linux: running self compiled kernel in qemu: VFS: Unable to mount root fs on unknown wn-block(0,0)

I figured it out by myself. Some time has passed, but as I recall the solution was to provide an initial ramdisk. This is how I got it working with hardware acceleration.

Compiling

make defconfig

CONFIG_EXT4_FS=y
CONFIG_IA32_EMULATION=y
CONFIG_VIRTIO_PCI=y (Virtualization -> PCI driver for virtio devices)
CONFIG_VIRTIO_BALLOON=y (Virtualization -> Virtio balloon driver)
CONFIG_VIRTIO_BLK=y (Device Drivers -> Block -> Virtio block driver)
CONFIG_VIRTIO_NET=y (Device Drivers -> Network device support -> Virtio network driver)
CONFIG_VIRTIO=y (automatically selected)
CONFIG_VIRTIO_RING=y (automatically selected)

---> see http://www.linux-kvm.org/page/Virtio

Enable paravirt in config

Disable NMI watchdog on HOST for using performance counters on GUEST. You may ignore this.

cat /proc/sys/kernel/nmi_watchdog

---> see http://kvm.et.redhat.com/page/Guest_PMU

Start in Qemu

sudo qemu-system-x86_64 -m 1024M -hda /var/lib/libvirt/images/DEbian.img -enable-kvm -initrd /home/username/compiled_kernel/initrd.img-3.2.46 -kernel /home/username/compiled_kernel/bzImage -append "root=/dev/sda1 console=ttyS0" -nographic -redir tcp:2222::22 -cpu host -smp cores=2

Start in KVM

Kernal path: /home/username/compiled_kernel/bzImage
Initrd path: /home/username/compiled_kernel/initrd.img-3.2.46
Kernel arguments: root=/dev/sda1

Hope this helps if someone has the same issues.