Re: [PATCH 6/6] mm: change to return bool for the MMU notifier's young flag check

From: "Lorenzo Stoakes (Oracle)" <ljs@kernel.org>
Date: 2026-03-19 11:39:49
Also in: kvm, linux-mm, linux-riscv, linux-s390, linuxppc-dev, lkml

On Thu, Mar 19, 2026 at 11:24:05AM +0800, Baolin Wang wrote:

The MMU notifier young flag check related functions only return whether
the young flag was set. Change the return type to bool to make the
intention clearer.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

I can see KVM is the only user for the mmu_notifier_ops clear_flush_young,
clear_young and test_young hooks, which map to
kvm_mmu_notifier_[clear_flush,clear,test]_young() functions, and you have
updated them all.

So this LGTM with nits below, and so (with nits addressed as per the other R-b
tags :):

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Thanks for doing this! Int as bool is a pet peeve of mine :))

Cheers, Lorenzo

quoted hunk ↗ jump to hunk

---
 include/linux/mmu_notifier.h | 76 +++++++++++++++++-------------------
 mm/internal.h                | 16 ++++----
 mm/mmu_notifier.c            | 20 +++++-----
 virt/kvm/kvm_main.c          | 40 +++++++++----------
 4 files changed, 72 insertions(+), 80 deletions(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 3705d350c863..17f2cdc77dd5 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h

@@ -97,20 +97,20 @@ struct mmu_notifier_ops {
 	 * Start-end is necessary in case the secondary MMU is mapping the page
 	 * at a smaller granularity than the primary MMU.
 	 */
-	int (*clear_flush_young)(struct mmu_notifier *subscription,
-				 struct mm_struct *mm,
-				 unsigned long start,
-				 unsigned long end);
+	bool (*clear_flush_young)(struct mmu_notifier *subscription,
+				  struct mm_struct *mm,
+				  unsigned long start,
+				  unsigned long end);

 	/*
 	 * clear_young is a lightweight version of clear_flush_young. Like the
 	 * latter, it is supposed to test-and-clear the young/accessed bitflag
 	 * in the secondary pte, but it may omit flushing the secondary tlb.
 	 */
-	int (*clear_young)(struct mmu_notifier *subscription,
-			   struct mm_struct *mm,
-			   unsigned long start,
-			   unsigned long end);
+	bool (*clear_young)(struct mmu_notifier *subscription,
+			    struct mm_struct *mm,
+			    unsigned long start,
+			    unsigned long end);

 	/*
 	 * test_young is called to check the young/accessed bitflag in

@@ -118,9 +118,9 @@ struct mmu_notifier_ops {
 	 * frequently used without actually clearing the flag or tearing
 	 * down the secondary mapping on the page.
 	 */
-	int (*test_young)(struct mmu_notifier *subscription,
-			  struct mm_struct *mm,
-			  unsigned long address);
+	bool (*test_young)(struct mmu_notifier *subscription,
+			   struct mm_struct *mm,
+			   unsigned long address);

 	/*
 	 * invalidate_range_start() and invalidate_range_end() must be

@@ -376,14 +376,12 @@ mmu_interval_check_retry(struct mmu_interval_notifier *interval_sub,

 extern void __mmu_notifier_subscriptions_destroy(struct mm_struct *mm);
 extern void __mmu_notifier_release(struct mm_struct *mm);
-extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
-					  unsigned long start,
-					  unsigned long end);
-extern int __mmu_notifier_clear_young(struct mm_struct *mm,
-				      unsigned long start,
-				      unsigned long end);
-extern int __mmu_notifier_test_young(struct mm_struct *mm,
-				     unsigned long address);
+bool __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end);
+bool __mmu_notifier_clear_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end);
+bool __mmu_notifier_test_young(struct mm_struct *mm,
+		unsigned long address);
 extern int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *r);
 extern void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *r);
 extern void __mmu_notifier_arch_invalidate_secondary_tlbs(struct mm_struct *mm,

I mean damn, at this point maybe it's legit to drop the surrounding externs here
too? But maybe not :))

quoted hunk ↗ jump to hunk

@@ -403,30 +401,28 @@ static inline void mmu_notifier_release(struct mm_struct *mm)
 		__mmu_notifier_release(mm);
 }

