Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752270AbdFNNC1 (ORCPT ); Wed, 14 Jun 2017 09:02:27 -0400 Received: from mail-ot0-f173.google.com ([74.125.82.173]:33673 "EHLO mail-ot0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751726AbdFNNCZ (ORCPT ); Wed, 14 Jun 2017 09:02:25 -0400 MIME-Version: 1.0 In-Reply-To: <20170614125221.GA2343@potion> References: <1497334094-6982-1-git-send-email-wanpeng.li@hotmail.com> <1497334094-6982-4-git-send-email-wanpeng.li@hotmail.com> <20170613185522.GA29537@potion> <20170614125221.GA2343@potion> From: Wanpeng Li Date: Wed, 14 Jun 2017 21:02:24 +0800 Message-ID: Subject: Re: [PATCH 3/4] KVM: async_pf: Force a nested vmexit if the injected #PF is async_pf To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Cc: "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , Wanpeng Li Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v5ED2WGX003624 Content-Length: 1630 Lines: 41 2017-06-14 20:52 GMT+08:00 Radim Krčmář : > 2017-06-14 09:07+0800, Wanpeng Li: >> 2017-06-14 2:55 GMT+08:00 Radim Krčmář : >> > Using vcpu->arch.cr2 is suspicious as VMX doesn't update CR2 on VM >> > exits; isn't this going to change the CR2 visible in L2 guest after a >> > nested VM entry? >> >> Sorry, I don't fully understand the question. As you know this >> vcpu->arch.cr2 which includes token is set before async pf injection, > > Yes, I'm thinking that setting vcpu->arch.cr2 is a mistake in this case. > >> and L1 will intercept it from EXIT_QUALIFICATION during nested vmexit, > > Right, so we do not need to have the token in CR2, because L1 is not > going to look at it. > >> why it can change the CR2 visible in L2 guest after a nested VM entry? > > Sorry, the situation is too convoluted to be expressed in one sentence: > > 1) L2 is running with CR2 = L2CR2 > 3) VMX exits (say, unrelated EXTERNAL_INTERRUPT) and L0 stores L2CR2 in > vcpu->arch.cr2 > 2) APF for L1 has completed > 4) L0 KVM wants to inject APF and sets vcpu->arch.cr2 = APFT > 5) L0 KVM does a nested VM exit to L1, EXIT_QUALIFICATION = APFT > 6) L0 KVM enters L1 with CR2 = vcpu->arch.cr2 = APFT > 7) L1 stores APFT as L2's CR2 > 8) L1 handles APF, maybe reschedules, but eventually comes back to this > L2's thread > 9) after some time, L1 enters L2 with CR2 = APFT > 10) L2 is running with CR2 = APTF > > The original L2CR2 is lost and we'd introduce a bug if L2 wanted to look > at it, e.g. it was in a process of handling its #PF. Good point. What's your proposal? :) Regards, Wanpeng Li