drm: add flag for mapping PCI DMA buffers read-only.

Add DRM_PCI_BUFFER_RO flag for mapping PCI DMA buffer read-only. An additional
flag is needed, since PCI DMA buffers do not have an associated map.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm.h

@@ -356,7 +356,8 @@ typedef struct drm_buf_desc {
 		_DRM_PAGE_ALIGN = 0x01,	/**< Align on page boundaries for DMA */
 		_DRM_AGP_BUFFER = 0x02,	/**< Buffer is in AGP space */
 		_DRM_SG_BUFFER = 0x04,	/**< Scatter/gather memory buffer */
-		_DRM_FB_BUFFER = 0x08	/**< Buffer is in frame buffer */
+		_DRM_FB_BUFFER = 0x08,	/**< Buffer is in frame buffer */
+		_DRM_PCI_BUFFER_RO = 0x10 /**< Map PCI DMA buffer read-only */
 	} flags;
 	unsigned long agp_start; /**<
 				  * Start address of where the AGP buffers are

drivers/char/drm/drmP.h

@@ -431,7 +431,8 @@ typedef struct drm_device_dma {
 	enum {
 		_DRM_DMA_USE_AGP = 0x01,
 		_DRM_DMA_USE_SG = 0x02,
-		_DRM_DMA_USE_FB = 0x04
+		_DRM_DMA_USE_FB = 0x04,
+		_DRM_DMA_USE_PCI_RO = 0x08
 	} flags;
 
 } drm_device_dma_t;

drivers/char/drm/drm_bufs.c

@@ -887,6 +887,9 @@ int drm_addbufs_pci(drm_device_t * dev, drm_buf_desc_t * request)
 	request->count = entry->buf_count;
 	request->size = size;
 
+	if (request->flags & _DRM_PCI_BUFFER_RO)
+		dma->flags = _DRM_DMA_USE_PCI_RO;
+
 	atomic_dec(&dev->buf_alloc);
 	return 0;
 
@@ -1471,9 +1474,10 @@ int drm_freebufs(struct inode *inode, struct file *filp,
  * \param arg pointer to a drm_buf_map structure.
  * \return zero on success or a negative number on failure.
  *
- * Maps the AGP or SG buffer region with do_mmap(), and copies information
- * about each buffer into user space. The PCI buffers are already mapped on the
- * addbufs_pci() call.
+ * Maps the AGP, SG or PCI buffer region with do_mmap(), and copies information
+ * about each buffer into user space. For PCI buffers, it calls do_mmap() with
+ * offset equal to 0, which drm_mmap() interpretes as PCI buffers and calls
+ * drm_mmap_dma().
  */
 int drm_mapbufs(struct inode *inode, struct file *filp,
 		unsigned int cmd, unsigned long arg)

drivers/char/drm/drm_vm.c

@@ -473,6 +473,22 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma)
 	}
 	unlock_kernel();
 
+	if (!capable(CAP_SYS_ADMIN) &&
+	    (dma->flags & _DRM_DMA_USE_PCI_RO)) {
+		vma->vm_flags &= ~(VM_WRITE | VM_MAYWRITE);
+#if defined(__i386__) || defined(__x86_64__)
+		pgprot_val(vma->vm_page_prot) &= ~_PAGE_RW;
+#else
+		/* Ye gads this is ugly.  With more thought
+		   we could move this up higher and use
+		   `protection_map' instead.  */
+		vma->vm_page_prot =
+		    __pgprot(pte_val
+			     (pte_wrprotect
+			      (__pte(pgprot_val(vma->vm_page_prot)))));
+#endif
+	}
+
 	vma->vm_ops = &drm_vm_dma_ops;
 
 	vma->vm_flags |= VM_RESERVED;	/* Don't swap */