__zap_vma_range() has two callers, whereby
zap_page_range_single_batched() documents that the range must fit into
the VMA range.

So move adjusting the range to unmap_vmas() where it is actually
required and add a safety check in __zap_vma_range() instead. In
unmap_vmas(), we'd never expect to have empty ranges (otherwise, why
have the vma in there in the first place).

__zap_vma_range() will no longer be called with start == end, so
cleanup the function a bit. While at it, simplify the overly long
comment to its core message.

We will no longer call uprobe_munmap() for start == end, which actually
seems to be the right thing to do.

Note that hugetlb_zap_begin()->...->adjust_range_if_pmd_sharing_possible()
cannot result in the range exceeding the vma range.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/memory.c | 58 +++++++++++++++++++++--------------------------------
 1 file changed, 23 insertions(+), 35 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f0aaec57a66b..fdcd2abf29c2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2073,44 +2073,28 @@ static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	tlb_end_vma(tlb, vma);
 }
 
-
-static void __zap_vma_range(struct mmu_gather *tlb,
-		struct vm_area_struct *vma, unsigned long start_addr,
-		unsigned long end_addr, struct zap_details *details)
+static void __zap_vma_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		unsigned long start, unsigned long end,
+		struct zap_details *details)
 {
-	unsigned long start = max(vma->vm_start, start_addr);
-	unsigned long end;
-
-	if (start >= vma->vm_end)
-		return;
-	end = min(vma->vm_end, end_addr);
-	if (end <= vma->vm_start)
-		return;
+	VM_WARN_ON_ONCE(start >= end || !range_in_vma(vma, start, end));
 
 	if (vma->vm_file)
 		uprobe_munmap(vma, start, end);
 
-	if (start != end) {
-		if (unlikely(is_vm_hugetlb_page(vma))) {
-			/*
-			 * It is undesirable to test vma->vm_file as it
-			 * should be non-null for valid hugetlb area.
-			 * However, vm_file will be NULL in the error
-			 * cleanup path of mmap_region. When
-			 * hugetlbfs ->mmap method fails,
-			 * mmap_region() nullifies vma->vm_file
-			 * before calling this function to clean up.
-			 * Since no pte has actually been setup, it is
-			 * safe to do nothing in this case.
-			 */
-			if (vma->vm_file) {
-				zap_flags_t zap_flags = details ?
-				    details->zap_flags : 0;
-				__unmap_hugepage_range(tlb, vma, start, end,
-							     NULL, zap_flags);
-			}
-		} else
-			unmap_page_range(tlb, vma, start, end, details);
+	if (unlikely(is_vm_hugetlb_page(vma))) {
+		zap_flags_t zap_flags = details ? details->zap_flags : 0;
+
+		/*
+		 * vm_file will be NULL when we fail early while instantiating
+		 * a new mapping. In this case, no pages were mapped yet and
+		 * there is nothing to do.
+		 */
+		if (!vma->vm_file)
+			return;
+		__unmap_hugepage_range(tlb, vma, start, end, NULL, zap_flags);
+	} else {
+		unmap_page_range(tlb, vma, start, end, details);
 	}
 }
 
@@ -2174,8 +2158,9 @@ void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap)
 				unmap->vma_start, unmap->vma_end);
 	mmu_notifier_invalidate_range_start(&range);
 	do {
-		unsigned long start = unmap->vma_start;
-		unsigned long end = unmap->vma_end;
+		unsigned long start = max(vma->vm_start, unmap->vma_start);
+		unsigned long end = min(vma->vm_end, unmap->vma_end);
+
 		hugetlb_zap_begin(vma, &start, &end);
 		__zap_vma_range(tlb, vma, start, end, &details);
 		hugetlb_zap_end(vma, &details);
@@ -2204,6 +2189,9 @@ void zap_page_range_single_batched(struct mmu_gather *tlb,
 
 	VM_WARN_ON_ONCE(!tlb || tlb->mm != vma->vm_mm);
 
+	if (unlikely(!size))
+		return;
+
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
 				address, end);
 	hugetlb_zap_begin(vma, &range.start, &range.end);
-- 
2.43.0