[PATCH v2 0/3] mm: cleanup clear_not_present_full_ptes()

[PATCH v2 0/3] mm: cleanup clear_not_present_full_ptes()

[David Hildenbrand (Arm)]

While doing some review, I stumbled over clear_not_present_full_ptes()
and concluded that it needs some love.

Let's remove pte_clear_not_present_full() and cleanup
clear_not_present_full_ptes(), renaming it to clear_non_present_ptes().

Heavily build-tested, runtime tested only on x86-64.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
Changes in v2:
- Silence warning in patch #2 with architectures that don't use addr in
  their pte_clear() macro by using "(void)addr"
- Refine patch descriptions.
- Link to v1: https://lore.kernel.org/r/20260611-clear_not_present_full_ptes-v1-0-49865fc82629@kernel.org

---

David Hildenbrand (Arm) (3):
      sparc/mm: drop custom pte_clear_not_present_full()
      mm: drop pte_clear_not_present_full()
      mm: cleanup clear_not_present_full_ptes() and rename to clear_non_present_ptes()

 arch/sparc/include/asm/pgtable_64.h |  4 ----
 include/linux/pgtable.h             | 33 +++++++--------------------------
 mm/madvise.c                        |  6 +++---
 mm/memory.c                         |  2 +-
 4 files changed, 11 insertions(+), 34 deletions(-)

---

base-commit: fe61612214b618072b4ea3f5065a81296df6dd75

change-id: 20260610-clear_not_present_full_ptes-df3258baf7ed

--

Cheers,

David

[PATCH v2 1/3] sparc/mm: drop custom pte_clear_not_present_full()

[David Hildenbrand (Arm)]

On sparc64, pte_clear_not_present_full() nowadays does a simple
__set_pte_at(). In __set_pte_at() -> maybe_tlb_batch_add(), we check
pte_accessible() to see whether to call tlb_batch_add().

However, non-present PTEs are surely not accessible, so tlb_batch_add()
is never called and the "full" parameter is irrelevant.

Let's drop the helper and just let common code do a pte_clear().

pte_clear() on sparc64 maps to set_pte_at()->set_ptes()->__set_pte_at()
... so it ends up calling the same function, just with "full=0".

Given that "full" is irrelevant, there is no change.

We added pte_clear_not_present_full() for sparc64 in commit 90f08e399d05
("sparc: mmu_gather rework"), and I suspect that it was already not
required back then.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 arch/sparc/include/asm/pgtable_64.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 74ede706fb325..0837ebbc5dce6 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -945,10 +945,6 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 #define pte_clear(mm,addr,ptep)		\
 	set_pte_at((mm), (addr), (ptep), __pte(0UL))
 
-#define __HAVE_ARCH_PTE_CLEAR_NOT_PRESENT_FULL
-#define pte_clear_not_present_full(mm,addr,ptep,fullmm)	\
-	__set_pte_at((mm), (addr), (ptep), __pte(0UL), (fullmm))
-
 #ifdef DCACHE_ALIASING_POSSIBLE
 #define __HAVE_ARCH_MOVE_PTE
 #define move_pte(pte, old_addr, new_addr)				\

-- 
2.43.0

[PATCH v2 2/3] mm: drop pte_clear_not_present_full()

[David Hildenbrand (Arm)]

In general, there is no good reason to do anything special when clearing
non-present PTEs.

In theory, HW that does have to invalidate TLBs for non-present PTEs could
benefit from a "full" parameter, but fortunately
pte_clear_not_present_full() is not wired up anymore ... and there would
have to be something very convincing for us to care about that to re-add
it.

So, let's just use pte_clear() directly now. To avoid the compiler
complaining on some configs about unused "addr" parameter, silence that
here.

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 include/linux/pgtable.h | 21 ++++-----------------
 mm/madvise.c            |  4 ++--
 2 files changed, 6 insertions(+), 19 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index dc804296d78f7..0b81e396816a5 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -988,21 +988,6 @@ static inline void update_mmu_tlb(struct vm_area_struct *vma,
 	update_mmu_tlb_range(vma, address, ptep, 1);
 }
 
