Re: [PATCH v4 17/17] kvm: vmx: Emulate TEST_CTL MSR

[Paolo Bonzini]

On 11/03/19 16:10, Xiaoyao Li wrote:
> On Mon, 2019-03-11 at 14:31 +0100, Paolo Bonzini wrote:
>> On 09/03/19 03:31, Xiaoyao Li wrote:
>>> Hi, Paolo,
>>>
>>> Do you have any comments on this patch?
>>>
>>> We are preparing v5 patches for split lock detection, if you have any
>>> comments
>>> about this one, please let me know.
>>
>> No, my only comment is that it should be placed _before_ the other two
>> for bisectability.  I think I have already sent that small remark.
>>
>> Thanks,
>>
>> Paolo
> 
> I cannot find the small remark you sent before. Maybe I missed something.
> But I'am confused why it should be placed _before_ the other two. This patch
> just use the vmx->core_capability that defined it the previous patch.

Because otherwise the guest can see core_capability != 0 and will #GP
when trying to use split lock detection.

But you are right, this patch must be the last.  Instead,
kvm-get_core_capability() should always return  0 until the previous
patch.  Then in this patch you add the rdmsr and boot_cpu_has() tests.

Paolo

>>>> +		if (!(vmx->core_capability & CORE_CAP_SPLIT_LOCK_DETECT))
>>>> +			return 1;
>>>> +
>>>> +		if (data & ~TEST_CTL_ENABLE_SPLIT_LOCK_DETECT)
>>>> +			return 1;
>>>> +		vmx->msr_test_ctl = data;
>>>> +		break;
>>>>  	case MSR_EFER:
>>>>  		ret = kvm_set_msr_common(vcpu, msr_info);
>>>>  		break;
>>>> @@ -4108,6 +4122,9 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
>>>>  
>>>>  	vmx->arch_capabilities = kvm_get_arch_capabilities();
>>>>  
>>>> +	/* disable AC split lock by default */
>>>> +	vmx->msr_test_ctl = 0;
>>>> +
>>>>  	vm_exit_controls_init(vmx, vmx_vmexit_ctrl());
>>>>  
>>>>  	/* 22.2.1, 20.8.1 */
>>>> @@ -4145,6 +4162,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu,
>>>> bool
>>>> init_event)
>>>>  
>>>>  	vmx->rmode.vm86_active = 0;
>>>>  	vmx->spec_ctrl = 0;
>>>> +	vmx->msr_test_ctl = 0;
>>>>  
>>>>  	vcpu->arch.microcode_version = 0x100000000ULL;
>>>>  	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
>>>> @@ -6344,6 +6362,21 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx
>>>> *vmx)
>>>>  					msrs[i].host, false);
>>>>  }
>>>>  
>>>> +static void atomic_switch_msr_test_ctl(struct vcpu_vmx *vmx)
>>>> +{
>>>> +	u64 host_msr_test_ctl;
>>>> +
>>>> +	if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
>>>> +		return;
>>>> +
>>>> +	rdmsrl(MSR_TEST_CTL, host_msr_test_ctl);
>>>> +	if (host_msr_test_ctl == vmx->msr_test_ctl)
>>>> +		clear_atomic_switch_msr(vmx, MSR_TEST_CTL);
>>>> +	else
>>>> +		add_atomic_switch_msr(vmx, MSR_TEST_CTL, vmx->msr_test_ctl,
>>>> +				      host_msr_test_ctl, false);
>>>> +}
>>>> +
>>>>  static void vmx_arm_hv_timer(struct vcpu_vmx *vmx, u32 val)
>>>>  {
>>>>  	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, val);
>>>> @@ -6585,6 +6618,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>>>>  
>>>>  	atomic_switch_perf_msrs(vmx);
>>>>  
>>>> +	atomic_switch_msr_test_ctl(vmx);
>>>> +
>>>>  	vmx_update_hv_timer(vcpu);
>>>>  
>>>>  	/*
>>>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
>>>> index cc22379991f3..e8831609c6c3 100644
>>>> --- a/arch/x86/kvm/vmx/vmx.h
>>>> +++ b/arch/x86/kvm/vmx/vmx.h
>>>> @@ -191,6 +191,7 @@ struct vcpu_vmx {
>>>>  	u64		      msr_guest_kernel_gs_base;
>>>>  #endif
>>>>  
>>>> +	u64		      msr_test_ctl;
>>>>  	u64		      core_capability;
>>>>  	u64		      arch_capabilities;
>>>>  	u64		      spec_ctrl;
>>
>>
>