From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751680AbaHTIjB (ORCPT ); Wed, 20 Aug 2014 04:39:01 -0400 Received: from mail-we0-f169.google.com ([74.125.82.169]:52650 "EHLO mail-we0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbaHTIi6 (ORCPT ); Wed, 20 Aug 2014 04:38:58 -0400 Message-ID: <53F45E9C.2080904@redhat.com> Date: Wed, 20 Aug 2014 10:38:52 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: David Matlack , Xiao Guangrong CC: Gleb Natapov , Avi Kivity , mtosatti@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: fix cache stale memslot info with correct mmio generation number References: <1407999713-3726-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <53F20653.2030204@redhat.com> <9AD43423-2FF3-422D-A5AD-61CAE6339CCC@linux.vnet.ibm.com> <53F24A49.2010807@redhat.com> <53F2C997.6070605@linux.vnet.ibm.com> <53F30AA4.4050803@redhat.com> <53F30FCD.3080109@linux.vnet.ibm.com> <53F312CE.9090004@redhat.com> <53F3EBEE.1030107@linux.vnet.ibm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 20/08/2014 03:03, David Matlack ha scritto: > On Tue, Aug 19, 2014 at 5:29 PM, Xiao Guangrong > wrote: >> On 08/19/2014 05:03 PM, Paolo Bonzini wrote: >>> Il 19/08/2014 10:50, Xiao Guangrong ha scritto: >>>> Okay, what confused me it that it seems that the single line patch >>>> is ok to you. :) >>> >>> No, it was late and I was confused. :) >>> >>>> Now, do we really need to care the case 2? like David said: >>>> "Sorry I didn't explain myself very well: Since we can get a single wrong >>>> mmio exit no matter what, it has to be handled in userspace. So my point >>>> was, it doesn't really help to fix that one very specific way that it can >>>> happen, because it can just happen in other ways. (E.g. update memslots >>>> occurs after is_noslot_pfn() and before mmio exit)." >>>> >>>> What's your idea? >>>> >>>>> I think if you always treat the low bit as zero in mmio sptes, you can >>>>> do that without losing a bit of the generation. >>>> >>>> What's you did is avoiding cache a invalid generation number into spte, but >>>> actually if we can figure it out when we check mmio access, it's ok. Like the >>>> updated patch i posted should fix it, that way avoids doubly increase the number. >>> >>> Yes. >>> >>>> Okay, if you're interested increasing the number doubly, there is the simpler >>>> one: >>> >>> This wastes a bit in the mmio spte though. My idea is to increase the >>> memslots generation twice, but drop the low bit in the mmio spte. >> >> Yeah, really smart idea. :) >> >> Paolo/David, would you mind making a patch for this (+ the comments in David's >> patch)? > > Paolo, since it was your idea would you like to write it? I don't mind either > way. Sure, I'll post the patch for review. Paolo