-/*
- * Some architectures may be able to avoid expensive synchronization
- * primitives when modifications are made to PTE's which are already
- * not present, or in the process of an address space destruction.
- */
-#ifndef __HAVE_ARCH_PTE_CLEAR_NOT_PRESENT_FULL
-static inline void pte_clear_not_present_full(struct mm_struct *mm,
-					      unsigned long address,
-					      pte_t *ptep,
-					      int full)
-{
-	pte_clear(mm, address, ptep);
-}
-#endif
-
 #ifndef clear_not_present_full_ptes
 /**
  * clear_not_present_full_ptes - Clear multiple not present PTEs which are
@@ -1014,7 +999,7 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm,
  * @full: Whether we are clearing a full mm.
  *
  * May be overridden by the architecture; otherwise, implemented as a simple
- * loop over pte_clear_not_present_full().
+ * loop over pte_clear().
  *
  * Context: The caller holds the page table lock.  The PTEs are all not present.
  * The PTEs are all in the same PMD.
@@ -1022,8 +1007,10 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm,
 static inline void clear_not_present_full_ptes(struct mm_struct *mm,
 		unsigned long addr, pte_t *ptep, unsigned int nr, int full)
 {
+	(void)addr;
+
 	for (;;) {
-		pte_clear_not_present_full(mm, addr, ptep, full);
+		pte_clear(mm, addr, ptep);
 		if (--nr == 0)
 			break;
 		ptep++;
diff --git a/mm/madvise.c b/mm/madvise.c
index cd9bb077072cc..f3cda54c1d6a0 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -698,7 +698,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 				clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm);
 			} else if (softleaf_is_hwpoison(entry) ||
 				   softleaf_is_poison_marker(entry)) {
-				pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+				pte_clear(mm, addr, pte);
 			}
 			continue;
 		}
@@ -1234,7 +1234,7 @@ static int guard_remove_pte_entry(pte_t *pte, unsigned long addr,
 
 	if (is_guard_pte_marker(ptent)) {
 		/* Simply clear the PTE marker. */
-		pte_clear_not_present_full(walk->mm, addr, pte, false);
+		pte_clear(walk->mm, addr, pte);
 		update_mmu_cache(walk->vma, addr, pte);
 	}
 

-- 
2.43.0

[PATCH v2 3/3] mm: cleanup clear_not_present_full_ptes() and rename to clear_non_present_ptes()

[David Hildenbrand (Arm)]

Let's clean it up a bit:

(1) There is no need to pass "full" anymore.

(2) No architecture overwrites it, and there isn't really a good reason
    to do so when dealing with non-resent PTEs.

(3) While at it, call it "non-present", similar to copy_nonpresent_pte()
    and zap_nonpresent_ptes().

It's a shame that we have clear_non_present_ptes() correspond to
pte_clear() and clear_ptes() correspond to ptep_get_and_clear*().

Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 include/linux/pgtable.h | 14 ++++----------
 mm/madvise.c            |  2 +-
 mm/memory.c             |  2 +-
 3 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 0b81e396816a5..d52d2a976e5a2 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -988,24 +988,19 @@ static inline void update_mmu_tlb(struct vm_area_struct *vma,
 	update_mmu_tlb_range(vma, address, ptep, 1);
 }
 
-#ifndef clear_not_present_full_ptes
 /**
- * clear_not_present_full_ptes - Clear multiple not present PTEs which are
- *				 consecutive in the pgtable.
+ * clear_nonpresent_ptes - Clear multiple non-present PTEs which are
+ *			    consecutive in the pgtable.
  * @mm: Address space the ptes represent.
  * @addr: Address of the first pte.
  * @ptep: Page table pointer for the first entry.
  * @nr: Number of entries to clear.
- * @full: Whether we are clearing a full mm.
- *
- * May be overridden by the architecture; otherwise, implemented as a simple
- * loop over pte_clear().
  *
  * Context: The caller holds the page table lock.  The PTEs are all not present.
  * The PTEs are all in the same PMD.
  */
-static inline void clear_not_present_full_ptes(struct mm_struct *mm,
-		unsigned long addr, pte_t *ptep, unsigned int nr, int full)
+static inline void clear_nonpresent_ptes(struct mm_struct *mm,
+		unsigned long addr, pte_t *ptep, unsigned int nr)
 {
 	(void)addr;
 
@@ -1017,7 +1012,6 @@ static inline void clear_not_present_full_ptes(struct mm_struct *mm,
 		addr += PAGE_SIZE;
 	}
 }
-#endif
 
 #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
 extern pte_t ptep_clear_flush(struct vm_area_struct *vma,
diff --git a/mm/madvise.c b/mm/madvise.c
index f3cda54c1d6a0..3db143c442eaa 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -695,7 +695,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 				nr = swap_pte_batch(pte, max_nr, ptent);
 				nr_swap -= nr;
 				swap_put_entries_direct(entry, nr);
-				clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm);
+				clear_nonpresent_ptes(mm, addr, pte, nr);
 			} else if (softleaf_is_hwpoison(entry) ||
 				   softleaf_is_poison_marker(entry)) {
 				pte_clear(mm, addr, pte);
diff --git a/mm/memory.c b/mm/memory.c
index ff338c2abe923..a3fcaf8cfe8f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1797,7 +1797,7 @@ static inline int zap_nonpresent_ptes(struct mmu_gather *tlb,
 		pr_alert("unrecognized swap entry 0x%lx\n", entry.val);
 		WARN_ON_ONCE(1);
 	}
-	clear_not_present_full_ptes(vma->vm_mm, addr, pte, nr, tlb->fullmm);
+	clear_nonpresent_ptes(vma->vm_mm, addr, pte, nr);
 	*any_skipped = zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent);
 
 	return nr;

