Frequently Asked Questions¶

Here are some frequently asked questions about the ACRN project.

What hardware does ACRN support?
How do I configure ACRN’s memory size?
How to modify the default display output for a User VM?
Why does ACRN need to know how much RAM the system has?

What hardware does ACRN support?¶

ACRN runs on Intel boards, as documented in our Supported Hardware documentation.

How do I configure ACRN’s memory size?¶

It’s important that the ACRN Kconfig settings are aligned with the physical memory on your platform. Check the documentation for these option settings for details:

For example, if the Intel NUC’s physical memory size is 32G, you may follow these steps to make the new UEFI ACRN hypervisor, and then deploy it onto the Intel NUC to boot the ACRN Service VM with the 32G memory size.

Use make menuconfig to change the RAM_SIZE:

$ cd acrn-hypervisor
$ make menuconfig -C hypervisor BOARD=nuc7i7dnb

Navigate to these items and then change the value as given below:

(0x0f000000) Size of the RAM region used by the hypervisor
(0x800000000) Size of the physical platform RAM
(0x800000000) Size of the Service OS (SOS) RAM

Press S and then Enter to save the .config to the default directory: acrn-hypervisor/hypervisor/build/.config
Press ESC to leave the menu.
Then continue building the ACRN Service VM as usual.

How to modify the default display output for a User VM?¶

Apollo Lake HW has three pipes and each pipe can have three or four planes which help to display the overlay video. The hardware can support up to 3 monitors simultaneously. Some parameters are available to control how display monitors are assigned between the Service VM and User VM(s), simplifying the assignment policy and providing configuration flexibility for the pipes and planes for various IoT scenarios. This is known as the plane restriction feature.

i915.avail_planes_per_pipe: for controlling how planes are assigned to the pipes
i915.domain_plane_owners: for controlling which domain (VM) will have access to which plane

Refer to GVT-g (AcrnGT) Kernel Options details for detailed parameter descriptions.

In the default configuration, pipe A is assigned to the Service VM and pipes B and C are assigned to the User VM, as described by these parameters:

Service VM:

i915.avail_planes_per_pipe=0x01010F
i915.domain_plane_owners=0x011111110000

User VM:
```
i915.avail_planes_per_pipe=0x0070F00
```

To assign pipes A and B to the User VM, while pipe C is assigned to the Service VM, use these parameters:

Service VM:

i915.avail_planes_per_pipe=0x070101
i915.domain_plane_owners=0x000011111111

User VM:
```
i915.avail_planes_per_pipe=0x000F0F
```

Note

The Service VM always has at least one plane per pipe. This is intentional, and the driver will enforce this if the parameters do not do this.

Why does ACRN need to know how much RAM the system has?¶

Configuring ACRN at compile time with the system RAM size is a tradeoff between flexibility and functional safety certification. For server virtualization, one binary is typically used for all platforms with flexible configuration options given at run time. But, for IoT applications, the image is typically configured and built for a particular product platform and optimized for that product.

Important features for ACRN include Functional Safety (FuSa) and real-time behavior. FuSa requires a static allocation policy to avoid the potential of dynamic allocation failures. Real-time applications similarly benefit from static memory allocation. This is why ACRN removed all malloc()-type code, and why it needs to pre-identify the size of all buffers and structures used in the Virtual Memory Manager. For this reason, knowing the available RAM size at compile time is necessary to statically allocate memory usage.