Custom Kernels in krata

Krata supports using custom kernels instead of the default Edera-provided kernel both on a system-wide and zone-wide basis. Krata also supports using a custom host kernel, as long as it meets certain technical requirements.

System-wide default kernel for zones

The standard system-wide default kernel for zones is stored in /var/lib/krata/zone/kernel which is the kernel image that should be booted for the zone, and /var/lib/krata/zone/addons.squashfs, which contains a set of kernel modules that should be mounted in the zone.

Zone-wide alternative kernels via OCI

Krata also supports fetching alternative kernel images for use in zones via OCI repositories. These kernel images are distributed like any other OCI image, but are not intended to be directly executed by an OCI runtime.

To select an alternative kernel, you can supply the -k option to the kratactl zone launch command that specifies an OCI tag to pull the alternative kernel image from.

OCI-based kernel image contents

OCI-based kernel images contain the following files:

/kernel/image: The kernel image itself.
/kernel/addons.squashfs: A squashfs file containing the kernel modules for a given kernel image.
/kernel/metadata: A file containing the following metadata fields in KEY=VALUE format:
- KERNEL_ARCH: The kernel architecture (x86_64 or aarch64)
- KERNEL_VERSION: The kernel version
- KERNEL_FLAVOR: The kernel flavor (examples: standard, dom0 or openpax)
- KERNEL_CONFIG: The digest for the relevant configuration file stored in the OCI repository
- KERNEL_TAGS: The OCI tags this kernel image was originally built for (example: latest)

Minimum requirements for a zone-wide/system-wide kernel

The following configuration options must be set:

CONFIG_XEN=y
CONFIG_XEN_PV=y
CONFIG_XEN_512GB=y
CONFIG_XEN_PV_SMP=y
CONFIG_XEN_PVHVM=y
CONFIG_XEN_PVHVM_SMP=y
CONFIG_XEN_PVHVM_GUEST=y
CONFIG_XEN_SAVE_RESTORE=y
CONFIG_XEN_PVH=y
CONFIG_XEN_PV_MSR_SAFE=y
CONFIG_PCI_XEN=y
CONFIG_NET_9P_XEN=y
CONFIG_XEN_PCIDEV_FRONTEND=y
CONFIG_XEN_BLKDEV_FRONTEND=y
CONFIG_XEN_NETDEV_FRONTEND=y
CONFIG_INPUT_XEN_KBDDEV_FRONTEND=y
CONFIG_HVC_XEN=y
CONFIG_HVC_XEN_FRONTEND=y
CONFIG_XEN_FBDEV_FRONTEND=m
CONFIG_XEN_BALLOON=y
CONFIG_XEN_BALLOON_MEMORY_HOTPLUG=y
CONFIG_XEN_MEMORY_HOTPLUG_LIMIT=512
CONFIG_XEN_SCRUB_PAGES_DEFAULT=y
CONFIG_XEN_DEV_EVTCHN=y
CONFIG_XEN_BACKEND=y
CONFIG_XENFS=y
CONFIG_XEN_COMPAT_XENFS=y
CONFIG_XEN_SYS_HYPERVISOR=y
CONFIG_XEN_XENBUS_FRONTEND=y
CONFIG_SWIOTLB_XEN=y
CONFIG_XEN_HAVE_PVMMU=y
CONFIG_XEN_EFI=y
CONFIG_XEN_AUTO_XLATE=y
CONFIG_XEN_ACPI=y
CONFIG_XEN_HAVE_VPMU=y
CONFIG_XEN_GRANT_DMA_OPS=y
CONFIG_XEN_VIRTIO=y

It is possible to copy these options into a .config file and then use make olddefconfig to build the rest of the kernel configuration, which you can then use to build a kernel as desired.

The linux-kernel-oci repository provides some example configurations and can generate a Dockerfile which will build a kernel image.

Minimum requirements for a host kernel

The configuration options above are also required for a host kernel. In addition, the following options are also required:

CONFIG_XEN_PV_DOM0=y
CONFIG_XEN_DOM0=y
CONFIG_PCI_XEN=y
CONFIG_XEN_PCIDEV_BACKEND=y
CONFIG_XEN_BLKDEV_BACKEND=y
CONFIG_XEN_NETDEV_BACKEND=y
CONFIG_XEN_SCSI_BACKEND=y
CONFIG_XEN_PVCALLS_BACKEND=y
CONFIG_TCG_XEN=m
CONFIG_XEN_WDT=y
CONFIG_XEN_DEV_EVTCHN=y
CONFIG_XEN_GNTDEV=y
CONFIG_XEN_GRANT_DEV_ALLOC=y
CONFIG_XEN_GRANT_DMA_ALLOC=y
CONFIG_SWIOTLB_XEN=y
CONFIG_XEN_PRIVCMD=y
CONFIG_XEN_ACPI_PROCESSOR=y
CONFIG_XEN_MCE_LOG=y

Build and install the kernel as you normally would for your system. Assuming GRUB is the bootloader, it will automatically detect the new host kernel when you run grub-mkconfig or grub2-mkconfig.

4.1 KiB Raw Blame History