# hv_vcpu_set_sme_za_reg(_:_:_:) Sets the value of the vCPU ZA matrix register in streaming Scalable Vector Extension (SVE) mode. ``` func hv_vcpu_set_sme_za_reg(_ vcpu: hv_vcpu_t, _ value: UnsafePointer, _ length: Int) -> hv_return_t ``` ## Parameters `vcpu` The ID of the vCPU instance. `value` A pointer to the register value to set. `length` The length of the provided ZA register value, in bytes. ## Return Value `HV_SUCCESS` on success, an error code otherwise. ## Discussion This method returns an error if `PSTATE.ZA` is `0` (for example, if [`za_storage_enabled`](/documentation/Hypervisor/hv_vcpu_sme_state_t/za_storage_enabled) is `false`), or if the value `length` isn’t the range of [maximum of `SVL` bytes * maximum `SVL` bytes]. This methods doesn’t require streaming SVE mode to be in an enabled state. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)