diff --git a/drivers/gpu/drm/i915/gvt/handlers.c b/drivers/gpu/drm/i915/gvt/handlers.c
index a6ade66349bd..25f78196b964 100644
--- a/drivers/gpu/drm/i915/gvt/handlers.c
+++ b/drivers/gpu/drm/i915/gvt/handlers.c
@@ -1254,18 +1254,15 @@ static int send_display_ready_uevent(struct intel_vgpu *vgpu, int ready)
 static int pvinfo_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,
 		void *p_data, unsigned int bytes)
 {
-	u32 data;
-	int ret;
-
-	write_vreg(vgpu, offset, p_data, bytes);
-	data = vgpu_vreg(vgpu, offset);
+	u32 data = *(u32 *)p_data;
+	bool invalid_write = false;
 
 	switch (offset) {
 	case _vgtif_reg(display_ready):
 		send_display_ready_uevent(vgpu, data ? 1 : 0);
 		break;
 	case _vgtif_reg(g2v_notify):
-		ret = handle_g2v_notification(vgpu, data);
+		handle_g2v_notification(vgpu, data);
 		break;
 	/* add xhot and yhot to handled list to avoid error log */
 	case _vgtif_reg(cursor_x_hot):
@@ -1282,13 +1279,19 @@ static int pvinfo_mmio_write(struct intel_vgpu *vgpu, unsigned int offset,
 	case _vgtif_reg(execlist_context_descriptor_hi):
 		break;
 	case _vgtif_reg(rsv5[0])..._vgtif_reg(rsv5[3]):
+		invalid_write = true;
 		enter_failsafe_mode(vgpu, GVT_FAILSAFE_INSUFFICIENT_RESOURCE);
 		break;
 	default:
+		invalid_write = true;
 		gvt_vgpu_err("invalid pvinfo write offset %x bytes %x data %x\n",
 				offset, bytes, data);
 		break;
 	}
+
+	if (!invalid_write)
+		write_vreg(vgpu, offset, p_data, bytes);
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b69440cf41ea..75105a2c59ea 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12005,9 +12005,6 @@ intel_compare_link_m_n(const struct intel_link_m_n *m_n,
 			      m2_n2->gmch_m, m2_n2->gmch_n, !adjust) &&
 	    intel_compare_m_n(m_n->link_m, m_n->link_n,
 			      m2_n2->link_m, m2_n2->link_n, !adjust)) {
-		if (adjust)
-			*m2_n2 = *m_n;
-
 		return true;
 	}
 
@@ -13149,6 +13146,33 @@ static int calc_watermark_data(struct intel_atomic_state *state)
 	return 0;
 }
 
+static void intel_crtc_check_fastset(struct intel_crtc_state *old_crtc_state,
+				     struct intel_crtc_state *new_crtc_state)
+{
+	struct drm_i915_private *dev_priv =
+		to_i915(new_crtc_state->base.crtc->dev);
+
+	if (!intel_pipe_config_compare(dev_priv, old_crtc_state,
+				       new_crtc_state, true))
+		return;
+
+	new_crtc_state->base.mode_changed = false;
+	new_crtc_state->update_pipe = true;
+
+	/*
+	 * If we're not doing the full modeset we want to
+	 * keep the current M/N values as they may be
+	 * sufficiently different to the computed values
+	 * to cause problems.
+	 *
+	 * FIXME: should really copy more fuzzy state here
+	 */
+	new_crtc_state->fdi_m_n = old_crtc_state->fdi_m_n;
+	new_crtc_state->dp_m_n = old_crtc_state->dp_m_n;
+	new_crtc_state->dp_m2_n2 = old_crtc_state->dp_m2_n2;
+	new_crtc_state->has_drrs = old_crtc_state->has_drrs;
+}
+
 /**
  * intel_atomic_check - validate state object
  * @dev: drm device
@@ -13197,12 +13221,8 @@ static int intel_atomic_check(struct drm_device *dev,
 			return ret;
 		}
 
-		if (intel_pipe_config_compare(dev_priv,
-					to_intel_crtc_state(old_crtc_state),
-					pipe_config, true)) {
-			crtc_state->mode_changed = false;
-			pipe_config->update_pipe = true;
-		}
+		intel_crtc_check_fastset(to_intel_crtc_state(old_crtc_state),
+					 pipe_config);
 
 		if (needs_modeset(crtc_state))
 			any_ms = true;