From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Rodel Subject: Re: [PATCH] KVM: SVM: fix random segfaults with NPT enabled Date: Wed, 27 Aug 2008 15:57:31 +0200 Message-ID: <20080827135731.GC26059@amd.com> References: <1219839523-25677-1-git-send-email-joerg.roedel@amd.com> <48B55266.4000300@qumranet.com> <48B55C56.2060503@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: kvm@vger.kernel.org, stable@kernel.org, Alexander Graf To: Avi Kivity Return-path: Received: from outbound-dub.frontbridge.com ([213.199.154.16]:52184 "EHLO IE1EHSOBE006.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758586AbYH0N62 (ORCPT ); Wed, 27 Aug 2008 09:58:28 -0400 Content-Disposition: inline In-Reply-To: <48B55C56.2060503@qumranet.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Aug 27, 2008 at 04:53:26PM +0300, Avi Kivity wrote: > Avi Kivity wrote: > >Joerg Rodel wrote: > >>From: Joerg Roedel > >> > >>This patch introduces a guest TLB flush on every NPF exit in KVM. This fixes > >>random segfaults and #UD exceptions in the guest seen under some workloads > >>(e.g. long running compile workloads or tbench). A kernbench run with and > >>without that fix showed that it has a slowdown lower than 0.5% > >> > >> > > > >hm. tbench doesn't allocate memory, so there shouldn't be any npt faults. I don't > >see how this can make a difference. > > > >It can only change something if X is started and we're tracking writes to the > >framebuffer. Is this the case? > > > > I fixed a missing flush in this area. Does it help? (I doubt it). Can you post > instructions on how to reproduce? I will test it. Is the fix in your latest kernel.org tree? Reproduce it with a KVM guest and start tbench in it with around 100 clients configured. The tbench-process will crash when the bug is hit. Joerg -- | AMD Saxony Limited Liability Company & Co. KG Operating | Wilschdorfer Landstr. 101, 01109 Dresden, Germany System | Register Court Dresden: HRA 4896 Research | General Partner authorized to represent: Center | AMD Saxony LLC (Wilmington, Delaware, US) | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy