[RFC PATCH v3 07/10] mm/mshare: Add mmap support

[Anthony Yznaga <anthony.yznaga@oracle.com>]

From: Khalid Aziz <khalid@kernel.org>

Add support for mapping an mshare region into a process after the
region has been established in msharefs. For now, disallow partial
unmaps of the region by disallowing splitting of an mshare VMA.
The functionality for mapping an object into an mshare region
will added in later patches.

Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 mm/mshare.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/mm/mshare.c b/mm/mshare.c
index af46eb76d2bc..f3f6ed9c3761 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -33,6 +33,63 @@ struct msharefs_info {
 static const struct inode_operations msharefs_dir_inode_ops;
 static const struct inode_operations msharefs_file_inode_ops;
 
+/*
+ * Disallow partial unmaps of an mshare region for now. Unmapping at
+ * boundaries aligned to the level page tables are shared at could
+ * be allowed in the future.
+ */ 
+static int mshare_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
+{
+	return -EINVAL;
+}
+
+static const struct vm_operations_struct msharefs_vm_ops = {
+	.may_split = mshare_vm_op_split,
+};
+
+/*
+ * msharefs_mmap() - mmap an mshare region
+ */
+static int
+msharefs_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct mshare_data *m_data = file->private_data;
+	unsigned long mshare_start, mshare_end;
+	int err = -EINVAL;
+
+	spin_lock(&m_data->m_lock);
+	mshare_start = m_data->minfo.start;
+	mshare_end = mshare_start + m_data->minfo.size;
+	spin_unlock(&m_data->m_lock);
+
+	/*
+	 * Make sure start and end of this mshare region has
+	 * been established already
+	 */
+	if (mshare_start == 0)
+		goto err_out;
+
+	/*
+	 * Verify alignment and size multiple
+	 */
+	if ((vma->vm_start | vma->vm_end) & (PGDIR_SIZE - 1))
+		goto err_out;
+
+	/*
+	 * Verify this mapping does not extend outside of mshare region
+	 */
+	if (vma->vm_start < mshare_start || vma->vm_end > mshare_end)
+		goto err_out;
+
+	err = 0;
+	vma->vm_private_data = m_data;
+	vm_flags_set(vma, VM_SHARED_PT);
+	vma->vm_ops = &msharefs_vm_ops;
+
+err_out:
+	return err;
+}
+
 static long
 msharefs_set_size(struct mm_struct *mm, struct mshare_data *m_data,
 			struct mshare_info *minfo)
@@ -100,6 +157,7 @@ msharefs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 static const struct file_operations msharefs_file_operations = {
 	.open		= simple_open,
+	.mmap		= msharefs_mmap,
 	.unlocked_ioctl	= msharefs_ioctl,
 	.llseek		= no_llseek,
 };
-- 
2.43.5