-- 
2.43.0

Re: [PATCH v2 2/3] mm: drop pte_clear_not_present_full()

[Andrew Morton]

On Mon, 29 Jun 2026 15:49:48 +0200 "David Hildenbrand (Arm)" <david@kernel.org> wrote:

> In general, there is no good reason to do anything special when clearing
> non-present PTEs.
> 
> In theory, HW that does have to invalidate TLBs for non-present PTEs could
> benefit from a "full" parameter, but fortunately
> pte_clear_not_present_full() is not wired up anymore ... and there would
> have to be something very convincing for us to care about that to re-add
> it.
> 
> So, let's just use pte_clear() directly now. To avoid the compiler
> complaining on some configs about unused "addr" parameter, silence that
> here.

Wait, which configs do that?

> @@ -1022,8 +1007,10 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm,
>  static inline void clear_not_present_full_ptes(struct mm_struct *mm,
>  		unsigned long addr, pte_t *ptep, unsigned int nr, int full)
>  {
> +	(void)addr;
> +

We heavily rely on this warning not happening.

eg, one of thousands:

static inline bool page_range_contiguous(const struct page *page,
		unsigned long nr_pages)
{
	return true;
}

So... what's happening here?

Re: [PATCH v2 2/3] mm: drop pte_clear_not_present_full()

[David Hildenbrand (Arm)]

On 6/29/26 19:22, Andrew Morton wrote:
> On Mon, 29 Jun 2026 15:49:48 +0200 "David Hildenbrand (Arm)" <david@kernel.org> wrote:
> 
>> In general, there is no good reason to do anything special when clearing
>> non-present PTEs.
>>
>> In theory, HW that does have to invalidate TLBs for non-present PTEs could
>> benefit from a "full" parameter, but fortunately
>> pte_clear_not_present_full() is not wired up anymore ... and there would
>> have to be something very convincing for us to care about that to re-add
>> it.
>>
>> So, let's just use pte_clear() directly now. To avoid the compiler
>> complaining on some configs about unused "addr" parameter, silence that
>> here.
> 
> Wait, which configs do that?
> 
>> @@ -1022,8 +1007,10 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm,
>>  static inline void clear_not_present_full_ptes(struct mm_struct *mm,
>>  		unsigned long addr, pte_t *ptep, unsigned int nr, int full)
>>  {
>> +	(void)addr;
>> +
> 
> We heavily rely on this warning not happening.
> 
> eg, one of thousands:
> 
> static inline bool page_range_contiguous(const struct page *page,
> 		unsigned long nr_pages)
> {
> 	return true;
> }
> 
> So... what's happening here?

"nr_pages" are not modified in the function, so the compile does not complain.
See below.


A private build bot barked at me after v1 for

	arm-linux-gnueabi-gcc
	openrisc-allnoconfig
	um-allmodconfig

For example:

https://lore.kernel.org/all/202606121420.Wke8Ipgx-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from include/linux/kasan.h:38,
                    from include/linux/slab.h:264,
                    from lib/test_bitops.c:12:
   include/linux/pgtable.h: In function 'clear_not_present_full_ptes':
>> include/linux/pgtable.h:974:31: error: parameter 'addr' set but not used
[-Werror=unused-but-set-parameter=]
     974 |                 unsigned long addr, pte_t *ptep, unsigned int nr, int
full)
         |                 ~~~~~~~~~~~~~~^~~~
   cc1: all warnings being treated as errors


The problem is that addr is updated (written) in the function but never read.
This becomes visible once pte_clear() is a macro instead of a function.

	arch/arm/include/asm/pgtable.h:#define pte_clear(mm,addr,ptep)
set_pte_ext(ptep, __pte(0), 0)


"(void) addr" silences bots. An alternative would be to find all such macros and
convert them into (assuming inline function is non-trivial)

#define pte_clear(mm,addr,ptep)  ((void)addr, set_pte_ext(ptep, __pte(0), 0))

Something I wanted to avoid for this simple patch here that just removes one
function indirection.

