From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH] KVM: SVM: fix random segfaults with NPT enabled Date: Thu, 28 Aug 2008 17:58:25 +0200 Message-ID: <20080828155825.GB4895@8bytes.org> References: <20080827135731.GC26059@amd.com> <48B57126.7000603@qumranet.com> <20080827153550.GB3801@8bytes.org> <48B577C3.3050302@qumranet.com> <20080827162715.GA28498@amd.com> <48B58599.1040509@qumranet.com> <48B587EC.7020606@qumranet.com> <20080828145838.GA4971@amd.com> <48B6C12D.1020501@qumranet.com> <48B6C44F.2000201@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Joerg Rodel , kvm@vger.kernel.org, stable@kernel.org, Alexander Graf To: Avi Kivity Return-path: Received: from 8bytes.org ([88.198.83.132]:59795 "EHLO 8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751471AbYH1P60 (ORCPT ); Thu, 28 Aug 2008 11:58:26 -0400 Content-Disposition: inline In-Reply-To: <48B6C44F.2000201@qumranet.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Aug 28, 2008 at 06:29:19PM +0300, Avi Kivity wrote: > Avi Kivity wrote: > > Joerg Rodel wrote: > > > >> I did a bit meditation about the softmmu code today. In the path of the > >> NPT fault the function kvm_mmu_free_some_pages() is called which itself > >> calls kvm_mmu_zap_page(). There the two functions > >> kvm_mmu_page_unlink_children() and kvm_mmu_unlink_parents() are called. > >> They both call mmu_page_remove_parent_pte() which modifies ptes. But > >> only the first function, kvm_mmu_page_unlink_children(), flushes remote > >> TLBs. The function kvm_mmu_unlink_parents() does not. Is this correct? > >> > >> > >> > > > > It isn't correct. I'll move the flush below. Good catch. > > > > However, I can't believe this is responsible. There is very little page > > zapping going on with npt. > > > > > > Indeed, the mmu_shadow_zapped counter for the guest I'm testing is zero, > so this code path was never hit. Ok, but at least we found another missing flush :) Joerg