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The SR-IOV virtualization document Tracked-On: #4433 Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
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307 lines
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.. _sriov_virtualization:
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SR-IOV Virtualization
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=====================
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SR-IOV (Single Root Input/Output Virtualization) can isolate PCIe devices
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and make the devices to have good performance, close to bare-metal. The
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SR-IOV consists of two basic units, one is called PF(Physical Function)
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that supports SR-IOV PCIe extended capability and manages entire
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physical device, another is called VF (Virtual Function) and is a
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"lightweight" PCIe function which is meant to be given to a VM as a
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pass-through device.
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For more details, please refer to PCI Express Base Specification Revision 4.0,
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Version 1.0 `PCI-SIG Specification <https://pcisig.com/specifications>` Chapter 9.
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SR-IOV Architectural Overview
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-----------------------------
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.. figure:: images/sriov-image1.png
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:align: center
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:width: 900px
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:name: SR-IOV-architecture-overview
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SR-IOV Architectural Overview
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- **SI** - System Image known as a VM.
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- **VI** - Virtualization Intermediary known as Hypervisor.
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- **SR-PCIM** - Single Root PCI Manager is a software entity for SR-IOV
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management.
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- **PF** - A PF is a PCIe Function that supports the SR-IOV capability
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and is accessible to an SR-PCIM, a VI, or an SI.
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- **VF** - A VF is a “light-weight” PCIe Function that is directly
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accessible by an SI.
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SR-IOV Extended Capability
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--------------------------
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The SR-IOV Extended Capability defined here is a PCIe extended
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capability that must be implemented in each PF device that supports
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SR-IOV feature. This Capability is used to describe and control a PF’s
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SR-IOV Capabilities.
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.. figure:: images/sriov-image2.png
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:align: center
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:width: 900px
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:name: SR-IOV-extended-capability
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SR-IOV Extended Capability
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- **PCIe Extended Capability ID** - 0010h.
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- **SR-IOV Capabilities** - VF Migration Capable and ARI Capable.
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- **SR-IOV Control** - Enable/Disable VFs, VF migration state query.
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- **SR-IOV Status** - VF Migration Status
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- **InitialVFs** - Indicates to SR-PCIM the number of VFs that are
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initially associated with the PF
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- **TotalVFs** - Indicates the maximum number of VFs that could be
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associated with the PF
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- **NumVFs** - Controls the number of VFs that are visible. *NumVFs* <=
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*InitialVFs* = *TotalVFs*.
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- **Function Link Dependency** - The field is used to describe these
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dependencies between PFs. VF dependencies are the same as the
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dependencies of their associated PFs.
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- **First VF Offset** - It is a constant and defines the Routing ID
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offset of the first VF that is associated with the PF that contains
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this Capability structure
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- **VF Stride** - It defines the Routing ID offset from one VF to the
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next one for all VFs associated with the PF that contains this
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Capability structure.
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- **VF Device ID** - This field contains the Device ID that should be
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presented for every VF to the SI.
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- **Supported Page Sizes** - This field indicates the page sizes
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supported by the PF.
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- **System Page Size** - This field defines the page size the system
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will use to map the VFs’ memory addresses. Software must set the
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value of the *System Page Size* to one of the page sizes set in the
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*Supported Page Sizes* field
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- **VF BARs** - These fields must define the VF’s Base Address
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Registers (BARs). These fields behave as normal PCI BARs.
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- **VF Migration State Array Offset** - This register shall contain a
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PF BAR relative pointer to the VF Migration State Array.
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- **VF Migration State Array** – It is located using the VF Migration
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State Array Offset register of the SR-IOV Capability block.
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For more details, please refer to *PCI Express Base Specification
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Revision 4.0, Version 1.0 Chapter 9.3.3*
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SR-IOV Architecture In ACRN
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---------------------------
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.. figure:: images/sriov-image3.png
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:align: center
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:width: 900px
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:name: SR-IOV-architecure-in-acrn
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SR-IOV Architectural in ACRN
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1. Hypervisor detects SR-IOV capable PCIe device in physical PCI device
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enumeration phase.
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2. Hypervisor intercepts the PF’s SR-IOV capability accessing to
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enable/disable VF devices based on *VF\_ENABLE* state, and all
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read/write requests for PF device are passthrough to PF physical
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device.
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3. Hypervisor waits for 100ms after *VF\_ENABLE* is set and initialize
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VF devices. The differences between normal passthrough device and
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SR-IOV VF device are physical device detection, BARs and MSIx
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initializations. Hypervisor uses *Subsystem Vendor ID* to detect
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SR-IOV VF physical device instead *Vendor ID* since there is no valid
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*Vendor ID* for SR-IOV VF physical device, the VF BARs are
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initialized by its associated PF’s SR-IOV capabilities not PCI
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standard BAR registers, MSIx mapping base address is also from PF’s
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SR-IOV capabilities not PCI standard BAR registers.
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SR-IOV Passthrough VF Architecture In ACRN
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------------------------------------------
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.. figure:: images/sriov-image4.png
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:align: center
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:width: 900px
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:name: SR-IOV-vf-passthrough
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SR-IOV VF Passthrough Architecture In ACRN
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1. The SR-IOV VF device needs to bind PCI-stud driver instead
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vendor-specific VF driver before passthrough the device.
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2. User configures ``acrn-dm`` boot parameter with passthrough SR-IOV VF
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device. When User VM starts, ``acrn-dm`` invokes a hypercall to set the
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*vdev-VF0* device in User VM.
