hv_vcpu_set_tsc_relative(_:_:)
Sets the offset of the guest timestamp-counter (TSC) relative to the Hypervisor’s TSC clock.
Declaration
func hv_vcpu_set_tsc_relative(_ vcpu: hv_vcpuid_t, _ offset: Int64) -> hv_return_tParameters
- vcpu:
The vCPU ID.
- offset:
The relative offset value to apply to VMCS TSC-offset field.
Return Value
0 on success, or an hv_return_t error code.
Discussion
Use this function to set the TSC-offset field in the VMCS so that the TSC value in the guest is the value of hv_tsc_clock() plus the given offset. The examples below show simple ways to calculate and set the TSC offset:
// initialization - set guest TSC to zero
int64_t vtsc_offset = - scale * hv_tsc_clock();
hv_vcpu_tsc_relative_offset(vcpu, vtsc_offset);
// compute the guest TSC at runtime from the host
uint64_t vtsc = scale * hv_tsc_clock() + vtsc_offset;
// guest writing to the IA32_TSC MSR
vtsc_offset = newTSCvalue - scale * hv_tsc_clock();
hv_vcpu_tsc_relative_offset(vcpu, vtsc_offset);
// guest writing to the IA32_TSC_ADJUST MSR
vtsc_offset += adjustment;
hv_vcpu_tsc_relative_offset(vcpu, vtsc_offset);
// at entry to inner hypervisor
hv_vcpu_tsc_relative_offset(vcpu, vtsc_offset);
// at entry to inner guest
hv_vcpu_tsc_relative_offset(vcpu, vtsc_offset + nested_offset);