staging: vboxvideo: Fix modeset / page_flip error handling

The default settings for Linux vms created in VirtualBox allocate only
16M of videomem. When running fullscreen on a 1920x1080 (or bigger) monitor
this is not a lot.

When using GNOME3 on Wayland we have already been seeing out of video
memory errors for a while now. After commit 2408898e ("staging:
vboxvideo: Add page-flip support") this has become much worse as now
multiple buffers are used.

There is nothing we can do about there not being enough video-mem, but
we should handle running out of video-mem properly, currently there are
2 problems with this:

1) vbox_crtc_mode_set() does not check if vbox_crtc_mode_set_base() fails
at all and does not properly propagate the oom error.

2) vbox_crtc_do_set_base() unpins the old fb too soon:

2.1) It unpins it before pinning the new fb, so if the pinning of the new
fb fails (which it will when we run out of video-mem), then we also cannot
fall back to the old-fb as it has been already unpinned. We could try to
re-pin it but there is no guarantee that will succeed.

2.2) It unpins it before reprogramming the hardware to scan out from the
new-fb, which could lead to some ugliness where the hw is scanning out the
oldfb while it is being replaced with something else.

Fixing this requires to do things in this order:
1) Pin the new fb
2) Program the hw
3) Unpin the oldfb

This needs to be done for both a mode_set and for a page_flip so this
commit re-writes vbox_crtc_do_set_base() into vbox_crtc_set_base_and_mode()
which does this in the correct order, putting the hardware programming
which was duplicated between the mode_set and page_flip code inside the
new function.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vboxvideo/vbox_mode.c

@@ -221,53 +221,68 @@ static bool vbox_set_up_input_mapping(struct vbox_private *vbox)
 	return old_single_framebuffer != vbox->single_framebuffer;
 }
 
-static int vbox_crtc_do_set_base(struct drm_crtc *crtc,
-				 struct drm_framebuffer *old_fb,
-				 struct drm_framebuffer *new_fb,
-				 int x, int y)
+static int vbox_fb_pin(struct drm_framebuffer *fb, u64 *addr)
+{
+	struct vbox_bo *bo = gem_to_vbox_bo(to_vbox_framebuffer(fb)->obj);
+	int ret;
+
+	ret = vbox_bo_reserve(bo, false);
+	if (ret)
+		return ret;
+
+	ret = vbox_bo_pin(bo, TTM_PL_FLAG_VRAM, addr);
+	vbox_bo_unreserve(bo);
+	return ret;
+}
+
+static void vbox_fb_unpin(struct drm_framebuffer *fb)
 {
-	struct vbox_private *vbox = crtc->dev->dev_private;
-	struct vbox_crtc *vbox_crtc = to_vbox_crtc(crtc);
-	struct drm_gem_object *obj;
-	struct vbox_framebuffer *vbox_fb;
 	struct vbox_bo *bo;
 	int ret;
-	u64 gpu_addr;
 
-	/* Unpin the previous fb. */
-	if (old_fb) {
-		vbox_fb = to_vbox_framebuffer(old_fb);
-		obj = vbox_fb->obj;
-		bo = gem_to_vbox_bo(obj);
-		ret = vbox_bo_reserve(bo, false);
-		if (ret)
-			return ret;
+	if (!fb)
+		return;
 
-		vbox_bo_unpin(bo);
-		vbox_bo_unreserve(bo);
+	bo = gem_to_vbox_bo(to_vbox_framebuffer(fb)->obj);
+
+	ret = vbox_bo_reserve(bo, false);
+	if (ret) {
+		DRM_ERROR("Error %d reserving fb bo, leaving it pinned\n", ret);
+		return;
 	}
 
-	vbox_fb = to_vbox_framebuffer(new_fb);
-	obj = vbox_fb->obj;
-	bo = gem_to_vbox_bo(obj);
+	vbox_bo_unpin(bo);
+	vbox_bo_unreserve(bo);
+}
 
-	ret = vbox_bo_reserve(bo, false);
-	if (ret)
-		return ret;
+static int vbox_crtc_set_base_and_mode(struct drm_crtc *crtc,
+				       struct drm_framebuffer *old_fb,
+				       struct drm_framebuffer *new_fb,
+				       struct drm_display_mode *mode,
+				       int x, int y)
+{
+	struct vbox_private *vbox = crtc->dev->dev_private;
+	struct vbox_crtc *vbox_crtc = to_vbox_crtc(crtc);
+	u64 gpu_addr;
+	int ret;
 
