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Setting the PCI Configuration Data of a Virtual Function

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The miniport driver for a PCI Express (PCIe) Virtual Function (VF) runs in the guest operating system of a Hyper-V child partition. Because of this, the VF miniport driver cannot directly access hardware resources, such as the VF's PCI configuration space. Only the miniport driver for the PCIe Physical Function (PF) can access the PCI configuration space for a VF. The PF miniport driver runs in the management operating system of a Hyper-V parent partition and has privileged access to the VF resources.

The overlying driver, such as the virtualization stack, issues the OID set request of OID_SRIOV_WRITE_VF_CONFIG_SPACE when the VF miniport driver calls NdisMSetBusData to write to its PCI configuration space.

Before it issues this OID set request, the overlying driver must set the members of theNDIS_SRIOV_WRITE_VF_CONFIG_SPACE_PARAMETERS structure in the following way:

  • Set the VFId member to the identifier of the VF for which the information is to be written.

  • Set the Offset member to the offset within the PCI configuration space of the VF in which data will be written.

  • Set the Length member to the number of bytes to write to the VF's PCI configuration space.

  • Set the BufferOffset member to the offset within the buffer (referenced by theInformationBuffer member) that will contain the data that is written to the specified VF's PCI configuration space. This offset is specified in units of bytes from the beginning of the NDIS_SRIOV_WRITE_VF_CONFIG_SPACE_PARAMETERS structure.

When it handles the OID method request of OID_SRIOV_WRITE_VF_CONFIG_SPACE, the PF miniport driver must follow these guidelines:

  • The PF miniport driver must verify that the VF, specified by the VFId member of the NDIS_SRIOV_WRITE_VF_CONFIG_SPACE_PARAMETERS structure, has resources that have been previously allocated. The PF miniport driver allocates resources for a VF through an OID method request of OID_NIC_SWITCH_ALLOCATE_VF.

    If resources for the specified VF have not been allocated, the driver must fail the OID request.

  • The PF miniport driver calls NdisMSetVirtualFunctionBusData to write to the requested PCI configuration space. However, the PF miniport driver can also return PCI configuration space data for the VF that the driver has cached from previous read or write operations of the PCI configuration space.

    Note  If an independent hardware vendor (IHV) provides a virtual bus driver (VBD) as part of its SR-IOV driver package, its PF miniport driver must not call NdisMSetVirtualFunctionBusData. Instead, the driver must interface with the VBD through a private communication channel, and request that the VBD call SetVirtualFunctionData. This function is exposed from the GUID_VPCI_INTERFACE_STANDARD interface that is supported by the underlying virtual PCI (VPCI) bus driver.

If the PF miniport driver can successfully complete the OID request, the driver must copy the requested PCI configuration space data to the buffer referenced by the InformationBuffer member of the NDIS_OID_REQUEST structure. The driver copies the data to the buffer at the offset specified by theBufferOffset member of the NDIS_SRIOV_READ_VF_CONFIG_SPACE_PARAMETERS structure.