-- 
Cheers,

David

Re: [PATCH v2 2/3] mm: drop pte_clear_not_present_full()

[Andrew Morton]

On Mon, 29 Jun 2026 19:43:53 +0200 "David Hildenbrand (Arm)" <david@kernel.org> wrote:

> > So... what's happening here?
> 
> "nr_pages" are not modified in the function, so the compile does not complain.
> See below.
> 
> 
> A private build bot barked at me after v1 for
> 
> 	arm-linux-gnueabi-gcc
> 	openrisc-allnoconfig
> 	um-allmodconfig
> 
> For example:
> 
> https://lore.kernel.org/all/202606121420.Wke8Ipgx-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from include/linux/kasan.h:38,
>                     from include/linux/slab.h:264,
>                     from lib/test_bitops.c:12:
>    include/linux/pgtable.h: In function 'clear_not_present_full_ptes':
> >> include/linux/pgtable.h:974:31: error: parameter 'addr' set but not used
> [-Werror=unused-but-set-parameter=]
>      974 |                 unsigned long addr, pte_t *ptep, unsigned int nr, int
> full)
>          |                 ~~~~~~~~~~~~~~^~~~
>    cc1: all warnings being treated as errors
> 
> 
> The problem is that addr is updated (written) in the function but never read.

Oh, OK, thanks.  I altered the changelog to read

"To prevent the compiler complaining on some configs about "set but not
used" addr parameter, silence that here."

Re: [PATCH v2 1/3] sparc/mm: drop custom pte_clear_not_present_full()

[Lance Yang]

On Mon, Jun 29, 2026 at 03:49:47PM +0200, David Hildenbrand (Arm) wrote:
>On sparc64, pte_clear_not_present_full() nowadays does a simple
>__set_pte_at(). In __set_pte_at() -> maybe_tlb_batch_add(), we check
>pte_accessible() to see whether to call tlb_batch_add().
>
>However, non-present PTEs are surely not accessible, so tlb_batch_add()
>is never called and the "full" parameter is irrelevant.
>
>Let's drop the helper and just let common code do a pte_clear().
>
>pte_clear() on sparc64 maps to set_pte_at()->set_ptes()->__set_pte_at()
>... so it ends up calling the same function, just with "full=0".
>
>Given that "full" is irrelevant, there is no change.
>
>We added pte_clear_not_present_full() for sparc64 in commit 90f08e399d05
>("sparc: mmu_gather rework"), and I suspect that it was already not
>required back then.
>
>Cc: Peter Zijlstra <peterz@infradead.org>
>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>---

fullmm only matters if an old non-present PTE can pass pte_accessible().
IIUC, that doesn't happen on sparc64 :)

LGTM. Feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>

Re: [PATCH v2 2/3] mm: drop pte_clear_not_present_full()

[Lance Yang]

On Mon, Jun 29, 2026 at 03:49:48PM +0200, David Hildenbrand (Arm) wrote:
>In general, there is no good reason to do anything special when clearing
>non-present PTEs.
>
>In theory, HW that does have to invalidate TLBs for non-present PTEs could
>benefit from a "full" parameter, but fortunately
>pte_clear_not_present_full() is not wired up anymore ... and there would
>have to be something very convincing for us to care about that to re-add
>it.
>
>So, let's just use pte_clear() directly now. To avoid the compiler
>complaining on some configs about unused "addr" parameter, silence that
>here.
>
>Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>---

With the sparc64 override gone, pte_clear_not_present_full() is just
pte_clear() :)

LGTM. Feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>

Re: [PATCH v2 3/3] mm: cleanup clear_not_present_full_ptes() and rename to clear_non_present_ptes()

[Lance Yang]

On Mon, Jun 29, 2026 at 03:49:49PM +0200, David Hildenbrand (Arm) wrote:
>Let's clean it up a bit:
>
>(1) There is no need to pass "full" anymore.
>
>(2) No architecture overwrites it, and there isn't really a good reason
>    to do so when dealing with non-resent PTEs.

Nit: "non-resent PTEs" -> "non-present PTEs".

>
>(3) While at it, call it "non-present", similar to copy_nonpresent_pte()
>    and zap_nonpresent_ptes().
>
>It's a shame that we have clear_non_present_ptes() correspond to
>pte_clear() and clear_ptes() correspond to ptep_get_and_clear*().
>
>Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>---

Nice cleanup! Feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>

Re: [PATCH v2 3/3] mm: cleanup clear_not_present_full_ptes() and rename to clear_non_present_ptes()

[David Hildenbrand (Arm)]

On 6/30/26 15:05, Lance Yang wrote:
> 
> On Mon, Jun 29, 2026 at 03:49:49PM +0200, David Hildenbrand (Arm) wrote:
>> Let's clean it up a bit:
>>
>> (1) There is no need to pass "full" anymore.
>>
>> (2) No architecture overwrites it, and there isn't really a good reason
>>    to do so when dealing with non-resent PTEs.
> 
> Nit: "non-resent PTEs" -> "non-present PTEs".

Thanks, maybe Andrew can clean that up? Thanks!

-- 
Cheers,

David