From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756101AbcGGB6x (ORCPT ); Wed, 6 Jul 2016 21:58:53 -0400 Received: from mail-oi0-f53.google.com ([209.85.218.53]:33755 "EHLO mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751635AbcGGB6v (ORCPT ); Wed, 6 Jul 2016 21:58:51 -0400 MIME-Version: 1.0 In-Reply-To: <7ae48d13-5349-0b81-df2b-e14217feb8f2@redhat.com> References: <1467805375-4676-1-git-send-email-wanpeng.li@hotmail.com> <20160706132601.qxcn7sm365xf6pos@hz-desktop> <65eb56ae-c55d-cca4-d685-83413621bb9a@redhat.com> <20160706160322.kg3jbwztkfhl7gw5@hz-desktop> <7ae48d13-5349-0b81-df2b-e14217feb8f2@redhat.com> From: Wanpeng Li Date: Thu, 7 Jul 2016 09:58:50 +0800 Message-ID: Subject: Re: [PATCH v3] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest To: Paolo Bonzini Cc: "linux-kernel@vger.kernel.org" , kvm , Wanpeng Li , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Yunhong Jiang , Jan Kiszka , Jim Mattson Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2016-07-07 1:11 GMT+08:00 Paolo Bonzini : > > > On 06/07/2016 18:03, Haozhong Zhang wrote: >>>> This patch also fixed the crash of L1 Xen with L2 HVM guest. Xen does >>>> not enable preemption timer for HVM guests, and will get panic if it >>>> receives a preemption timer vmexit. >>> >>> Thanks! I'm still not sure why the bit is set in the vmcs02 though... >> >> Yes, it looks really weird. >> >> I replaced "return false" in Wanpeng's patch by >> >> pr_info("VMCS: preemption timer enabled = %d\n", >> !!(vmcs_read32(PIN_BASED_VM_EXEC_CONTROL) & PIN_BASED_VMX_PREEMPTION_TIMER)); >> >> and redid my test. As expected, L1 Xen crashed due to the unexpected >> preemption timer vmexit. I got a log from above statement just before crash: >> >> VMCS: preemption timer enabled = 1 >> >> which is expected to be 0, because preemption timer is disabled in >> vmcs02. I also modified L1 Xen to dump VMCS at crash, and it says >> preemption timer is disabled. >> >> I noticed Jim Mattson recently sent a patch "KVM: nVMX: Fix memory >> corruption when using VMCS shadowing" to fix the inconsistency between >> vmcs12 and its shadow. Is it relevant here? I'll test his patch >> tomorrow. > > No, it shouldn't have any effect. > > I think it happens when the post_block hook switches back from sw_timer > to hv_timer, and L2 is running. So the right fix should be along the > lines of what I posted earlier. If you don't beat me to it, I'll take > another look tomorrow. I think I just figure out the root cause, I will send out a patch to fix it. Regards, Wanpeng Li