generic arm64 kernel can not boot initrdless and there is no -kvm kernel

[Thomas Bechtold]

The CPC team wants to build minimal arm64 images. Those images should boot initrdless (similar to the amd64 images where the -kvm kernel is used).
But booting an initrdless image (build with livecd-rootfs) does fail with:

$ sudo qemu-system-aarch64 -m 2G -M virt -cpu max -bios /usr/share/qemu-efi-aarch64/QEMU_EFI.fd -drive if=none,format=qcow2,file=livecd.ubuntu-cpc.img,id=hd0 -device virtio-blk-device,drive=hd0 -device e1000,netdev=net0 -netdev user,id=net0,hostfwd=tcp:127.0.0.1:5555-:22 -nographic

[snipped]

[ 0.945928] VFS: Cannot open root device "PARTUUID=15058d73-bec1-4c7d-9cd7-f0f73f3ec694" or unknown-block(0,0): error -6
[ 0.946117] Please append a correct "root=" boot option; here are the available partitions:
[ 0.947611] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 0.948139] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-74-generic #83-Ubuntu
[ 0.948237] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[ 0.948453] Call trace:
[ 0.948736] dump_backtrace+0x0/0x190
[ 0.948864] show_stack+0x28/0x38
[ 0.948918] dump_stack+0xb4/0x10c
[ 0.948974] panic+0x150/0x364
[ 0.949027] mount_block_root+0x248/0x304
[ 0.949090] mount_root+0x48/0x50
[ 0.949145] prepare_namespace+0x13c/0x1bc
[ 0.949205] kernel_init_freeable+0x270/0x2c4
[ 0.949274] kernel_init+0x1c/0x114
[ 0.949336] ret_from_fork+0x10/0x18
[ 0.949913] Kernel Offset: disabled
[ 0.950175] CPU features: 0x0952,20e0a230
[ 0.950251] Memory Limit: none
[ 0.950595] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---

The reason is, that the the virtio drivers are modules (CONFIG_VIRTIO_BLK=m) but for initrdless boot, they need to be compiled into the kernel.

Expected behavior:
Booting an arm64 image without an initrd does work in a virtualized environment similar to an amd64 image (that uses the -kvm kernel)

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1931841

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.