The arguments are the same as munmap() except that the start of the
mapping is specified as an offset into the mshare region instead of
as an address.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 include/uapi/linux/msharefs.h |  7 ++++++
 mm/mshare.c                   | 40 +++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/include/uapi/linux/msharefs.h b/include/uapi/linux/msharefs.h
index ad129beeef62..fb0235d1e384 100644
--- a/include/uapi/linux/msharefs.h
+++ b/include/uapi/linux/msharefs.h
@@ -19,6 +19,7 @@
  * msharefs specific ioctl commands
  */
 #define MSHAREFS_CREATE_MAPPING	_IOW('x', 0,  struct mshare_create)
+#define MSHAREFS_UNMAP		_IOW('x', 1,  struct mshare_unmap)
 
 struct mshare_create {
 	__u64 region_offset;
@@ -28,4 +29,10 @@ struct mshare_create {
 	__u32 flags;
 	__u32 fd;
 };
+
+struct mshare_unmap {
+	__u64 region_offset;
+	__u64 size;
+};
+
 #endif
diff --git a/mm/mshare.c b/mm/mshare.c
index be0aaa894963..a6106f6264cb 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -281,11 +281,41 @@ msharefs_create_mapping(struct mshare_data *m_data, struct mshare_create *mcreat
 	return error;
 }
 
+static long
+msharefs_unmap(struct mshare_data *m_data, struct mshare_unmap *munmap)
+{
+	struct mm_struct *host_mm = m_data->mm;
+	unsigned long mshare_start, mshare_end, mshare_size;
+	unsigned long region_offset = munmap->region_offset;
+	unsigned long size = munmap->size;
+	unsigned long addr;
+	int error;
+
+	mshare_start = m_data->start;
+	mshare_size = m_data->size;
+	mshare_end = mshare_start + mshare_size;
+	addr = mshare_start + region_offset;
+
+	if ((size > mshare_size) || (region_offset >= mshare_size) ||
+	    (addr + size > mshare_end))
+		return -EINVAL;
+
+	if (mmap_write_lock_killable(host_mm))
+		return -EINTR;
+
+	error = do_munmap(host_mm, addr, size, NULL);
+
+	mmap_write_unlock(host_mm);
+
+	return error;
+}
+
 static long
 msharefs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct mshare_data *m_data = filp->private_data;
 	struct mshare_create mcreate;
+	struct mshare_unmap munmap;
 
 	switch (cmd) {
 	case MSHAREFS_CREATE_MAPPING:
@@ -298,6 +328,16 @@ msharefs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 		return msharefs_create_mapping(m_data, &mcreate);
 
+	case MSHAREFS_UNMAP:
+		if (copy_from_user(&munmap, (struct mshare_unmap __user *)arg,
+			sizeof(munmap)))
+			return -EFAULT;
+
+		if (!test_bit(MSHARE_INITIALIZED, &m_data->flags))
+			return -EINVAL;
+
+		return msharefs_unmap(m_data, &munmap);
+
 	default:
 		return -ENOTTY;
 	}
-- 
2.43.5