drm/vmwgfx: Avoid pinning fbdev framebuffers

fbdev framebuffers were previously pinned to be able to keep them mapped
across updates.

This commit introduces a mechanism that instead revalidates the map on
each update, keeping the map cached across updates. The cached map is torn
down if the underlying pages change. Typically on buffer object moves and
swapouts.

This should be nicer to the system when we have resource contention.

Testing done: Basic fbdev functionality under Fedora 27.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Deepak Rawat <drawat@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -354,6 +354,7 @@ void vmw_dmabuf_bo_free(struct ttm_buffer_object *bo)
 {
 	struct vmw_dma_buffer *vmw_bo = vmw_dma_buffer(bo);
 
+	vmw_dma_buffer_unmap(vmw_bo);
 	kfree(vmw_bo);
 }
 
@@ -361,6 +362,7 @@ static void vmw_user_dmabuf_destroy(struct ttm_buffer_object *bo)
 {
 	struct vmw_user_dma_buffer *vmw_user_bo = vmw_user_dma_buffer(bo);
 
+	vmw_dma_buffer_unmap(&vmw_user_bo->dma);
 	ttm_prime_object_kfree(vmw_user_bo, prime);
 }
 
@@ -1239,6 +1241,12 @@ void vmw_resource_move_notify(struct ttm_buffer_object *bo,
 
 	dma_buf = container_of(bo, struct vmw_dma_buffer, base);
 
+	/*
+	 * Kill any cached kernel maps before move. An optimization could
+	 * be to do this iff source or destination memory type is VRAM.
+	 */
+	vmw_dma_buffer_unmap(dma_buf);
+
 	if (mem->mem_type != VMW_PL_MOB) {
 		struct vmw_resource *res, *n;
 		struct ttm_validate_buffer val_buf;
@@ -1262,6 +1270,21 @@ void vmw_resource_move_notify(struct ttm_buffer_object *bo,
 }
 
 
+/**
+ * vmw_resource_swap_notify - swapout notify callback.
+ *
+ * @bo: The buffer object to be swapped out.
+ */
+void vmw_resource_swap_notify(struct ttm_buffer_object *bo)
+{
+	if (bo->destroy != vmw_dmabuf_bo_free &&
+	    bo->destroy != vmw_user_dmabuf_destroy)
+		return;
+
+	/* Kill any cached kernel maps before swapout */
+	vmw_dma_buffer_unmap(vmw_dma_buffer(bo));
+}
+
 
 /**
  * vmw_query_readback_all - Read back cached query states