Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964919AbdGTTQk (ORCPT ); Thu, 20 Jul 2017 15:16:40 -0400 Received: from mail-wm0-f53.google.com ([74.125.82.53]:37552 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753659AbdGTTQi (ORCPT ); Thu, 20 Jul 2017 15:16:38 -0400 MIME-Version: 1.0 In-Reply-To: References: <1496460115-12654-1-git-send-email-wanpeng.li@hotmail.com> <2ba5e53d-14f4-14a1-0084-a8b521a3ec3e@redhat.com> From: Jim Mattson Date: Thu, 20 Jul 2017 12:16:36 -0700 Message-ID: Subject: Re: [PATCH] KVM: nVMX: Fix exception injection To: Wanpeng Li Cc: Paolo Bonzini , "linux-kernel@vger.kernel.org" , kvm , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , 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-Length: 3956 Lines: 88 On Wed, Jul 19, 2017 at 7:31 PM, Wanpeng Li wrote: > Hi Jim, > 2017-07-19 2:47 GMT+08:00 Jim Mattson : >> Why do we expect the VM_EXIT_INTR_INFO and EXIT_QUALIFICATION fields >> of the VMCS to have the correct values for the injected exception? > > Good point, I think we should synthesize VM_EXIT_INTR_INFO and > EXIT_QUALIFICATION manually, I will post a patch for it. Btw, how > about setting EXIT_QULIFICATION to vcpu->arch.cr2 for the page fault > exception and 0 for other exceptions? >From the SDM, section 27.1: If an event causes a VM exit directly, it does not update architectural state as it would have if it had it not caused the VM exit: - A debug exception does not update DR6, DR7.GD, or IA32_DEBUGCTL.LBR. (Information about the nature of the debug exception is saved in the exit qualification field.) - A page fault does not update CR2. (The linear address causing the page fault is saved in the exit-qualification field.) This means that vcpu->arch.cr2 should not be set at this point for a #PF injection (and vcpu->arch.dr6 should not be set at this point for a #DB injection). For all other exceptions, yes, the exit qualification should be cleared. > > Regards, > Wanpeng Li > >> >> On Mon, Jun 5, 2017 at 5:19 AM, Wanpeng Li wrote: >>> 2017-06-05 20:07 GMT+08:00 Paolo Bonzini : >>>> >>>> >>>> On 03/06/2017 05:21, Wanpeng Li wrote: >>>>> Commit 0b6ac343fc (KVM: nVMX: Correct handling of exception injection) mentioned >>>>> that "KVM wants to inject page-faults which it got to the guest. This function >>>>> assumes it is called with the exit reason in vmcs02 being a #PF exception". >>>>> Commit e011c663 (KVM: nVMX: Check all exceptions for intercept during delivery to >>>>> L2) allows to check all exceptions for intercept during delivery to L2. However, >>>>> there is no guarantee the exit reason is exception currently, when there is an >>>>> external interrupt occurred on host, maybe a time interrupt for host which should >>>>> not be injected to guest, and somewhere queues an exception, then the function >>>>> nested_vmx_check_exception() will be called and the vmexit emulation codes will >>>>> try to emulate the "Acknowledge interrupt on exit" behavior, the warning is >>>>> triggered. >>>>> >>>>> This patch fixes it by confirming to inject exception to the guest when the exit >>>>> reason in vmcs02 is exception. >>>> >>>> I am confused. On one hand, the comment originally "this is the only >>>> case in which KVM injects a #PF when L2 is running", but I'm not sure >>>> it's true. For example, KVM could emulate a movs while running L2. If >>>> the source is MMIO and the destination is a missing page, the original >>>> failure could be an EPT misconfig, but the access to the destination >>>> would cause a #PF in the guest (could be a nice testcase for >>>> kvm-unit-tests, BTW :)). >>>> >>>> On the other hand, why would you reuse to_vmx(vcpu)->exit_reason in >>>> nested_vmx_check_exception? Would the following fix the bug: >>>> >>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>> index 9b4b5d6dcd34..ca5d2b93385c 100644 >>>> --- a/arch/x86/kvm/vmx.c >>>> +++ b/arch/x86/kvm/vmx.c >>>> @@ -2425,7 +2425,7 @@ static int nested_vmx_check_exception(struct >>>> kvm_vcpu *vcpu, unsigned nr) >>>> if (!(vmcs12->exception_bitmap & (1u << nr))) >>>> return 0; Here, we should consult vmcs12->page_fault_error_code_mask and vmcs12->page_fault_error_code_match when nr==PF_VECTOR, as in nested_vmx_is_page_fault_vmexit(). >>>> >>>> - nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason, >>>> + nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI, >>>> vmcs_read32(VM_EXIT_INTR_INFO), >>>> vmcs_readl(EXIT_QUALIFICATION)); >>>> return 1; >>>> >>> >>> You are right. >>> >>> Regards, >>> Wanpeng Li