media: videobuf2: revert "get_userptr: buffers are always writable"

Commit 707947247e ("media: videobuf2-vmalloc: get_userptr: buffers are
always writable") caused problems in a corner case (passing read-only
shmem memory as a userptr). So revert this patch.

The original problem for which that commit was originally made is
something that I could not reproduce after reverting it. So just go
back to the way it was for many years, and if problems arise in
the future, then another approach should be taken to resolve it.

This patch is based on a patch from Hirokazu.

Fixes: 707947247e ("media: videobuf2-vmalloc: get_userptr: buffers are always writable")
Signed-off-by: Hirokazu Honda <hiroh@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/common/videobuf2/frame_vector.c

@@ -14,6 +14,7 @@
  * get_vaddr_frames() - map virtual addresses to pfns
  * @start:	starting user address
  * @nr_frames:	number of pages / pfns from start to map
+ * @write:	the mapped address has write permission
  * @vec:	structure which receives pages / pfns of the addresses mapped.
  *		It should have space for at least nr_frames entries.
  *
@@ -32,7 +33,7 @@
  *
  * This function takes care of grabbing mmap_lock as necessary.
  */
-int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
+int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
 		     struct frame_vector *vec)
 {
 	struct mm_struct *mm = current->mm;
@@ -40,6 +41,7 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 	int ret_pin_user_pages_fast = 0;
 	int ret = 0;
 	int err;
+	unsigned int gup_flags = FOLL_FORCE | FOLL_LONGTERM;
 
 	if (nr_frames == 0)
 		return 0;
@@ -49,8 +51,10 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 
 	start = untagged_addr(start);
 
-	ret = pin_user_pages_fast(start, nr_frames,
-				  FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
+	if (write)
+		gup_flags |= FOLL_WRITE;
+
+	ret = pin_user_pages_fast(start, nr_frames, gup_flags,
 				  (struct page **)(vec->ptrs));
 	if (ret > 0) {
 		vec->got_ref = true;

drivers/media/common/videobuf2/videobuf2-dma-contig.c

@@ -603,7 +603,8 @@ static void *vb2_dc_get_userptr(struct vb2_buffer *vb, struct device *dev,
 	buf->vb = vb;
 
 	offset = lower_32_bits(offset_in_page(vaddr));
-	vec = vb2_create_framevec(vaddr, size);
+	vec = vb2_create_framevec(vaddr, size, buf->dma_dir == DMA_FROM_DEVICE ||
+					       buf->dma_dir == DMA_BIDIRECTIONAL);
 	if (IS_ERR(vec)) {
 		ret = PTR_ERR(vec);
 		goto fail_buf;

drivers/media/common/videobuf2/videobuf2-dma-sg.c

@@ -241,7 +241,9 @@ static void *vb2_dma_sg_get_userptr(struct vb2_buffer *vb, struct device *dev,
 	buf->size = size;
 	buf->dma_sgt = &buf->sg_table;
 	buf->vb = vb;
-	vec = vb2_create_framevec(vaddr, size);
+	vec = vb2_create_framevec(vaddr, size,
+				  buf->dma_dir == DMA_FROM_DEVICE ||
+				  buf->dma_dir == DMA_BIDIRECTIONAL);
 	if (IS_ERR(vec))
 		goto userptr_fail_pfnvec;
 	buf->vec = vec;

drivers/media/common/videobuf2/videobuf2-memops.c

@@ -26,6 +26,7 @@
  * vb2_create_framevec() - map virtual addresses to pfns
  * @start:	Virtual user address where we start mapping
  * @length:	Length of a range to map
+ * @write:	Should we map for writing into the area
  *
  * This function allocates and fills in a vector with pfns corresponding to
  * virtual address range passed in arguments. If pfns have corresponding pages,
@@ -34,7 +35,8 @@
  * failure. Returned vector needs to be freed via vb2_destroy_pfnvec().
  */
 struct frame_vector *vb2_create_framevec(unsigned long start,
-					 unsigned long length)
+					 unsigned long length,
+					 bool write)
 {
 	int ret;
 	unsigned long first, last;
@@ -47,7 +49,7 @@ struct frame_vector *vb2_create_framevec(unsigned long start,
 	vec = frame_vector_create(nr);
 	if (!vec)
 		return ERR_PTR(-ENOMEM);
-	ret = get_vaddr_frames(start & PAGE_MASK, nr, vec);
+	ret = get_vaddr_frames(start & PAGE_MASK, nr, write, vec);
 	if (ret < 0)
 		goto out_destroy;
 	/* We accept only complete set of PFNs */

drivers/media/common/videobuf2/videobuf2-vmalloc.c

@@ -85,7 +85,9 @@ static void *vb2_vmalloc_get_userptr(struct vb2_buffer *vb, struct device *dev,
 	buf->dma_dir = vb->vb2_queue->dma_dir;
 	offset = vaddr & ~PAGE_MASK;
 	buf->size = size;
-	vec = vb2_create_framevec(vaddr, size);
+	vec = vb2_create_framevec(vaddr, size,
+				  buf->dma_dir == DMA_FROM_DEVICE ||
+				  buf->dma_dir == DMA_BIDIRECTIONAL);
 	if (IS_ERR(vec)) {
 		ret = PTR_ERR(vec);
 		goto fail_pfnvec_create;

include/media/frame_vector.h

@@ -16,7 +16,7 @@ struct frame_vector {
 struct frame_vector *frame_vector_create(unsigned int nr_frames);
 void frame_vector_destroy(struct frame_vector *vec);
 int get_vaddr_frames(unsigned long start, unsigned int nr_pfns,
-		     struct frame_vector *vec);
+		     bool write, struct frame_vector *vec);
 void put_vaddr_frames(struct frame_vector *vec);
 int frame_vector_to_pages(struct frame_vector *vec);
 void frame_vector_to_pfns(struct frame_vector *vec);

include/media/videobuf2-memops.h

@@ -34,7 +34,8 @@ struct vb2_vmarea_handler {
 extern const struct vm_operations_struct vb2_common_vm_ops;
 
 struct frame_vector *vb2_create_framevec(unsigned long start,
-					 unsigned long length);
+					 unsigned long length,
+					 bool write);
 void vb2_destroy_framevec(struct frame_vector *vec);
 
 #endif