doc: add GVT-G porting guide

Transcode, review, and publish GVT-G porting guide documentation. Merged
glossary entries, added anchor links in GVT-g_api for referencing from
this document.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/api/GVT-g_api.rst

@@ -83,6 +83,7 @@ responses to user space modules, notified by vIRQ injections.
 .. kernel-doc:: include/linux/vhm/acrn_vhm_mm.h
    :functions: update_memmap_attr
 
+.. _MPT_interface:
 
 ACRN-GT mediated pass-through (MPT) interface
 **************************************************
@@ -143,6 +144,7 @@ This section describes the wrap functions:
                intel_gvt_hypervisor_unpause_domain
                intel_gvt_hypervisor_dom0_ready
 
+.. _intel_gvt_ops_interface:
 
 GVT-g intel_gvt_ops interface
 *****************************
@@ -183,6 +185,8 @@ in the `ACRN kernel GitHub repo`_
                intel_gvt_activate_vgpu
                intel_gvt_deactivate_vgpu
 
+.. _sysfs_interface:
+
 ACRN-GT sysfs interface
 ***********************
 

doc/developer-guides/GVT-G-porting.rst

@@ -0,0 +1,174 @@
+.. _GVT-G-porting:
+
+GVT-G Enabling and Porting Guide
+################################
+
+Introduction
+************
+
+GVT-g is Intel's Open Source GPU virtualization solution, up-streamed to
+the Linux kernel. Its implementation over KVM is named KVMGT, over Xen
+is named XenGT, and over ACRN is named ACRN-GT. GVT-g can export
+multiple virtual-GPU (vGPU) instances for virtual machine (VM) system. A
+VM can be assigned one instance of a vGPU. The guest OS graphic driver
+needs only minor modifications to drive the vGPU adapter in a VM. Every
+vGPU instance adopts the full HW GPU's acceleration capability for
+media, 3D renderingi, and display.
+
+ACRN-GT refers to the glue layer between the ACRN hypervisor and GVT-g
+core device model. It works as the agent of hypervisor-related services.
+It is the only layer that needs to be rewritten when porting GVT-g to
+other specific hypervisors.
+
+For simplicity, in the rest of this document, the term GVT is used to
+refer to the core device model component of GVT-g, specifically
+corresponding to ``gvt.ko`` when build as a module.
+
+Purpose of this document
+************************
+
+This document explains the relationship between components of GVT-g in
+the ACRN hypervisor, shows how to enable GVT-g on ACRN, and guides
+developers  porting GVT-g to work on other hypervisors.
+
+This document describes:
+
+-  the overall components of GVT-g
+-  interaction interface of each components
+-  core interaction scenarios
+
+APIs of each component interface can be found in the :ref:`GVT-g_api`
+documentation.
+
+
+Overall Components
+******************
+
+For the GVT-g solution for the ACRN  hypervisor, there are two
+key modules: ACRN-GT and GVT:
+
+ACRN-GT module
+  Compiled from ``drivers/gpu/drm/i915/gvt/acrn_gvt.c``, the ACRN-GT
+  module acts as a glue layer between the ACRN hypervisor and the
+  interface to the ACRN-DM in user space.
+
+  ACRN-GT is the agent of hypervisor related services, including I/O trap
+  request, IRQ injection, address translation, VM controls, etc. It also
+  listens to ACRN hypervisor in ``acrngt_emulation_thread``, and informs GVT
+  module of I/O traps.
+
+  It calls into the GVT module's :ref:`intel_gvt_ops_interface` to invoke
+  Device Model's routines, and receives request from GVT module through
+  the :ref:`MPT_interface`.
+
+  User space programs, such as ACRN-DM, communicate with ACRN-GT through
+  the :ref:`sysfs_interface` by writing to sysfs node
+  ``/sys/kernel/gvt/control/create_gvt_instance``.
+
+  This is the only module that needs to be rewritten when porting to
+  another embedded device hypervisor.
+
+GVT module
+  This Device Model service is the central part of all
+  GVT-g components. It receives workloads from each vGPU, shadows the
+  workloads, and dispatches the workloads to Dom0's i915 module to deliver
+  workloads to real hardware. It also emulates the virtual display to each
+  VM.
+
+VHM module
+  This is a kernel module that requires an interrupt (vIRQ) number,
+  and exposes APIs to external kernel modules such as GVT-g, and the
+  virtIO BE service running in kernel space. It exposes a char device node
+  in user space, and only interacts with the DM. The DM routes I/O
