Hafnium RAM disk

Hafnium expects to find the following files in the root directory of its RAM disk:

• vmlinuz -- the kernel of the primary VM.
• initrd.img -- the initial ramdisk of the primary VM.
• manifest.dtb -- hypervisor configuration file.
• kernels for the secondary VMs, whose names are described in the manifest.

Follow the preparing Linux instructions to produce vmlinuz and initrd.img for a basic Linux primary VM.

Manifest file

The format is currently a simple Device Tree:

/dts-v1/;

/ {
	hypervisor {
		vm1 {
			debug_name = "name";
		};

		vm2 {
			debug_name = "name";
			kernel_filename = "filename";
			vcpu_count = <N>;
			mem_size = <M>;
		};
		...
	};
};

For example, the following defines two secondary VMs, the first one with 1MB of memory, 2 CPUs and kernel image called kernel0, while the second one has 2MB of memory, 4 CPUs and a kernel image called kernel1.

/dts-v1/;

/ {
	hypervisor {
		vm1 {
			debug_name = "primary VM";
		};

		vm2 {
			debug_name = "secondary VM 1";
			kernel_filename = "kernel0";
			vcpu_count = <2>;
			mem_size = <0x100000>;
		};

		vm3 {
			debug_name = "secondary VM 2";
			kernel_filename = "kernel1";
			vcpu_count = <4>;
			mem_size = <0x200000>;
		};
	};
};

Hafnium expects the manifest in Device Tree Blob format. Compile it with:

dtc -I dts -O dtb --out-version 17 -o manifest.dtb <manifest_source_file>

Create a RAM disk for Hafnium

Assuming that a subdirectory called initrd contains the files listed in the previous section, we can build initrd.img with the following command:

cd initrd; find . | cpio -o > ../initrd.img; cd -