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ERROR_HV_INVALID_HYPERCALL_INPUT
Control-word validation, not an API argument error
The hypercall code may be valid while the 64-bit control value is not. Hyper-V documents this status for invalid rep-call bookkeeping, reserved bits that are not zero, and incompatible control fields. For example, a non-rep call cannot carry a non-zero rep count, a rep call needs a valid count and start index, and a variable-header size is allowed only for calls that explicitly support it.
This differs from ERROR_HV_INVALID_PARAMETER, which is returned by a particular hypercall after its own operation-specific arguments are checked. It also differs from ERROR_HV_INVALID_ALIGNMENT, which concerns guest-physical parameter-block placement.
What to validate
- Decode the control word into call code, fast-call flag, variable-header size, rep count and rep start index.
- Clear every field documented as reserved-zero; do not reuse a stale control word as a template.
- For a rep hypercall, ensure the start index is less than the count and resume it using the progress returned by Hyper-V.
- Use the call-specific input layout for the negotiated architecture and interface revision.
Microsoft Hyper-V TLFS: control value and common status codes · Hypervisor Top Level Functional Specification
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