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"? > 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": "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? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html