Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968494AbdDTGrT (ORCPT ); Thu, 20 Apr 2017 02:47:19 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:47772 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S942309AbdDTGlB (ORCPT ); Thu, 20 Apr 2017 02:41:01 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ladi Prosek , "Michael S. Tsirkin" Subject: [PATCH 3.18 110/124] virtio_balloon: init 1st buffer in stats vq Date: Thu, 20 Apr 2017 08:36:25 +0200 Message-Id: <20170420063601.284149405@linuxfoundation.org> X-Mailer: git-send-email 2.12.2 In-Reply-To: <20170420063557.021306233@linuxfoundation.org> References: <20170420063557.021306233@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1868 Lines: 51 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ladi Prosek commit fc8653228c8588a120f6b5dad6983b7b61ff669e upstream. When init_vqs runs, virtio_balloon.stats is either uninitialized or contains stale values. The host updates its state with garbage data because it has no way of knowing that this is just a marker buffer used for signaling. This patch updates the stats before pushing the initial buffer. Alternative fixes: * Push an empty buffer in init_vqs. Not easily done with the current virtio implementation and violates the spec "Driver MUST supply the same subset of statistics in all buffers submitted to the statsq". * Push a buffer with invalid tags in init_vqs. Violates the same spec clause, plus "invalid tag" is not really defined. Note: the spec says: When using the legacy interface, the device SHOULD ignore all values in the first buffer in the statsq supplied by the driver after device initialization. Note: Historically, drivers supplied an uninitialized buffer in the first buffer. Unfortunately QEMU does not seem to implement the recommendation even for the legacy interface. Signed-off-by: Ladi Prosek Signed-off-by: Michael S. Tsirkin Signed-off-by: Greg Kroah-Hartman --- drivers/virtio/virtio_balloon.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -355,6 +355,8 @@ static int init_vqs(struct virtio_balloo * Prime this virtqueue with one buffer so the hypervisor can * use it to signal us later (it can't be broken yet!). */ + update_balloon_stats(vb); + sg_init_one(&sg, vb->stats, sizeof vb->stats); if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL) < 0)