+  requests and responses between other modules to and from the VHM module
+  via the char device. DM may use the VHM for hypervisor service
+  (including remote memory map), and VHM may directly service the request
+  such as for the remote memory map, or invoking hypercall. It also sends
+  I/O responses to user space modules, notified by vIRQ injections.
+
+
+.. figure:: images/GVT-G-porting-image1.png
+   :width: 700px
+   :align: center
+   :name: GVT-g_components
+
+   GVT-g components and interfaces
+
+Core scenario interaction sequences
+***********************************
+
+
+vGPU creation scenario
+======================
+
+In this scenario, ACRN-GT receives a create request from ACRN-DM. It
+calls GVT's :ref:`intel_gvt_ops_interface` to inform GVT of vGPU
+creation. This interface sets up all vGPU resources such as MMIO, GMA,
+PVINFO, GTT, DISPLAY, and Execlists, and calls back to the ACRN-GT
+module through the :ref:`MPT_interface` ``attach_vgpu``. Then, the
+ACRN-GT module sets up an I/O request server and asks to trap the PCI
+configure space of the vGPU (virtual device 0:2:0) via VHM's APIs.
+Finally, the ACRN-GT module launches a ACRN-GT emulation thread to
+listen to I/O trap notifications from HVM and ACRN hypervisor.
+
+vGPU destroy scenario
+=====================
+
+In this scenario, ACRN-GT receives a destroy request from ACRN-DM. It
+calls GVT's :ref:`intel_gvt_ops_interface` to inform GVT of the vGPU destroy
+request, and cleans up all vGPU resources.
+
+vGPU pci configure space write scenario
+=======================================
+
+ACRN traps the vGPU's PCI config space write, notifies ACRN-GT's
+``acrngt_emulation_thread``, which calls ``acrngt_hvm_pio_emulation`` to
+handle all I/O trap notifications. This routine calls the GVT's
+:ref:`intel_gvt_ops_interface` ``emulate_cfg_write`` to emulate the vGPU PCI
+config space write:
+
+#. If it's BAR0 (GTTMMIO) write, turn on/off GTTMMIO trap, according to
+   the write value.
+#. If it's BAR1 (Aperture) write, maps/unmaps vGPU's aperture to its
+   corresponding part in the host's aperture.
+#. Otherwise, write to the virtual PCI configuration space of the vGPU.
+
+pci configure space read scenario
+=================================
+
+Call sequence is almost the same as the write scenario above,
+but instead it calls the GVT's :ref:`intel_gvt_ops_interface`
+``emulate_cfg_read`` to emulate the vGPU PCI config space read.
+
+GGTT read/write scenario
+========================
+
+GGTT's trap is set up in the pci configure space write
+scenario above.
+
+MMIO read/write scenario
+========================
+
+MMIO's trap is set up in the pci configure space write
+scenario above.
+
+PPGTT write protection page set/unset scenario
+==============================================
+
+PPGTT write protection page is set by calling ``acrn_ioreq_add_iorange``
+with range type as ``REQ_WP``, and trap its write to device model while
+allowing read without trap.
+
+PPGTT write protection page is unset by calling ``acrn_ioreq_del_range``.
+
+PPGTT write protection page write
+=================================
+
+In the VHM module, ioreq for PPGTT WP and MMIO trap is the same. It will
+also be trapped into the routine ``intel_vgpu_emulate_mmio_write()``.
+
+API details
+***********
+
+APIs of each component interface can be found in the :ref:`GVT-g_api`
+documentation.

doc/developer-guides/index.rst

@@ -24,6 +24,7 @@ specific areas within the ACRN hypervisor system.
    ACPI-virt-hld.rst
    APL_GVT-g-hld.rst
    uart-virtualization.rst
+   GVT-G-porting.rst
 
 Contributing to the project
 ***************************

doc/glossary.rst

@@ -20,7 +20,7 @@ Glossary of Terms
       A user mode device model application running in Service OS to provide
       device emulations in ACRN hypervisor.
 
-   aperture
+   aperture, Low GM
       CPU-visible graphics memory
 
    API
@@ -36,6 +36,9 @@ Glossary of Terms
    BIOS
       Basic Input/Output System.
 
+   Dom0 i915
+      The Intel Graphics driver running in Domain 0
+
    ELSP
       GPU's ExecList submission port
 
@@ -71,6 +74,9 @@ Glossary of Terms
    GVT-s
       Virtual shared graphics acceleration (multiple VMs to one physical GPU)
 
+   Hidden GM, High GM
+      Hidden or High graphics memory, not visible to the CPU.
+
    I2C
       Inter-Integrated Circuit