docs: Add documentation for SR-IOV and Virtualization Enhancements

Documentation describes 5 new parameters being added regarding SR-IOV:
sriov_max_vfs
sriov_vq_flexible
sriov_vi_flexible
sriov_max_vi_per_vf
sriov_max_vq_per_vf

The description also includes the simplest possible QEMU invocation
and the series of NVMe commands required to enable SR-IOV support.

Signed-off-by: Lukasz Maniak <lukasz.maniak@linux.intel.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>

docs/system/devices/nvme.rst

@@ -239,3 +239,85 @@ The virtual namespace device supports DIF- and DIX-based protection information
   to ``1`` to transfer protection information as the first eight bytes of
   metadata. Otherwise, the protection information is transferred as the last
   eight bytes.
+
+Virtualization Enhancements and SR-IOV (Experimental Support)
+-------------------------------------------------------------
+
+The ``nvme`` device supports Single Root I/O Virtualization and Sharing
+along with Virtualization Enhancements. The controller has to be linked to
+an NVM Subsystem device (``nvme-subsys``) for use with SR-IOV.
+
+A number of parameters are present (**please note, that they may be
+subject to change**):
+
+``sriov_max_vfs`` (default: ``0``)
+  Indicates the maximum number of PCIe virtual functions supported
+  by the controller. Specifying a non-zero value enables reporting of both
+  SR-IOV and ARI (Alternative Routing-ID Interpretation) capabilities
+  by the NVMe device. Virtual function controllers will not report SR-IOV.
+
+``sriov_vq_flexible``
+  Indicates the total number of flexible queue resources assignable to all
+  the secondary controllers. Implicitly sets the number of primary
+  controller's private resources to ``(max_ioqpairs - sriov_vq_flexible)``.
+
+``sriov_vi_flexible``
+  Indicates the total number of flexible interrupt resources assignable to
+  all the secondary controllers. Implicitly sets the number of primary
+  controller's private resources to ``(msix_qsize - sriov_vi_flexible)``.
+
+``sriov_max_vi_per_vf`` (default: ``0``)
+  Indicates the maximum number of virtual interrupt resources assignable
+  to a secondary controller. The default ``0`` resolves to
+  ``(sriov_vi_flexible / sriov_max_vfs)``
+
+``sriov_max_vq_per_vf`` (default: ``0``)
+  Indicates the maximum number of virtual queue resources assignable to
+  a secondary controller. The default ``0`` resolves to
+  ``(sriov_vq_flexible / sriov_max_vfs)``
+
+The simplest possible invocation enables the capability to set up one VF
+controller and assign an admin queue, an IO queue, and a MSI-X interrupt.
+
+.. code-block:: console
+
+   -device nvme-subsys,id=subsys0
+   -device nvme,serial=deadbeef,subsys=subsys0,sriov_max_vfs=1,
+    sriov_vq_flexible=2,sriov_vi_flexible=1
+
+The minimum steps required to configure a functional NVMe secondary
+controller are:
+
+  * unbind flexible resources from the primary controller
+
+.. code-block:: console
+
+   nvme virt-mgmt /dev/nvme0 -c 0 -r 1 -a 1 -n 0
+   nvme virt-mgmt /dev/nvme0 -c 0 -r 0 -a 1 -n 0
+
+  * perform a Function Level Reset on the primary controller to actually
+    release the resources
+
+.. code-block:: console
+
+   echo 1 > /sys/bus/pci/devices/0000:01:00.0/reset
+
+  * enable VF
+
+.. code-block:: console
+
+   echo 1 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
+
+  * assign the flexible resources to the VF and set it ONLINE
+
+.. code-block:: console
+
+   nvme virt-mgmt /dev/nvme0 -c 1 -r 1 -a 8 -n 1
+   nvme virt-mgmt /dev/nvme0 -c 1 -r 0 -a 8 -n 2
+   nvme virt-mgmt /dev/nvme0 -c 1 -r 0 -a 9 -n 0
+
+  * bind the NVMe driver to the VF
+
+.. code-block:: console
+
+   echo 0000:01:00.1 > /sys/bus/pci/drivers/nvme/bind