1.
ACRN GVT-d Introduction and Tutorial
ZHAO Yakui
Zhao Yakui <Yakui.zhao@intel.com>
05/20/2020

2.
Agenda
● Background
● Design of GVT-d
● How to use GVT-d

3.
Background

4.
GPU Virtualization Approaches
API Forwarding Mediated Pass-thru Direct Pass-thru
Low perf
Compatibility issue
Currently used in ACRN
Named GVT-g
Pass-thru GPU
Named GVT-d

5.
Why chose GVT-d
• Support GVT-d is simpler than GVT-g for industrial scenario as only
one VM require graphic support
• GVT-d has better performance than GVT-g

6.
Design of GVT-d

7.
GVT-d initialization flow
• Register PCI device in ACRN DM
• Add one PCI device from the passthru PCI device
• Add the pci_config_read/write callback
• Initialize the PCI caps for guest system
• Construct the PCI bar for Guest OS
• Allocate/initialize the PCI bar for guest OS
• construct the EPT mapping from the guest PCI bar to host PCI mmio_addr
• This will allow the guest OS to read/write the PCI mmio_registers without Vm-exit
• Let hypervisor to prepare DMAR addr translation for passthru-device
• Use vm_assign_ptdev SOS_ioctl to communicate with the hypervisor
• DMAR addr translation logic allows the pass-thru device to read/write the system
memory in Guest by using DMA
• This is based on VT-d IOMMU
• https://projectacrn.github.io/latest/developer-guides/hld/hv-vt-d.html

8.
Extra resources required by GVT-d
Pass-thru Graphics stolen memory
• Allow Guest VM to reuse the framebuffer memory allocated by native BIOS
Pass-thru OpRegion
• Describe board GPU specific information
• For example: HDMI/DP ports, eDP timing info
• Guest graphic driver relies on it to communicate with native BIOS during GPU
initialization
Create dummy LPC bridge
• Windows guest graphics driver need a LPC bridge located on bdf 00:1f.0 to
initialize the platform-specific info

9.
How to use GVT-d

10.
BIOS setting on WHL platforms
• Set 64MB graphics stolen memory

11.
BIOS setting on WHL platforms(2)
• Set 64MB graphics stolen memory
• Set enabled for PM support

12.
GVT-d usage example
echo "8086 $GPU_DEVICE_ID" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:02.0" > /sys/bus/pci/devices/0000:00:02.0/driver/unbind
echo "0000:00:02.0" > /sys/bus/pci/drivers/pci-stub/bind
acrn-dm -A -m $mem_size -s 0:0,hostbridge
…
-s 2,passthru,0/2/0,gpu
…
1. Load the pci_stub driver for the Intel GPU device
2. Pass-thru Intel GPU device for ACRN DM

13.
Q&A