[PATCH v6 7/9] binder: use per-vma lock in page installation

[Carlos Llamas]

Use per-vma locking for concurrent page installations, this minimizes
contention with unrelated vmas improving performance. The mmap_lock is
still acquired when needed though, e.g. before get_user_pages_remote().

Many thanks to Barry Song who posted a similar approach [1].

Link: https://lore.kernel.org/all/20240902225009.34576-1-21cnbao@xxxxxxxxx/ [1]
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Barry Song <v-songbaohua@xxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
---
 drivers/android/binder_alloc.c | 67 +++++++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 17 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index ce2bdf278b82..0c54e50841c8 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -233,6 +233,53 @@ static inline bool binder_alloc_is_mapped(struct binder_alloc *alloc)
 	return smp_load_acquire(&alloc->mapped);
 }
 
+static struct page *binder_page_lookup(struct binder_alloc *alloc,
+				       unsigned long addr)
+{
+	struct mm_struct *mm = alloc->mm;
+	struct page *page;
+	long npages = 0;
+
+	/*
+	 * Find an existing page in the remote mm. If missing,
+	 * don't attempt to fault-in just propagate an error.
+	 */
+	mmap_read_lock(mm);
+	if (binder_alloc_is_mapped(alloc))
+		npages = get_user_pages_remote(mm, addr, 1, FOLL_NOFAULT,
+					       &page, NULL);
+	mmap_read_unlock(mm);
+
+	return npages > 0 ? page : NULL;
+}
+
+static int binder_page_insert(struct binder_alloc *alloc,
+			      unsigned long addr,
+			      struct page *page)
+{
+	struct mm_struct *mm = alloc->mm;
+	struct vm_area_struct *vma;
+	int ret = -ESRCH;
+
+	/* attempt per-vma lock first */
+	vma = lock_vma_under_rcu(mm, addr);
+	if (vma) {
+		if (binder_alloc_is_mapped(alloc))
+			ret = vm_insert_page(vma, addr, page);
+		vma_end_read(vma);
+		return ret;
+	}
+
+	/* fall back to mmap_lock */
+	mmap_read_lock(mm);
+	vma = vma_lookup(mm, addr);
+	if (vma && binder_alloc_is_mapped(alloc))
+		ret = vm_insert_page(vma, addr, page);
+	mmap_read_unlock(mm);
+
+	return ret;
+}
+
 static struct page *binder_page_alloc(struct binder_alloc *alloc,
 				      unsigned long index)
 {
@@ -268,9 +315,7 @@ static int binder_install_single_page(struct binder_alloc *alloc,
 				      unsigned long index,
 				      unsigned long addr)
 {
-	struct vm_area_struct *vma;
 	struct page *page;
-	long npages;
 	int ret;
 
 	if (!mmget_not_zero(alloc->mm))
@@ -282,16 +327,7 @@ static int binder_install_single_page(struct binder_alloc *alloc,
 		goto out;
 	}
 
-	mmap_read_lock(alloc->mm);
-	vma = vma_lookup(alloc->mm, addr);
-	if (!vma || !binder_alloc_is_mapped(alloc)) {
-		binder_free_page(page);
-		pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
-		ret = -ESRCH;
-		goto unlock;
-	}
-
-	ret = vm_insert_page(vma, addr, page);
+	ret = binder_page_insert(alloc, addr, page);
 	switch (ret) {
 	case -EBUSY:
 		/*
@@ -301,9 +337,8 @@ static int binder_install_single_page(struct binder_alloc *alloc,
 		 */
 		ret = 0;
 		binder_free_page(page);
-		npages = get_user_pages_remote(alloc->mm, addr, 1,
-					       FOLL_NOFAULT, &page, NULL);
-		if (npages <= 0) {
+		page = binder_page_lookup(alloc, addr);
+		if (!page) {
 			pr_err("%d: failed to find page at offset %lx\n",
 			       alloc->pid, addr - alloc->vm_start);
 			ret = -ESRCH;
@@ -321,8 +356,6 @@ static int binder_install_single_page(struct binder_alloc *alloc,
 		ret = -ENOMEM;
 		break;
 	}
-unlock:
-	mmap_read_unlock(alloc->mm);
 out:
 	mmput_async(alloc->mm);
 	return ret;
-- 
2.47.0.338.g60cca15819-goog