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3. Hypervisor emulates *Device ID/Vendor ID* and *Memory Space Enable
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(MSE*) in configuration space for an assigned SR-IOV VF device. The
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assigned VF *Device ID* comes from its associated PF’s capability,
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*Vendor ID* is same with PF’s *Vendor ID* and *MSE* is always set
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when reading the SR-IOV VF device *CONTROL* register
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4. Vendor-specific VF driver in target VM probes the assigned SR-IOV VF
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device.
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SR-IOV Initialization Flow
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--------------------------
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.. figure:: images/sriov-image5.png
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:align: center
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:width: 900px
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:name: SR-IOV-init-flow
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SR-IOV Initialization Flow
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When a SR-IOV capable device is initialized, all access to the
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configuration space will pass through to the physical device directly.
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Service VM can identify all capabilities of the device from SR-IOV extended
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capability then create sysfs node for SR-IOV management.
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SR-IOV VF Enable Flow
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---------------------
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.. figure:: images/sriov-image6.png
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:align: center
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:width: 900px
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:name: SR-IOV-enable-flow
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SR-IOV VF Enable Flow
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Application enables n VF devices via a SR-IOV PF device *sysfs* node.
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Hypervisor intercepts all SR-IOV capability accesses and check
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*VF\_ENABLE* state, if the *VF\_ENABLE* is set, hypervisor creates n
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virtual devices after 100ms that VF physical devices have enough time to
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be created. Service VM waits 100ms then only accesses the first VF device’s
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configuration space including *Class Code, Reversion ID, Subsystem
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Vendor ID, Subsystem ID,* Service VM uses the first VF device information to
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initialize subsequent VF devices.
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SR-IOV VF Disable Flow
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----------------------
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.. figure:: images/sriov-image7.png
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:align: center
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:width: 900px
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:name: SR-IOV-disable-flow
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SR-IOV VF Disable Flow
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Application disables SR-IOV VF devices by writing zero to SR-IOV PF
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device *sysfs* node. Hypervisor intercepts all SR-IOV capability
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accesses and check *VF\_ENABLE* state, if *VF\_ENABLE* is clear,
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hypervisor makes VF virtual devices invisible from Service VM that all accesses
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for VF will return 0xFFFFFFFF as an error, VF physical devices are
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removed within 1s of *VF\_ENABLE* is clear.
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SR-IOV VF Assignment Policy
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---------------------------
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.. figure:: images/sriov-image8.png
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:align: center
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:width: 900px
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:name: SR-IOV-vf-assignment
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SR-IOV VF Assignment
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1. All SR-IOV PF devices are managed by Service VM.
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2. Currently, SR-IOV PF can’t passthrough to User VM.
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3. All VFs can be passthrough to User VM, but we do not recommend
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passthrough to high privilege VMs, because PF device may impact
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assigned VFs including functionality and stability.
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SR-IOV Usage Guide In ACRN
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--------------------------
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We use Intel 82576 NIC as an example in here and only support LaaG
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(Linux as a Guest).
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1. Please ensure the 82576 VF driver is compiled into User VM Kernel
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(Set *CONFIG\_IGBVF=y* in Kernel Config).
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2. When the Service VM boot up, “\ *lspci -v*\ ” command can show Intel 82576
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NIC devices have SR-IOV capability and their PF drivers are ``igb``.
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.. figure:: images/sriov-image9.png
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:align: center
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:width: 900px
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:name: 82576-pf
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82576 SR-IOV PF devices
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1. Input "\ *echo n > /sys/class/net/enp109s0f0/device/sriov\_numvfs*\ "
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command in Service VM to enable n VF devices for the first PF
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device(\ *enp109s0f0)*. The number *n* can’t more than *TotalVFs*
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that comes from the return value of command
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*“cat /sys/class/net/enp109s0f0/device/sriov\_totalvfs”*. Here we use
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*n = 2* for the example.
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.. figure:: images/sriov-image10.png
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:align: center
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:width: 900px
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:name: 82576-vf
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82576 SR-IOV VF devices
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.. figure:: images/sriov-image11.png
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:align: center
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:width: 900px
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:name: 82576-vf-nic
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82576 SR-IOV VF NIC
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1. Passthrough a SR-IOV VF device to guest
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a. Unbind igbvf driver in Service VM
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i. *modprobe pci\_stub*
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ii. *echo "8086 10ca" > /sys/bus/pci/drivers/pci-stub/new\_id*
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iii. *echo "0000:6d:10.0" >
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/sys/bus/pci/devices/0000:6d:10.0/driver/unbind*
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iv. *echo "0000:6d:10.0" >
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/sys/bus/pci/drivers/pci-stub/bind*
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b. Add SR-IOV VF device parameter (“*-s X, passthru,6d/10/0*\ ”) in
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launch User VM script
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.. figure:: images/sriov-image12.png
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:align: center
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:width: 900px
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:name: 82576-nic-passthru
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Configure 82576 NIC as Passthrough Device
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a. Boot User VM
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SR-IOV Limitations In ACRN
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--------------------------
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1. The SR-IOV migration feature is not supported.
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2. If one SR-IOV PF device is detected during enumeration phase, but there is no
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enough room for its total VF devices, the PF device will be dropped. The platform
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uses *MAX_PCI_DEV_NUM* ACRN configuration to support the maximum number of PCI
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devices, please make sure *MAX_PCI_DEV_NUM* is more than the number of all PCI
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devices including total SR-IOV VF devices.
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