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Querying the PCI Configuration Space for a Virtual Function

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Note This method can only be used by overlying drivers that run in the management operating system of the Hyper-V parent partition.

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 PCIe configuration space. Only the miniport driver for the PCIe Physical Function (PF) can access the PCIe 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.

An overlying driver that runs in the management operating system issues an object identifier (OID) method request of OID_SRIOV_READ_VF_CONFIG_SPACE to read data from the PCIe configuration space for a specified VF on the network adapter.

For example, the virtualization stack that runs in the management operating system issues the OID method request of OID_SRIOV_READ_VF_CONFIG_SPACE when the VF miniport driver calls NdisMGetBusData to read from its VF PCIe configuration space.

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

  • The VFId member must be set to the identifier of the VF from which the information is to be read.

  • The Offset member must be set to the offset within the PCIe configuration space of the VF in which data will be read.

  • The Length member must be set to the number of bytes to read from the VF's PCIe configuration space.

  • The BufferOffset member must be set to the offset within the buffer (referenced by the InformationBuffer member) that will contain the data that is read from the specified VF's PCI configuration space. This offset is specified in units of bytes from the beginning of the NDIS_SRIOV_READ_VF_CONFIG_SPACE_PARAMETERS structure.

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

  • The miniport driver must verify that the VF, specified by the VFId member of the NDIS_SRIOV_READ_VF_CONFIG_SPACE_PARAMETERS structure, has resources that have been previously allocated. The 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 miniport driver must verify that the buffer (referenced by the InformationBuffer member of the NDIS_OID_REQUEST structure) is large enough to return the requested PCIe configuration space data. If this is not true, the driver must fail the OID request.

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

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

After a successful return from this OID method request, the InformationBuffer member of the NDIS_OID_REQUEST structure contains a pointer to a caller-allocated buffer. This buffer is formatted to contain the following: