Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753751Ab3FILoL (ORCPT ); Sun, 9 Jun 2013 07:44:11 -0400 Received: from mail-oa0-f47.google.com ([209.85.219.47]:56039 "EHLO mail-oa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752958Ab3FILoJ (ORCPT ); Sun, 9 Jun 2013 07:44:09 -0400 Message-ID: <51B46A83.4010008@gmail.com> Date: Sun, 09 Jun 2013 19:44:03 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Gleb Natapov CC: Paolo Bonzini , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH] KVM: x86: fix missed memory synchronization when patch hypercall References: <51B2A1D9.6060306@gmail.com> <20130609084526.GH4725@redhat.com> <51B44B01.7050304@gmail.com> <20130609093910.GL4725@redhat.com> <51B45289.6080704@gmail.com> <20130609101934.GN4725@redhat.com> <51B4661D.8080807@gmail.com> <20130609113624.GQ4725@redhat.com> In-Reply-To: <20130609113624.GQ4725@redhat.com> 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 Content-Length: 3924 Lines: 97 On 06/09/2013 07:36 PM, Gleb Natapov wrote: > On Sun, Jun 09, 2013 at 07:25:17PM +0800, Xiao Guangrong wrote: >> On 06/09/2013 06:19 PM, Gleb Natapov wrote: >>> On Sun, Jun 09, 2013 at 06:01:45PM +0800, Xiao Guangrong wrote: >>>> On 06/09/2013 05:39 PM, Gleb Natapov wrote: >>>>> On Sun, Jun 09, 2013 at 05:29:37PM +0800, Xiao Guangrong wrote: >>>>>> On 06/09/2013 04:45 PM, Gleb Natapov wrote: >>>>>> >>>>>>> +static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt) >>>>>>> +{ >>>>>>> + struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); >>>>>>> + return kvm_exec_with_stopped_vcpu(vcpu->kvm, >>>>>>> + emulator_fix_hypercall_cb, ctxt); >>>>>>> +} >>>>>>> + >>>>>>> + >>>>>>> /* >>>>>>> * Check if userspace requested an interrupt window, and that the >>>>>>> * interrupt window is open. >>>>>>> @@ -5761,6 +5769,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) >>>>>>> kvm_deliver_pmi(vcpu); >>>>>>> if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu)) >>>>>>> vcpu_scan_ioapic(vcpu); >>>>>>> + if (kvm_check_request(KVM_REQ_STOP_VCPU, vcpu)){ >>>>>>> + mutex_lock(&vcpu->kvm->lock); >>>>>>> + mutex_unlock(&vcpu->kvm->lock); >>>>>> >>>>>> We should execute a serializing instruction here? >>>>>> >>>>>>> --- a/virt/kvm/kvm_main.c >>>>>>> +++ b/virt/kvm/kvm_main.c >>>>>>> @@ -222,6 +222,18 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm) >>>>>>> make_all_cpus_request(kvm, KVM_REQ_SCAN_IOAPIC); >>>>>>> } >>>>>>> >>>>>>> +int kvm_exec_with_stopped_vcpu(struct kvm *kvm, int (*cb)(void *), void *data) >>>>>>> +{ >>>>>>> + int r; >>>>>>> + >>>>>>> + mutex_lock(&kvm->lock); >>>>>>> + make_all_cpus_request(kvm, KVM_REQ_STOP_VCPU); >>>>>>> + r = cb(data); >>>>>> >>>>>> And here? >>>>> Since the serialisation instruction the SDM suggest to use is CPUID I >>>>> think the point here is to flush CPU pipeline. Since all vcpus are out >>>>> of a guest mode I think out of order execution of modified instruction >>>>> is no an issue here. >>>> >>>> I checked the SDM that it did not said VMLAUNCH/VMRESUME are the >>>> serializing instructions both in VM-Entry description and Instruction >>>> reference, instead it said the VMX related serializing instructions are: >>>> INVEPT, INVVPID. >>>> >>>> So, i guess the explicit serializing instruction is needed here. >>>> >>> Again the question is what for? SDM says: >>> >>> The Intel 64 and IA-32 architectures define several serializing >>> instructions. These instructions force the processor to complete all >>> modifications to flags, registers, and memory by previous instructions >>> and to drain all buffered writes to memory before the next instruction >>> is fetched and executed. >>> >>> So flags and registers modifications on a host are obviously irrelevant for a guest. >> >> Okay. Hmm... but what can guarantee that "drain all buffered writes to memory"? > Memory barrier should guaranty that as I said bellow. > >> >>> And for memory ordering we have smp_mb() on a guest entry. >> >> If i understand the SDM correctly, memory-ordering instructions can not drain >> instruction buffer, it only drains "data memory subsystem": > What is "instruction buffer"? I mean "Instruction Cache" (icache). Can memory ordering drain icache? The "data memory subsystem" confused me, does it mean dcache? > >> >> "The following instructions are memory-ordering instructions, not serializing instruc- >> tions. These drain the data memory subsystem. They do not serialize the instruction >> execution stream:" >> >> No? > Yes, but we have no issue with instruction execution stream as I said > above. No guest instruction can be in a pipeline while all vcpus are in > a host. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/