[PATCH 07/20] 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. Disallow operations that
could split the resulting msharefs vma such as partial unmaps and
protection changes. Fault handling, mapping, unmapping, and
protection changes for objects mapped into an mshare region will
be done using the shared vmas created for them in the host mm. This
functionality will be added in later patches.

Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 mm/mshare.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/mm/mshare.c b/mm/mshare.c
index 056cb5a82547..529a90fe1602 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -16,6 +16,7 @@
 
 #include <linux/fs.h>
 #include <linux/fs_context.h>
+#include <linux/mman.h>
 #include <linux/spinlock_types.h>
 #include <uapi/linux/magic.h>
 #include <uapi/linux/msharefs.h>
@@ -28,6 +29,74 @@ struct mshare_data {
 	struct mshare_info minfo;
 };
 
+static int mshare_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
+{
+	return -EINVAL;
+}
+
+static int mshare_vm_op_mprotect(struct vm_area_struct *vma, unsigned long start,
+				 unsigned long end, unsigned long newflags)
+{
+	return -EINVAL;
+}
+
+static const struct vm_operations_struct msharefs_vm_ops = {
+	.may_split = mshare_vm_op_split,
+	.mprotect = mshare_vm_op_mprotect,
+};
+
+/*
+ * 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;
+
+	vma->vm_private_data = m_data;
+	vm_flags_set(vma, VM_MSHARE | VM_DONTEXPAND);
+	vma->vm_ops = &msharefs_vm_ops;
+
+	return 0;
+}
+
+static unsigned long
+msharefs_get_unmapped_area(struct file *file, unsigned long addr,
+		unsigned long len, unsigned long pgoff, unsigned long flags)
+{
+	struct mshare_data *m_data = file->private_data;
+	struct mm_struct *mm = current->mm;
+	unsigned long mshare_start, mshare_size;
+	const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
+
+	mmap_assert_write_locked(mm);
+
+	if ((flags & MAP_TYPE) == MAP_PRIVATE)
+		return -EINVAL;
+
+	spin_lock(&m_data->m_lock);
+	mshare_start = m_data->minfo.start;
+	mshare_size = m_data->minfo.size;
+	spin_unlock(&m_data->m_lock);
+
+	if ((mshare_size == 0) || (len != mshare_size))
+		return -EINVAL;
+
+	if (len > mmap_end - mmap_min_addr)
+		return -ENOMEM;
+
+	if (addr && (addr != mshare_start))
+		return -EINVAL;
+
+	if (flags & MAP_FIXED)
+		return addr;
+
+	if (find_vma_intersection(mm, mshare_start, mshare_start + mshare_size))
+		return -EEXIST;
+
+	return mshare_start;
+}
+
 static long
 msharefs_set_size(struct mm_struct *host_mm, struct mshare_data *m_data,
 			struct mshare_info *minfo)
@@ -94,6 +163,8 @@ static const struct inode_operations msharefs_file_inode_ops;
 
 static const struct file_operations msharefs_file_operations = {
 	.open		= simple_open,
+	.mmap		= msharefs_mmap,
+	.get_unmapped_area	 = msharefs_get_unmapped_area,
 	.unlocked_ioctl	= msharefs_ioctl,
 };
 
-- 
2.43.5