From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: nVMX: Shadowing of CPU_BASED_VM_EXEC_CONTROL broken Date: Thu, 9 Oct 2014 07:58:08 +0800 Message-ID: <20141008235808.GA17971@kernel> References: <5434F5F9.3030803@siemens.com> <20141008092539.GA16561@kernel> <5435092A.3090704@siemens.com> <54350FD4.10403@redhat.com> <543511FE.3060108@siemens.com> <54351336.4030005@redhat.com> <54355344.5050301@siemens.com> <20141008233447.GA17692@kernel> Reply-To: Wanpeng Li Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm , Bandan Das To: Jan Kiszka , Paolo Bonzini Return-path: Received: from mga14.intel.com ([192.55.52.115]:6122 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753478AbaJIASs (ORCPT ); Wed, 8 Oct 2014 20:18:48 -0400 Content-Disposition: inline In-Reply-To: <20141008233447.GA17692@kernel> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Oct 09, 2014 at 07:34:47AM +0800, Wanpeng Li wrote: >On Wed, Oct 08, 2014 at 05:07:48PM +0200, Jan Kiszka wrote: >>On 2014-10-08 12:34, Paolo Bonzini wrote: >>> Il 08/10/2014 12:29, Jan Kiszka ha scritto: >>>>>> But it would write to the vmcs02, not to the shadow VMCS; the shadow >>>>>> VMCS is active during copy_shadow_to_vmcs12/copy_vmcs12_to_shadow, and >>>>>> at no other time. It is not clear to me how the VIRTUAL_INTR_PENDING >>>>>> bit ended up from the vmcs02 (where it is perfectly fine) to the vmcs12. >>>> Well, but somehow that bit ends up in vmcs12, that's a fact. Also that >>>> the proble disappears when shadowing is disabled. Need to think about >>>> the path again. Maybe there is just a bug, not a conceptual issue. >>> >>> Yeah, and at this point we cannot actually exclude a processor bug. Can >>> you check that the bit is not in the shadow VMCS just before vmrun, or >>> just after enable_irq_window? >>> >>> Having a kvm-unit-tests testcase could also be of some help. >> >>As usual, this was a nasty race that involved some concurrent VCPUs and >>proper host load, so hard to write unit tests... >> >>diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>index 04fa1b8..d6bcaca 100644 >>--- a/arch/x86/kvm/vmx.c >>+++ b/arch/x86/kvm/vmx.c >>@@ -6417,6 +6417,8 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) >> const unsigned long *fields = shadow_read_write_fields; >> const int num_fields = max_shadow_read_write_fields; >> >>+ preempt_disable(); >>+ >> vmcs_load(shadow_vmcs); >> >> for (i = 0; i < num_fields; i++) { >>@@ -6440,6 +6442,8 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) >> >> vmcs_clear(shadow_vmcs); >> vmcs_load(vmx->loaded_vmcs->vmcs); >>+ >>+ preempt_enable(); >> } >> >> static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >>@@ -6457,6 +6461,8 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >> u64 field_value = 0; >> struct vmcs *shadow_vmcs = vmx->nested.current_shadow_vmcs; >> >>+ preempt_disable(); >>+ >> vmcs_load(shadow_vmcs); >> >> for (q = 0; q < ARRAY_SIZE(fields); q++) { >>@@ -6483,6 +6489,8 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) >> >> vmcs_clear(shadow_vmcs); >> vmcs_load(vmx->loaded_vmcs->vmcs); >>+ >>+ preempt_enable(); >> } >> >> /* >> >>No proper patch yet because there might be a smarter approach without >>using the preempt_disable() hammer. But the point is that we temporarily >>load a vmcs without updating loaded_vmcs->vmcs. Now, if some other VCPU >>is scheduling in right in the middle of this, the wrong vmcs will be >>flushed and then reloaded - e.g. a non-shadow vmcs with that interrupt >>window flag set... > >If non-shadow vmcs and shadow vmcs can present in one system simultaneously? Ah, got it, you mean non-current-shadow vmcs. Regards, Wanpeng Li > >Regards, >Wanpeng Li > >> >>Patch is currently under heavy load testing here, but it looks very good >>as the bug was quickly reproducible before I applied it. >> >>Jan >> >>-- >>Siemens AG, Corporate Technology, CT RTC ITP SES-DE >>Corporate Competence Center Embedded Linux >>-- >>To unsubscribe from this list: send the line "unsubscribe kvm" in >>the body of a message to majordomo@vger.kernel.org >>More majordomo info at http://vger.kernel.org/majordomo-info.html >-- >To unsubscribe from this list: send the line "unsubscribe kvm" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html