ANDROID: dmabuf: Add mmap_count to struct dmabuf

mmap_count can be used to  efficiently calculate the
PSS for any DMA buffer that the process has mapped.

Bug: 167141117
Change-Id: I8296981f0135a5532969aca3a8baa5da61dfe39f
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers

@@ -50,3 +50,10 @@ KernelVersion:	v5.12
 Contact:	Hridya Valsaraju <hridya@google.com>
 Description:	This file is read-only and contains a map_counter indicating the
 		number of distinct device mappings of the attachment.
+
+What:		/sys/kernel/dmabuf/buffers/<inode_number>/mmap_count
+Date:		January 2021
+KernelVersion:	v5.10
+Contact:	Kalesh Singh <kaleshsingh@google.com>
+Description:	This file is read-only and contains a counter indicating the
+		number of times the buffer has been mmap().

drivers/dma-buf/dma-buf-sysfs-stats.c

@@ -52,6 +52,13 @@ static ssize_t exporter_name_show(struct dma_buf *dmabuf,
 	return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
 }
 
+static ssize_t mmap_count_show(struct dma_buf *dmabuf,
+		struct dma_buf_stats_attribute *attr,
+		char *buf)
+{
+	return sysfs_emit(buf, "%d\n", dmabuf->mmap_count);
+}
+
 static ssize_t size_show(struct dma_buf *dmabuf,
 			 struct dma_buf_stats_attribute *attr,
 			 char *buf)
@@ -62,10 +69,13 @@ static ssize_t size_show(struct dma_buf *dmabuf,
 static struct dma_buf_stats_attribute exporter_name_attribute =
 	__ATTR_RO(exporter_name);
 static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
+static struct dma_buf_stats_attribute mmap_count_attribute =
+	__ATTR_RO(mmap_count);
 
 static struct attribute *dma_buf_stats_default_attrs[] = {
 	&exporter_name_attribute.attr,
 	&size_attribute.attr,
+	&mmap_count_attribute.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(dma_buf_stats_default);

drivers/dma-buf/dma-buf.c

@@ -127,6 +127,54 @@ static struct file_system_type dma_buf_fs_type = {
 	.kill_sb = kill_anon_super,
 };
 
+#ifdef CONFIG_DMABUF_SYSFS_STATS
+static void dma_buf_vma_open(struct vm_area_struct *vma)
+{
+	struct dma_buf *dmabuf = vma->vm_file->private_data;
+
+	dmabuf->mmap_count++;
+	/* call the heap provided vma open() op */
+	if (dmabuf->exp_vm_ops->open)
+		dmabuf->exp_vm_ops->open(vma);
+}
+
+static void dma_buf_vma_close(struct vm_area_struct *vma)
+{
+	struct dma_buf *dmabuf = vma->vm_file->private_data;
+
+	if (dmabuf->mmap_count)
+		dmabuf->mmap_count--;
+	/* call the heap provided vma close() op */
+	if (dmabuf->exp_vm_ops->close)
+		dmabuf->exp_vm_ops->close(vma);
+}
+
+static int dma_buf_do_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+	/* call this first because the exporter might override vma->vm_ops */
+	int ret = dmabuf->ops->mmap(dmabuf, vma);
+
+	if (ret)
+		return ret;
+
+	/* save the exporter provided vm_ops */
+	dmabuf->exp_vm_ops = vma->vm_ops;
+	dmabuf->vm_ops = *(dmabuf->exp_vm_ops);
+	/* override open() and close() to provide buffer mmap count */
+	dmabuf->vm_ops.open = dma_buf_vma_open;
+	dmabuf->vm_ops.close = dma_buf_vma_close;
+	vma->vm_ops = &dmabuf->vm_ops;
+	dmabuf->mmap_count++;
+
+	return ret;
+}
+#else	/* CONFIG_DMABUF_SYSFS_STATS */
+static int dma_buf_do_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+	return dmabuf->ops->mmap(dmabuf, vma);
+}
+#endif	/* CONFIG_DMABUF_SYSFS_STATS */
+
 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;
@@ -145,7 +193,7 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;
 
-	return dmabuf->ops->mmap(dmabuf, vma);
+	return dma_buf_do_mmap(dmabuf, vma);
 }
 
 static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)

include/linux/dma-buf.h

@@ -381,6 +381,9 @@ struct dma_buf_ops {
  * @sysfs_entry: for exposing information about this buffer in sysfs.
  * The attachment_uid member of @sysfs_entry is protected by dma_resv lock
  * and is incremented on each attach.
+ * @mmap_count: number of times buffer has been mmapped.
+ * @exp_vm_ops: the vm ops provided by the buffer exporter.
+ * @vm_ops: the overridden vm_ops used to track mmap_count of the buffer.
  *
  * This represents a shared buffer, created by calling dma_buf_export(). The
  * userspace representation is a normal file descriptor, which can be created by
@@ -424,6 +427,9 @@ struct dma_buf {
 		unsigned int attachment_uid;
 		struct kset *attach_stats_kset;
 	} *sysfs_entry;
+	int mmap_count;
+	const struct vm_operations_struct *exp_vm_ops;
+	struct vm_operations_struct vm_ops;
 #endif
 };