Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751537AbaJQKPg (ORCPT ); Fri, 17 Oct 2014 06:15:36 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:47611 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751238AbaJQKPf (ORCPT ); Fri, 17 Oct 2014 06:15:35 -0400 X-IronPort-AV: E=Sophos;i="5.04,738,1406592000"; d="scan'208";a="183488208" Message-ID: <5440EC45.1020205@citrix.com> Date: Fri, 17 Oct 2014 11:15:33 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0 MIME-Version: 1.0 To: Juergen Gross , David Vrabel , , , Subject: Re: [Xen-devel] [PATCH] xen: avoid race in p2m handling References: <1413439997-32344-1-git-send-email-jgross@suse.com> <543FE940.60901@citrix.com> <544099B1.4090202@suse.com> In-Reply-To: <544099B1.4090202@suse.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/10/14 05:23, Juergen Gross wrote: > On 10/16/2014 05:50 PM, David Vrabel wrote: >> On 16/10/14 07:13, Juergen Gross wrote: >>> When a new p2m leaf is allocated this leaf is linked into the p2m tree >>> via cmpxchg. Unfortunately the compare value for checking the success >>> of the update is read after checking for the need of a new leaf. It is >>> possible that a new leaf has been linked into the tree concurrently >>> in between. This could lead to a leaked memory page and to the loss of >>> some p2m entries. >>> >>> Avoid the race by using the read compare value for checking the need >>> of a new p2m leaf. >> [...] >>> @@ -579,11 +580,10 @@ static bool alloc_p2m(unsigned long pfn) >>> } >>> } >>> >>> - if (p2m_top[topidx][mididx] == p2m_identity || >>> - p2m_top[topidx][mididx] == p2m_missing) { >>> + p2m_orig = p2m_top[topidx][mididx]; >> >> Do you need to use ACCESS_ONCE() here? > > Yes, you are probably right. Should I send a new patch or do you want > to modify it? Can you go through and see if there are any other places in the p2m code that also need ACCESS_ONCE()? And then repost, thanks! David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/