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# hv_vcpu_set_msr_access(_:_:_:)

Controls the guest access of a managed Model-Specific Register (MSR).

```
func hv_vcpu_set_msr_access(_ vcpu: hv_vcpuid_t, _ msr: UInt32, _ flags: hv_msr_flags_t) -> hv_return_t
```

## Parameters

`vcpu`

The instance of the vCPU.

`msr`

The ID of the MSR.

`flags`

The permission for `msr`.

## Return Value

[`HV_SUCCESS`](/documentation/Hypervisor/HV_SUCCESS) if the operation was successful, otherwise an error code specified in [`hv_return_t`](/documentation/Hypervisor/hv_return_t).

## Discussion

This function must be called by the owning thread.

---

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