-static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
-					  unsigned long start,
-					  unsigned long end)
+static inline bool mmu_notifier_clear_flush_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
 	if (mm_has_notifiers(mm))
 		return __mmu_notifier_clear_flush_young(mm, start, end);
-	return 0;
+	return false;
 }

-static inline int mmu_notifier_clear_young(struct mm_struct *mm,
-					   unsigned long start,
-					   unsigned long end)
+static inline bool mmu_notifier_clear_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
 	if (mm_has_notifiers(mm))
 		return __mmu_notifier_clear_young(mm, start, end);
-	return 0;
+	return false;
 }

-static inline int mmu_notifier_test_young(struct mm_struct *mm,
-					  unsigned long address)
+static inline bool mmu_notifier_test_young(struct mm_struct *mm,
+		unsigned long address)
 {
 	if (mm_has_notifiers(mm))
 		return __mmu_notifier_test_young(mm, address);
-	return 0;
+	return false;
 }

 static inline void

@@ -552,24 +548,22 @@ static inline void mmu_notifier_release(struct mm_struct *mm)
 {
 }

-static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
-					  unsigned long start,
-					  unsigned long end)
+static inline bool mmu_notifier_clear_flush_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
-	return 0;
+	return false;
 }

-static inline int mmu_notifier_clear_young(struct mm_struct *mm,
-					   unsigned long start,
-					   unsigned long end)
+static inline bool mmu_notifier_clear_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
-	return 0;
+	return false;
 }

-static inline int mmu_notifier_test_young(struct mm_struct *mm,
-					  unsigned long address)
+static inline bool mmu_notifier_test_young(struct mm_struct *mm,
+		unsigned long address)
 {
-	return 0;
+	return false;
 }

 static inline void

diff --git a/mm/internal.h b/mm/internal.h
index 0eaca2f0eb6a..3d6eba216364 100644
--- a/mm/internal.h
+++ b/mm/internal.h

@@ -1831,10 +1831,10 @@ static inline int io_remap_pfn_range_complete(struct vm_area_struct *vma,
 }

 #ifdef CONFIG_MMU_NOTIFIER
-static inline int clear_flush_young_ptes_notify(struct vm_area_struct *vma,
+static inline bool clear_flush_young_ptes_notify(struct vm_area_struct *vma,
 		unsigned long addr, pte_t *ptep, unsigned int nr)
 {
-	int young;
+	bool young;

 	young = clear_flush_young_ptes(vma, addr, ptep, nr);
 	young |= mmu_notifier_clear_flush_young(vma->vm_mm, addr,

@@ -1842,30 +1842,30 @@ static inline int clear_flush_young_ptes_notify(struct vm_area_struct *vma,
 	return young;
 }

-static inline int pmdp_clear_flush_young_notify(struct vm_area_struct *vma,
+static inline bool pmdp_clear_flush_young_notify(struct vm_area_struct *vma,
 		unsigned long addr, pmd_t *pmdp)
 {
-	int young;
+	bool young;

 	young = pmdp_clear_flush_young(vma, addr, pmdp);
 	young |= mmu_notifier_clear_flush_young(vma->vm_mm, addr, addr + PMD_SIZE);
 	return young;
 }

-static inline int test_and_clear_young_ptes_notify(struct vm_area_struct *vma,
+static inline bool test_and_clear_young_ptes_notify(struct vm_area_struct *vma,
 		unsigned long addr, pte_t *ptep, unsigned int nr)
 {
-	int young;
+	bool young;

 	young = test_and_clear_young_ptes(vma, addr, ptep, nr);
 	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + nr * PAGE_SIZE);
 	return young;
 }

-static inline int pmdp_test_and_clear_young_notify(struct vm_area_struct *vma,
+static inline bool pmdp_test_and_clear_young_notify(struct vm_area_struct *vma,
 		unsigned long addr, pmd_t *pmdp)
 {
-	int young;
+	bool young;

 	young = pmdp_test_and_clear_young(vma, addr, pmdp);
 	young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PMD_SIZE);

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 2502474b83b6..3e3e7e727ba2 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c

@@ -364,12 +364,11 @@ void __mmu_notifier_release(struct mm_struct *mm)
  * unmap the address and return 1 or 0 depending if the mapping previously
  * existed or not.
  */
-int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
-					unsigned long start,
-					unsigned long end)
+bool __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
 	struct mmu_notifier *subscription;
-	int young = 0, id;
+	bool young = false, id;

 	id = srcu_read_lock(&srcu);
 	hlist_for_each_entry_srcu(subscription,

@@ -384,12 +383,11 @@ int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
 	return young;
 }

