From patchwork Wed Jan 6 12:08:28 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefano Stabellini X-Patchwork-Id: 7967881 Return-Path: X-Original-To: patchwork-xen-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id C64719F32E for ; Wed, 6 Jan 2016 12:11:30 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 0153B20173 for ; Wed, 6 Jan 2016 12:11:30 +0000 (UTC) Received: from lists.xen.org (lists.xenproject.org [50.57.142.19]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2CD782010E for ; Wed, 6 Jan 2016 12:11:29 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xen.org) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1aGmtd-0007uM-3Q; Wed, 06 Jan 2016 12:08:57 +0000 Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1aGmta-0007uH-Tv for xen-devel@lists.xensource.com; Wed, 06 Jan 2016 12:08:55 +0000 Received: from [193.109.254.147] by server-8.bemta-14.messagelabs.com id 66/A0-24450-6D30D865; Wed, 06 Jan 2016 12:08:54 +0000 X-Env-Sender: prvs=8066dafa4=Stefano.Stabellini@citrix.com X-Msg-Ref: server-8.tower-27.messagelabs.com!1452082132!11257970!1 X-Originating-IP: [66.165.176.63] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogNjYuMTY1LjE3Ni42MyA9PiAzMDYwNDg=\n, received_headers: No Received headers X-StarScan-Received: X-StarScan-Version: 7.35.1; banners=-,-,- X-VirusChecked: Checked Received: (qmail 22035 invoked from network); 6 Jan 2016 12:08:53 -0000 Received: from smtp02.citrix.com (HELO SMTP02.CITRIX.COM) (66.165.176.63) by server-8.tower-27.messagelabs.com with RC4-SHA encrypted SMTP; 6 Jan 2016 12:08:53 -0000 X-IronPort-AV: E=Sophos;i="5.20,528,1444694400"; d="scan'208";a="329313970" Date: Wed, 6 Jan 2016 12:08:28 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Message-ID: User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 X-DLP: MIA1 Cc: liuling-it@360.cn, xen-devel@lists.xensource.com, Stefano Stabellini Subject: [Xen-devel] [PATCH] xenfb.c: avoid expensive loops when prod <= out_cons X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP If the frontend sets out_cons to a value higher than out_prod, it will cause xenfb_handle_events to loop about 2^32 times. Avoid that by using better checks at the beginning of the function. Signed-off-by: Stefano Stabellini diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c index 4e2a27a..f963cf2 100644 --- a/hw/display/xenfb.c +++ b/hw/display/xenfb.c @@ -789,10 +789,11 @@ static void xenfb_handle_events(struct XenFB *xenfb) prod = page->out_prod; out_cons = page->out_cons; - if (prod == out_cons) - return; + if (prod <= out_cons) { + return; + } xen_rmb(); /* ensure we see ring contents up to prod */ - for (cons = out_cons; cons != prod; cons++) { + for (cons = out_cons; cons < prod; cons++) { union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons); uint8_t type = event->type; int x, y, w, h;