, being vma_migratable(), so plain
> mbind(MPOL_MF_MOVE) reaches this too - and there the bad folio carries on
> into migrate_folio_add() and folio_isolate_lru().  mshv_vtl_low is such a
> mapping.
> 
> Use vm_normal_folio_pmd() and skip on NULL, as the PTE loop in
> queue_folios_pte_range() already does with vm_normal_folio().  The huge
> zero PMD moves ahead of the lookup, since vm_normal_folio_pmd() returns
> NULL for it and its ACTION_CONTINUE would be lost.
> 
> mbind(MPOL_MF_STRICT) over a PMD mapped VM_PFNMAP region now returns 0
> rather than -EIO.  The PTE loop already returned 0 there.
> 
> Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject")
> Reported-by: sashiko-bot <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
> ---
>  mm/mempolicy.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index f1aba551f9f1..85803c845965 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -650,7 +650,8 @@ static inline bool queue_folio_required(struct folio *folio,
>  	return node_isset(nid, *qp->nmask) == !(flags & MPOL_MF_INVERT);
>  }
>  
> -static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
> +static void queue_folios_pmd(pmd_t *pmd, unsigned long addr,
> +			     struct mm_walk *walk)
>  {
>  	struct folio *folio;
>  	struct queue_pages *qp = walk->private;
> @@ -661,13 +662,15 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
>  			qp->nr_failed++;
>  		return;
>  	}
> -	folio = pmd_folio(pmdval);
> -	if (folio_is_zone_device(folio))
> -		return;
> -	if (is_huge_zero_folio(folio)) {
> +	if (is_huge_zero_pmd(pmdval)) {
>  		walk->action = ACTION_CONTINUE;
>  		return;
>  	}
> +	folio = vm_normal_folio_pmd(walk->vma, addr, pmdval);
> +	if (!folio)
> +		return


I think this is best written as:

folio = vm_normal_folio_pmd(walk->vma, addr, pmdval);
if (!folio) {
	if (is_huge_zero_pmd(pmdval)) {
		walk->action = ACTION_CONTINUE;
		return;
	}
	return;
}
That way we minimize checks on the expected path.

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH 1/2] mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd()

[Gregory Price]

On Thu, Aug 27, 2026 at 07:05:21PM +0200, David Hildenbrand (Arm) wrote:
> >  	}
> > +	folio = vm_normal_folio_pmd(walk->vma, addr, pmdval);
> > +	if (!folio)
> > +		return
> 
> 
> I think this is best written as:
> 
> folio = vm_normal_folio_pmd(walk->vma, addr, pmdval);
> if (!folio) {
> 	if (is_huge_zero_pmd(pmdval)) {
> 		walk->action = ACTION_CONTINUE;
> 		return;
> 	}
> 	return;
> }
> That way we minimize checks on the expected path.
> 

Sure, i'll spin a v2

> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> 

Thanks!

~Gregory

[PATCH 2/2] mm/madvise: use vm_normal_folio_pmd() in cold/pageout PMD range

[Gregory Price]

mmap a VM_MIXEDMAP region whose ->huge_fault installs a PMD through
vmf_insert_pfn_pmd() - mshv_vtl_low does this, and needs CAP_SYS_ADMIN to
open - then

	madvise(p, PMD_SIZE, MADV_PAGEOUT);

With a stand-in module for the driver:

  BUG: unable to handle page fault for address: fffff587c0000008
  RIP: 0010:madvise_cold_or_pageout_pte_range+0x410/0x9b0
   walk_pgd_range+0x52b/0xaf0
   __walk_page_range+0x6a/0x1d0
   walk_page_range_vma_unsafe+0x8e/0x120
   madvise_pageout+0xb2/0x180
   madvise_vma_behavior+0x46b/0xa90
   do_madvise+0x108/0x190
   __x64_sys_madvise+0x26/0x30

Nothing validates the pfn on the way in:

  can_madv_lru_vma()     rejects VM_PFNMAP, but not VM_MIXEDMAP
  can_fault()            *pfn = vmf->pgoff & ~(mask >> PAGE_SHIFT);
  vmf_insert_pfn_pmd()   no pfn_valid() check
  pmd_folio()            pfn_to_page() -> unpopulated vmemmap

Even with a valid pfn the path is wrong.  The mapping carries no rmap, so
folio_maybe_mapped_shared() sees mapcount 0, and the walker goes on to
folio_deactivate(), or folio_isolate_lru() plus reclaim_pages(), against a
folio this mapping does not own.

Use vm_normal_folio_pmd() and skip on NULL, as the PTE half of this same
walker already does with vm_normal_folio().  The huge zero PMD is already
handled further up by is_huge_zero_pmd().

Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net
Cc: <stable@vger.kernel.org> # v6.19+
Assisted-by: Claude:claude-opus-5
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
---
 mm/madvise.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index ffd6a68320a8..ab362bc482a5 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -393,7 +393,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 			goto huge_unlock;
 		}
 
-		folio = pmd_folio(orig_pmd);
+		folio = vm_normal_folio_pmd(vma, addr, orig_pmd);
+		if (!folio)
+			goto huge_unlock;
 
 		if (folio_is_zone_device(folio))
 			goto huge_unlock;
-- 
2.55.0

Re: [PATCH 2/2] mm/madvise: use vm_normal_folio_pmd() in cold/pageout PMD range

[David Hildenbrand (Arm)]

On 8/21/26 16:49, Gregory Price wrote:
> mmap a VM_MIXEDMAP region whose ->huge_fault installs a PMD through
> vmf_insert_pfn_pmd() - mshv_vtl_low does this, and needs CAP_SYS_ADMIN to
> open - then
> 
> 	madvise(p, PMD_SIZE, MADV_PAGEOUT);
> 
> With a stand-in module for the driver:
> 
>   BUG: unable to handle page fault for address: fffff587c0000008
>   RIP: 0010:madvise_cold_or_pageout_pte_range+0x410/0x9b0
>    walk_pgd_range+0x52b/0xaf0
>    __walk_page_range+0x6a/0x1d0
>    walk_page_range_vma_unsafe+0x8e/0x120
>    madvise_pageout+0xb2/0x180
>    madvise_vma_behavior+0x46b/0xa90
>    do_madvise+0x108/0x190
>    __x64_sys_madvise+0x26/0x30
> 
> Nothing validates the pfn on the way in:
> 
>   can_madv_lru_vma()     rejects VM_PFNMAP, but not VM_MIXEDMAP
>   can_fault()            *pfn = vmf->pgoff & ~(mask >> PAGE_SHIFT);
>   vmf_insert_pfn_pmd()   no pfn_valid() check
>   pmd_folio()            pfn_to_page() -> unpopulated vmemmap
> 
> Even with a valid pfn the path is wrong.  The mapping carries no rmap, so
> folio_maybe_mapped_shared() sees mapcount 0, and the walker goes on to
> folio_deactivate(), or folio_isolate_lru() plus reclaim_pages(), against a
> folio this mapping does not own.
> 
> Use vm_normal_folio_pmd() and skip on NULL, as the PTE half of this same
> walker already does with vm_normal_folio().  The huge zero PMD is already
> handled further up by is_huge_zero_pmd().

The last part doesn't make sense, see below.

> 
> Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject")
> Reported-by: sashiko-bot <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net
> Cc: <stable@vger.kernel.org> # v6.19+
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
> ---
>  mm/madvise.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index ffd6a68320a8..ab362bc482a5 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -393,7 +393,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>  			goto huge_unlock;
>  		}
>  
> -		folio = pmd_folio(orig_pmd);
> +		folio = vm_normal_folio_pmd(vma, addr, orig_pmd);
> +		if (!folio)
> +			goto huge_unlock;
I think you can now drop the is_huge_zero_pmd() check, because
!vm_normal_folio_pmd() includes the huge zero folio.

-- 
Cheers,

David

Re: [PATCH 2/2] mm/madvise: use vm_normal_folio_pmd() in cold/pageout PMD range

[Gregory Price]

On Thu, Aug 27, 2026 at 07:07:38PM +0200, David Hildenbrand (Arm) wrote:
> On 8/21/26 16:49, Gregory Price wrote:
> > 
> > Fixes: 3c8e44c9b369 ("mm: mark special bits for huge pfn mappings when inject")
> > Reported-by: sashiko-bot <sashiko-bot@kernel.org>
> > Closes: https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry%40gourry.net
> > Cc: <stable@vger.kernel.org> # v6.19+
> > Assisted-by: Claude:claude-opus-5
> > Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
> > ---
> >  mm/madvise.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index ffd6a68320a8..ab362bc482a5 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -393,7 +393,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> >  			goto huge_unlock;
> >  		}
> >  
> > -		folio = pmd_folio(orig_pmd);
> > +		folio = vm_normal_folio_pmd(vma, addr, orig_pmd);
> > +		if (!folio)
> > +			goto huge_unlock;
> I think you can now drop the is_huge_zero_pmd() check, because
> !vm_normal_folio_pmd() includes the huge zero folio.
> 

I was err'ing on the side of not removing existing checks, but I can
take a look.  Trivilially - I think you are right.

~Gregory