Re: [PATCH v2] KVM: nVMX: Add support for rdtscp

[Bandan Das <bsd@redhat.com>]

Jan Kiszka <jan.kiszka@web.de> writes:

> On 2015-03-23 18:01, Bandan Das wrote:
>> Jan Kiszka <jan.kiszka@web.de> writes:
>> ...
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -2467,6 +2467,7 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>>>  	vmx->nested.nested_vmx_secondary_ctls_low = 0;
>>>  	vmx->nested.nested_vmx_secondary_ctls_high &=
>>>  		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
>>> +		SECONDARY_EXEC_RDTSCP |
>>>  		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
>>>  		SECONDARY_EXEC_APIC_REGISTER_VIRT |
>>>  		SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
>>> @@ -7510,7 +7511,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
>>>  		return nested_cpu_has(vmcs12, CPU_BASED_INVLPG_EXITING);
>>>  	case EXIT_REASON_RDPMC:
>>>  		return nested_cpu_has(vmcs12, CPU_BASED_RDPMC_EXITING);
>>> -	case EXIT_REASON_RDTSC:
>>> +	case EXIT_REASON_RDTSC: case EXIT_REASON_RDTSCP:
>>>  		return nested_cpu_has(vmcs12, CPU_BASED_RDTSC_EXITING);
>>>  	case EXIT_REASON_VMCALL: case EXIT_REASON_VMCLEAR:
>>>  	case EXIT_REASON_VMLAUNCH: case EXIT_REASON_VMPTRLD:
>>> @@ -8517,6 +8518,9 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>>>  						exec_control);
>>>  			}
>>>  		}
>>> +		if (!vmx->rdtscp_enabled)
>>> +			vmx->nested.nested_vmx_secondary_ctls_high &=
>>> +				~SECONDARY_EXEC_RDTSCP;
>> No need to do this if nested is not enabled ? Or just
>> a "if (nested)" in the prior if else loop should be enough I think.
>
> I can add this - but this is far away from being a hotpath. What would
> be the benefit?

Right, definitely not a hotpath, just seems unnecessary if nested is not enabled.

Bandan
> Thanks,
> Jan