From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] KVM: SVM: fix random segfaults with NPT enabled Date: Wed, 27 Aug 2008 19:59:24 +0300 Message-ID: <48B587EC.7020606@qumranet.com> References: <1219839523-25677-1-git-send-email-joerg.roedel@amd.com> <48B55266.4000300@qumranet.com> <48B55C56.2060503@qumranet.com> <20080827135731.GC26059@amd.com> <48B57126.7000603@qumranet.com> <20080827153550.GB3801@8bytes.org> <48B577C3.3050302@qumranet.com> <20080827162715.GA28498@amd.com> <48B58599.1040509@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Joerg Roedel , kvm@vger.kernel.org, stable@kernel.org, Alexander Graf To: Joerg Rodel Return-path: Received: from il.qumranet.com ([212.179.150.194]:55187 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755409AbYH0Q70 (ORCPT ); Wed, 27 Aug 2008 12:59:26 -0400 In-Reply-To: <48B58599.1040509@qumranet.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > Joerg Rodel wrote: >>> Meanwhile, I applied the patch, but I'm very worried about this. >>> >> >> Yes, we are also worried. Another question is why this only happens with >> NPT. The SoftMMU code should also fail with shadow paging if there is a >> bug. >> > > Slightly different paths -- direct_map vs page_fault. Also, with npt, > all cpus will access the same pte that's being modified; without npt, > faults on the same page will result in different ptes being > instantiated, as each access will be from a different guest pte. > > Maybe we should turn on the dirty bit in the instantiated ptes -- that > will reduce the processor's mucking about with them. > I meant the accessed bit. The dirty bit is always set, but the accessed bit it not, due to a bug. Fixing it doesn't help, though. -- error compiling committee.c: too many arguments to function