[PATCH] dma-buf: Deny copy-on-writes mmaps

[Andi Shyti <andi.shyti@linux.intel.com>]

From: Chris Wilson <chris.p.wilson@linux.intel.com>

Enforce that an mmap of a dmabuf is always using MAP_SHARED so that all
access (both read and writes) using the device memory and not a local
copy-on-write page in system memory.

Signed-off-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
---
 drivers/dma-buf/dma-buf.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 21916bba77d5..1ec297241842 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -25,6 +25,7 @@
 #include <linux/poll.h>
 #include <linux/dma-resv.h>
 #include <linux/mm.h>
+#include <linux/mman.h>
 #include <linux/mount.h>
 #include <linux/pseudo_fs.h>
 
@@ -128,6 +129,19 @@ static struct file_system_type dma_buf_fs_type = {
 	.kill_sb = kill_anon_super,
 };
 
+static unsigned long
+dma_buf_get_unmapped_area(struct file *file,
+			  unsigned long addr,
+			  unsigned long len,
+			  unsigned long pgoff,
+			  unsigned long flags)
+{
+	if ((flags & MAP_TYPE) == MAP_PRIVATE)
+		return -EINVAL;
+
+	return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
+}
+
 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;
@@ -508,6 +522,7 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
 
 static const struct file_operations dma_buf_fops = {
 	.release	= dma_buf_file_release,
+	.get_unmapped_area = dma_buf_get_unmapped_area,
 	.mmap		= dma_buf_mmap_internal,
 	.llseek		= dma_buf_llseek,
 	.poll		= dma_buf_poll,
-- 
2.40.1