ACRN Project Technical Community Meeting Minutes - 1/23/2019

Wang, Hongbo

ACRN Project TCM - 23th January 2019
  1. ACRN project update
  1. LIU, Xinyun:  HyperDMA Sharing between
Download foil from ACRN Presentation->ACRN_TCM->WW04’19
Q1: What's the pros and cons of the two display model?
A: In general, direct display model is based display H/W resource isolation. Indirect display model is based on memory sharing across virtual machine.
Plane Restriction (Direct Display Mode) Hyper DMABUF ( Indirect display Mode)
display H/W isolation Cons:
UOS needs to occupy some plane of the pipe which assigned to SOS.
UOS don't needs to occupy some plane of the pipe which assigned to SOS.
display H/W sharing Cons:
Complicated to implement dynamic plane resource management for  Plane restriction feature and no plan yet
SOS utilize the whole pipe resource and no need to implement this feature.
User App  development Cons:
Complicated for user to develop Apps to control output in H/W plane level;
Not always applicable for user to use the plane as the extended monitor;
For display purpose only;
Easy use API to reexport/import dma-buf as local buffer
Can expanded to other domain besides for display
Security Pros:
SOS doesn't know the content from UOS
SOS use the content from UOS as a local buffer
performance Pros:
UOS do flip as 'directly' to the display engine.
Latency introduced due to communication between VM and do synchronization of buffer lifecycle management
Q2: For hyperDMA sharing, is it one way direction sharing or bi-direction?
A: Hyper DMABUF sharing  is designed to support bi-direction sharing. But it depends on hypervisor capability. For ACRN, it allows share dma-buf generated in UOS to SOS only. The hyper DMABUF sharing can’t work between guest VMs or  SOS to UOS, because UOS can only access physical memory address assigned to itself in ACRN.
Q3: Can DMA buff be shared with other VMs, 1:1 mapping? Can we do N:1 mapping?
A: In ACRN, it supports multiple UOSs to sharing DMABUF to SOS. Hyper dmabuf ID is designed to contain the VM’s ID, so We can do correct page address extraction and conversion
Q4: How to end the DMAbuff sharing?
A: hyper dmabuf device provides  ioctl() of IOCTL_HYPER_DMABUF_UNEXPORT to stop Hyper DMABUF sharing explicitly from Exporter side.  The close() also stop sharing implicitly.
  1. All: Community open discussion.
  1. Next meeting agenda proposal:
WW Topic Presenter Status
WW02 TPM2.0 virtualization in ACRN DENG, Wei 1/9
WW03 Polling mode Virtio and its advantage for RT VM DENG, Jie Today
WW04 Buffer sharing from UOS to SOS, HyperDMA usage LIU, Xinyun Plan
  1. TBD
  1. Project URL:
  1. Portal:   
  2. Source code:   
  3. email: info@...g
  4. Technical Mailing list: acrn-dev@...g
  1. Recommended Hardware platform (reference):
  1. Apollo Lake (SoC) UP2 (with serial port): AAEON UPS-APLC2-A10-0232
  2. Apollo Lake (SoC) NUC (without serial port): NUC6CAYHL (at least 8G memory)
  3. Kabylake (Core) NUC (with serial port): NUC7i5BNH
Best regards.
Tel: +86-21-6116 7445
MP: +86-1364 1793 689