[PATCH v1 4/9] mm/memory: Add tree limit to free_pgtables()

[Liam R. Howlett]

The ceiling and tree search limit need to be different arguments for the
future change in the failed fork attempt.

Add some documentation around free_pgtables() and the limits in an
attempt to clarify the floor and ceiling use as well as the new
tree_max.

Test code also updated.

No functional changes intended.

Signed-off-by: Liam R. Howlett <Liam.Howlett at oracle.com>
---
 mm/internal.h                    |  4 +++-
 mm/memory.c                      | 28 +++++++++++++++++++++++++---
 mm/mmap.c                        |  2 +-
 mm/vma.c                         |  3 ++-
 tools/testing/vma/vma_internal.h |  3 ++-
 5 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 63e3ec8d63be7..d295252407fee 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -444,7 +444,9 @@ void folio_activate(struct folio *folio);
 
 void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
 		   struct vm_area_struct *start_vma, unsigned long floor,
-		   unsigned long ceiling, bool mm_wr_locked);
+		   unsigned long ceiling, unsigned long tree_max,
+		   bool mm_wr_locked);
+
 void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte);
 
 struct zap_details;
diff --git a/mm/memory.c b/mm/memory.c
index 3e0404bd57a02..24716b3713f66 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -369,12 +369,34 @@ void free_pgd_range(struct mmu_gather *tlb,
 	} while (pgd++, addr = next, addr != end);
 }
 
+/*
+ * free_pgtables() - Free a range of page tables
+ * @tlb: The mmu gather
+ * @mas: The maple state
+ * @vma: The first vma
+ * @floor: The lowest page table address
+ * @ceiling: The highest page table address
+ * @tree_max: The highest tree search address
+ * @mm_wr_locked: boolean indicating if the mm is write locked
+ *
+ * Note: Floor and ceiling are provided to indicate the absolute range of the
+ * page tables that should be removed.  This can differ from the vma mappings on
+ * some archs that may have mappings that need to be removed outside the vmas.
+ * Note that the prev->vm_end and next->vm_start are often used.
+ *
+ * The tree_max differs from the ceiling when a dup_mmap() failed and the tree
+ * has unrelated data to the mm_struct being torn down.
+ */
 void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
 		   struct vm_area_struct *vma, unsigned long floor,
-		   unsigned long ceiling, bool mm_wr_locked)
+		   unsigned long ceiling, unsigned long tree_max,
+		   bool mm_wr_locked)
 {
 	struct unlink_vma_file_batch vb;
 
+	/* underflow can happen and is fine */
+	WARN_ON_ONCE(tree_max - 1 > ceiling - 1);
+
 	tlb_free_vmas(tlb);
 
 	do {
@@ -385,7 +407,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
 		 * Note: USER_PGTABLES_CEILING may be passed as ceiling and may
 		 * be 0.  This will underflow and is okay.
 		 */
-		next = mas_find(mas, ceiling - 1);
+		next = mas_find(mas, tree_max - 1);
 		if (unlikely(xa_is_zero(next)))
 			next = NULL;
 
@@ -405,7 +427,7 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
 		 */
 		while (next && next->vm_start <= vma->vm_end + PMD_SIZE) {
 			vma = next;
-			next = mas_find(mas, ceiling - 1);
+			next = mas_find(mas, tree_max - 1);
 			if (unlikely(xa_is_zero(next)))
 				next = NULL;
 			if (mm_wr_locked)
diff --git a/mm/mmap.c b/mm/mmap.c
index a290448a53bb2..0f4808f135fe6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1311,7 +1311,7 @@ void exit_mmap(struct mm_struct *mm)
 	mt_clear_in_rcu(&mm->mm_mt);
 	vma_iter_set(&vmi, vma->vm_end);
 	free_pgtables(&tlb, &vmi.mas, vma, FIRST_USER_ADDRESS,
-		      USER_PGTABLES_CEILING, true);
+		      USER_PGTABLES_CEILING, USER_PGTABLES_CEILING, true);
 	tlb_finish_mmu(&tlb);
 
 	/*
diff --git a/mm/vma.c b/mm/vma.c
index a648e0555c873..1bae142bbc0f1 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -486,6 +486,7 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
 		   /* mm_wr_locked = */ true);
 	mas_set(mas, vma->vm_end);
 	free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
+		      next ? next->vm_start : USER_PGTABLES_CEILING,
 		      next ? next->vm_start : USER_PGTABLES_CEILING,
 		      /* mm_wr_locked = */ true);
 	tlb_finish_mmu(&tlb);
@@ -1232,7 +1233,7 @@ static inline void vms_clear_ptes(struct vma_munmap_struct *vms,
 	mas_set(mas_detach, 1);
 	/* start and end may be different if there is no prev or next vma. */
 	free_pgtables(&tlb, mas_detach, vms->vma, vms->unmap_start,
-		      vms->unmap_end, mm_wr_locked);
+		      vms->unmap_end, vms->unmap_end, mm_wr_locked);
 	tlb_finish_mmu(&tlb);
 	vms->clear_ptes = false;
 }
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 07167446dcf42..823d379e1fac2 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -900,7 +900,8 @@ static inline void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
 
 static inline void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
 		   struct vm_area_struct *vma, unsigned long floor,
-		   unsigned long ceiling, bool mm_wr_locked)
+		   unsigned long ceiling, unsigned long tree_max,
+		   bool mm_wr_locked)
 {
 	(void)tlb;
 	(void)mas;
-- 
2.47.2