OvmfPkg/Virtio: take RingBaseShift in SetQueueAddress()

For the case when an IOMMU is used for translating system physical
addresses to DMA bus master addresses, the transport-independent
virtio device drivers will be required to map their VRING areas to
bus addresses with VIRTIO_DEVICE_PROTOCOL.MapSharedBuffer() calls.

- MMIO and legacy virtio transport do not support IOMMU to translate the
  addresses hence RingBaseShift will always be set to zero.

- modern virtio transport supports IOMMU to translate the address, in
  next patch we will update the Virtio10Dxe to use RingBaseShift offset.

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
[lersek@redhat.com: remove commit msg paragraph with VirtioLib reference]
[lersek@redhat.com: fix typo in VIRTIO_SET_QUEUE_ADDRESS comment block]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/Include/Protocol/VirtioDevice.h

@@ -156,7 +156,21 @@ EFI_STATUS
   @param[in] This             This instance of VIRTIO_DEVICE_PROTOCOL
 
   @param[in] Ring             The initialized VRING object to take the
-                              addresses from.
+                              addresses from. The caller is responsible for
+                              ensuring that on input, all Ring->NumPages pages,
+                              starting at Ring->Base, have been successfully
+                              mapped with a single call to
+                              This->MapSharedBuffer() for CommonBuffer bus
+                              master operation.
+
+  @param[in] RingBaseShift    Adding this value using UINT64 arithmetic to the
+                              addresses found in Ring translates them from
+                              system memory to bus addresses. The caller shall
+                              calculate RingBaseShift as
+                              (DeviceAddress - (UINT64)(UINTN)HostAddress),
+                              where DeviceAddress and HostAddress (i.e.,
+                              Ring->Base) were output and input parameters of
+                              This->MapSharedBuffer(), respectively.
 
   @retval EFI_SUCCESS         The data was written successfully.
   @retval EFI_UNSUPPORTED     The underlying IO device doesn't support the
@@ -166,7 +180,8 @@ typedef
 EFI_STATUS
 (EFIAPI *VIRTIO_SET_QUEUE_ADDRESS) (
   IN VIRTIO_DEVICE_PROTOCOL  *This,
-  IN VRING                   *Ring
+  IN VRING                   *Ring,
+  IN UINT64                  RingBaseShift
   );
 
 /**