mm/vma: update vma_shrink() to not pass start, pgoff parameters

vma_shrink() is only used by relocate_vma_down() to shrink the tail of a
VMA. Therefore neither the start nor the pgoff parameters make any sense.

It seemed we were passing the pgoff parameter solely to satisfy
vma_set_range()'s requirement for pgoff being specified.

Since vma_set_range() is now isolated to vma.c, we can simply introduce
__vma_set_range() which sets only vma->vm_[start, end], and invoke this
instead, removing start and pgoff from vma_shrink() altogether.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-26-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vma.c

@@ -70,11 +70,17 @@ struct mmap_state {
 		.state = VMA_MERGE_START,				\
 	}
 
-static void vma_set_range(struct vm_area_struct *vma, unsigned long start,
-			  unsigned long end, pgoff_t pgoff)
+static void __vma_set_range(struct vm_area_struct *vma, unsigned long start,
+			    unsigned long end)
 {
 	vma->vm_start = start;
 	vma->vm_end = end;
+}
+
+static void vma_set_range(struct vm_area_struct *vma, unsigned long start,
+			  unsigned long end, pgoff_t pgoff)
+{
+	__vma_set_range(vma, start, end);
 	vma->vm_pgoff = pgoff;
 }
 
@@ -1279,27 +1285,24 @@ int vma_expand(struct vma_merge_struct *vmg)
 	return -ENOMEM;
 }
 
-/*
- * vma_shrink() - Reduce an existing VMAs memory area
+/**
+ * vma_shrink() - Shrink the end of a VMA
  * @vmi: The vma iterator
  * @vma: The VMA to modify
- * @start: The new start
  * @end: The new end
  *
+ * Note that the caller may only shrink the end of the VMA.
+ *
  * Returns: 0 on success, -ENOMEM otherwise
  */
 int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
-	       unsigned long start, unsigned long end, pgoff_t pgoff)
+	       unsigned long end)
 {
 	struct vma_prepare vp;
 
-	WARN_ON((vma->vm_start != start) && (vma->vm_end != end));
-
-	if (vma->vm_start < start)
-		vma_iter_config(vmi, vma->vm_start, start);
-	else
-		vma_iter_config(vmi, end, vma->vm_end);
+	VM_WARN_ON_ONCE(end > vma->vm_end);
 
+	vma_iter_config(vmi, end, vma->vm_end);
 	if (vma_iter_prealloc(vmi, NULL))
 		return -ENOMEM;
 
@@ -1307,10 +1310,10 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 
 	init_vma_prep(&vp, vma);
 	vma_prepare(&vp);
-	vma_adjust_trans_huge(vma, start, end, NULL);
+	vma_adjust_trans_huge(vma, vma->vm_start, end, NULL);
 
 	vma_iter_clear(vmi);
-	vma_set_range(vma, start, end, pgoff);
+	__vma_set_range(vma, vma->vm_start, end);
 	vma_complete(&vp, vmi, vma->vm_mm);
 	validate_mm(vma->vm_mm);
 	return 0;

mm/vma.h

@@ -297,8 +297,7 @@ void validate_mm(struct mm_struct *mm);
 
 __must_check int vma_expand(struct vma_merge_struct *vmg);
 __must_check int vma_shrink(struct vma_iterator *vmi,
-		struct vm_area_struct *vma,
-		unsigned long start, unsigned long end, pgoff_t pgoff);
+		struct vm_area_struct *vma, unsigned long end);
 
 static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
 			struct vm_area_struct *vma, gfp_t gfp)

mm/vma_exec.c

@@ -89,7 +89,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
 
 	vma_prev(&vmi);
 	/* Shrink the vma to just the new range */
-	return vma_shrink(&vmi, vma, new_start, new_end, vma_start_pgoff(vma));
+	return vma_shrink(&vmi, vma, new_end);
 }
 
 /*

tools/testing/vma/tests/merge.c

@@ -227,7 +227,7 @@ static bool test_simple_shrink(void)
 
 	ASSERT_FALSE(attach_vma(&mm, vma));
 
-	ASSERT_FALSE(vma_shrink(&vmi, vma, 0, 0x1000, 0));
+	ASSERT_FALSE(vma_shrink(&vmi, vma, 0x1000));
 
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x1000);