-	ret = vbox_bo_pin(bo, TTM_PL_FLAG_VRAM, &gpu_addr);
+	/* Prepare: pin the new framebuffer bo */
+	ret = vbox_fb_pin(new_fb, &gpu_addr);
 	if (ret) {
-		vbox_bo_unreserve(bo);
+		DRM_WARN("Error %d pinning new fb, out of video mem?\n", ret);
 		return ret;
 	}
 
-	if (&vbox->fbdev->afb == vbox_fb)
+	/* Commit: Update hardware to use the new fb */
+	mutex_lock(&vbox->hw_mutex);
+
+	if (&vbox->fbdev->afb == to_vbox_framebuffer(new_fb))
 		vbox_fbdev_set_base(vbox, gpu_addr);
-	vbox_bo_unreserve(bo);
 
-	/* vbox_set_start_address_crt1(crtc, (u32)gpu_addr); */
 	vbox_crtc->fb_offset = gpu_addr;
-	if (vbox_set_up_input_mapping(vbox)) {
+
+	/* vbox_do_modeset() checks vbox->single_framebuffer so update it now */
+	if (mode && vbox_set_up_input_mapping(vbox)) {
 		struct drm_crtc *crtci;
 
 		list_for_each_entry(crtci, &vbox->dev->mode_config.crtc_list,
@@ -277,13 +292,20 @@ static int vbox_crtc_do_set_base(struct drm_crtc *crtc,
 		}
 	}
 
-	return 0;
-}
+	vbox_set_view(crtc);
+	vbox_do_modeset(crtc, mode ? mode : &crtc->mode);
 
-static int vbox_crtc_mode_set_base(struct drm_crtc *crtc, int x, int y,
-				   struct drm_framebuffer *old_fb)
-{
-	return vbox_crtc_do_set_base(crtc, old_fb, CRTC_FB(crtc), x, y);
+	if (mode)
+		hgsmi_update_input_mapping(vbox->guest_pool, 0, 0,
+					   vbox->input_mapping_width,
+					   vbox->input_mapping_height);
+
+	mutex_unlock(&vbox->hw_mutex);
+
+	/* Cleanup: unpin the old fb */
+	vbox_fb_unpin(old_fb);
+
+	return 0;
 }
 
 static int vbox_crtc_mode_set(struct drm_crtc *crtc,
@@ -291,21 +313,8 @@ static int vbox_crtc_mode_set(struct drm_crtc *crtc,
 			      struct drm_display_mode *adjusted_mode,
 			      int x, int y, struct drm_framebuffer *old_fb)
 {
-	struct vbox_private *vbox = crtc->dev->dev_private;
-	int ret;
-
-	vbox_crtc_mode_set_base(crtc, x, y, old_fb);
-
-	mutex_lock(&vbox->hw_mutex);
-	ret = vbox_set_view(crtc);
-	if (!ret)
-		vbox_do_modeset(crtc, mode);
-	hgsmi_update_input_mapping(vbox->guest_pool, 0, 0,
-				   vbox->input_mapping_width,
-				   vbox->input_mapping_height);
-	mutex_unlock(&vbox->hw_mutex);
-
-	return ret;
+	return vbox_crtc_set_base_and_mode(crtc, old_fb, CRTC_FB(crtc),
+					   mode, x, y);
 }
 
 static int vbox_crtc_page_flip(struct drm_crtc *crtc,
@@ -319,15 +328,10 @@ static int vbox_crtc_page_flip(struct drm_crtc *crtc,
 	unsigned long flags;
 	int rc;
 
-	rc = vbox_crtc_do_set_base(crtc, CRTC_FB(crtc), fb, 0, 0);
+	rc = vbox_crtc_set_base_and_mode(crtc, CRTC_FB(crtc), fb, NULL, 0, 0);
 	if (rc)
 		return rc;
 
-	mutex_lock(&vbox->hw_mutex);
-	vbox_set_view(crtc);
-	vbox_do_modeset(crtc, &crtc->mode);
-	mutex_unlock(&vbox->hw_mutex);
-
 	spin_lock_irqsave(&drm->event_lock, flags);
 
 	if (event)
@@ -354,7 +358,6 @@ static const struct drm_crtc_helper_funcs vbox_crtc_helper_funcs = {
 	.dpms = vbox_crtc_dpms,
 	.mode_fixup = vbox_crtc_mode_fixup,
 	.mode_set = vbox_crtc_mode_set,
-	/* .mode_set_base = vbox_crtc_mode_set_base, */
 	.disable = vbox_crtc_disable,
 	.prepare = vbox_crtc_prepare,
 	.commit = vbox_crtc_commit,