-int __mmu_notifier_clear_young(struct mm_struct *mm,
-			       unsigned long start,
-			       unsigned long end)
+bool __mmu_notifier_clear_young(struct mm_struct *mm,
+		unsigned long start, unsigned long end)
 {
 	struct mmu_notifier *subscription;
-	int young = 0, id;
+	bool young = false, id;

 	id = srcu_read_lock(&srcu);
 	hlist_for_each_entry_srcu(subscription,

@@ -404,11 +402,11 @@ int __mmu_notifier_clear_young(struct mm_struct *mm,
 	return young;
 }

-int __mmu_notifier_test_young(struct mm_struct *mm,
-			      unsigned long address)
+bool __mmu_notifier_test_young(struct mm_struct *mm,
+		unsigned long address)
 {
 	struct mmu_notifier *subscription;
-	int young = 0, id;
+	bool young = false, id;

 	id = srcu_read_lock(&srcu);
 	hlist_for_each_entry_srcu(subscription,

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d0ab29672c71..6bcfc1b3021d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c

@@ -646,11 +646,11 @@ static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm,
 	return r;
 }

-static __always_inline int kvm_age_hva_range(struct mmu_notifier *mn,
-						unsigned long start,
-						unsigned long end,
-						gfn_handler_t handler,
-						bool flush_on_ret)
+static __always_inline bool kvm_age_hva_range(struct mmu_notifier *mn,
+					      unsigned long start,
+					      unsigned long end,
+					      gfn_handler_t handler,
+					      bool flush_on_ret)

Can we please fix this terrrible indentation while we're here :)?

static __always_inline bool kvm_age_hva_range(struct mmu_notifier *mn,
		unsigned long start, unsigned long end, gfn_handler_t handler,
		bool flush_on_ret)

Would be nicer, thanks!

quoted hunk ↗ jump to hunk

 {
 	struct kvm *kvm = mmu_notifier_to_kvm(mn);
 	const struct kvm_mmu_notifier_range range = {

@@ -666,10 +666,10 @@ static __always_inline int kvm_age_hva_range(struct mmu_notifier *mn,
 	return kvm_handle_hva_range(kvm, &range).ret;
 }

-static __always_inline int kvm_age_hva_range_no_flush(struct mmu_notifier *mn,
-						      unsigned long start,
-						      unsigned long end,
-						      gfn_handler_t handler)
+static __always_inline bool kvm_age_hva_range_no_flush(struct mmu_notifier *mn,
+						       unsigned long start,
+						       unsigned long end,
+						       gfn_handler_t handler)

Same indentation comment here.

quoted hunk ↗ jump to hunk

 {
 	return kvm_age_hva_range(mn, start, end, handler, false);
 }

@@ -829,10 +829,10 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
 		rcuwait_wake_up(&kvm->mn_memslots_update_rcuwait);
 }

-static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
-					      struct mm_struct *mm,
-					      unsigned long start,
-					      unsigned long end)
+static bool kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
+					       struct mm_struct *mm,
+					       unsigned long start,
+					       unsigned long end)

Same indentation comment here.

quoted hunk ↗ jump to hunk

 {
 	trace_kvm_age_hva(start, end);

@@ -840,10 +840,10 @@ static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
 				 !IS_ENABLED(CONFIG_KVM_ELIDE_TLB_FLUSH_IF_YOUNG));
 }

-static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
-					struct mm_struct *mm,
-					unsigned long start,
-					unsigned long end)
+static bool kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
+					 struct mm_struct *mm,
+					 unsigned long start,
+					 unsigned long end)

Same indentation comment here.

quoted hunk ↗ jump to hunk

 {
 	trace_kvm_age_hva(start, end);

@@ -863,9 +863,9 @@ static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
 	return kvm_age_hva_range_no_flush(mn, start, end, kvm_age_gfn);
 }

-static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
-				       struct mm_struct *mm,
-				       unsigned long address)
+static bool kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
+					struct mm_struct *mm,
+					unsigned long address)

Same indentation comment here.

 {
 	trace_kvm_test_age_hva(address);

--
2.47.3

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