[PATCH v1 01/16] mm/madvise: drop range checks in madvise_free_single_vma()

["David Hildenbrand (Arm)" <david@kernel.org>]

madvise_vma_behavior()-> madvise_dontneed_free()->madvise_free_single_vma()
is only called from madvise_walk_vmas()

(a) After try_vma_read_lock() confirmed that the whole range falls into
    a single VMA (see is_vma_lock_sufficient()).

(b) After adjusting the range to the VMA in the loop afterwards.

madvise_dontneed_free() might drop the MM lock when handling
userfaultfd, but it properly looks up the VMA again to adjust the range.

So in madvise_free_single_vma(), the given range should always fall into
a single VMA and should also span at least one page.

Let's drop the error checks.

The code now matches what we do in madvise_dontneed_single_vma(), where
we call zap_vma_range_batched() that documents: "The range must fit into
one VMA.". Although that function still adjusts that range, we'll change
that soon.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/madvise.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index c0370d9b4e23..efc04334a000 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -799,9 +799,10 @@ static int madvise_free_single_vma(struct madvise_behavior *madv_behavior)
 {
 	struct mm_struct *mm = madv_behavior->mm;
 	struct vm_area_struct *vma = madv_behavior->vma;
-	unsigned long start_addr = madv_behavior->range.start;
-	unsigned long end_addr = madv_behavior->range.end;
-	struct mmu_notifier_range range;
+	struct mmu_notifier_range range = {
+		.start = madv_behavior->range.start,
+		.end = madv_behavior->range.end,
+	};
 	struct mmu_gather *tlb = madv_behavior->tlb;
 	struct mm_walk_ops walk_ops = {
 		.pmd_entry		= madvise_free_pte_range,
@@ -811,12 +812,6 @@ static int madvise_free_single_vma(struct madvise_behavior *madv_behavior)
 	if (!vma_is_anonymous(vma))
 		return -EINVAL;
 
-	range.start = max(vma->vm_start, start_addr);
-	if (range.start >= vma->vm_end)
-		return -EINVAL;
-	range.end = min(vma->vm_end, end_addr);
-	if (range.end <= vma->vm_start)
-		return -EINVAL;
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
 				range.start, range.end);
 
-- 
2.43.0