[Qemu-discuss] Booting a QEMU instance within a QEMU instance using KVM doesn't work

[Kaushik Datta]

Hello all,

I am trying to show that KVM is working by booting a guest QEMU instance within 
a host QEMU instance using KVM.  To provide context, the host QEMU is 
translating x86 to aarch64, while the guest QEMU is translating aarch 64 to 
aarch64, so is a candidate for KVM acceleration.  I’m using QEMU 3.1.0 with the 
xlnx-versal-virt machine model for both the host and the guest since this is 
the only QEMU version + machine model combination that I’ve found that 
successfully initializes the KVM hypervisor (shown below).  In addition, both 
the host and the guest are using a Debian 4.9.130-2 kernel and a 
Yocto-generated rootfs.  Here is the command I use to launch the host QEMU 
instance:

qemu-system-aarch64 -M xlnx-versal-virt -m 2048 -cpu cortex-a53 -kernel 
vmlinuz-4.9.0-8-arm64 -initrd new_rootfs.cpio.gz -nographic -D 
"./qemu_debug.txt"

After the host QEMU boots, here is the dmesg output regarding KVM:

[   12.058077] kvm [1]: HYP VA range: 800000000000:ffffffffffff
[   12.061797] kvm [1]: Hyp mode initialized successfully

In addition, /dev/kvm exists and I’m operating as root, so that’s good.  
However, when I do lsmod, I get an empty output, which is a concern.  Anyway, 
this is the command I used to boot the guest QEMU instance with KVM 
acceleration within the host QEMU:

qemu-system-aarch64 -M xlnx-versal-virt -m 1024 -cpu cortex-a53 -kernel 
vmlinuz-4.9.0-8-arm64 -initrd new_rootfs.cpio.gz -accel kvm -enable-kvm 
-nographic -D "./qemu_debug.txt"

However, this is the error that I get:

qemu-system-aarch64: 
/home/kdatta/hpsc-bsp/HEAD/work/poky_build/tmp/work/aarch64-poky-linux/qemu/3.1.0-r0/qemu-3.1.0/exec.c:892:
 cpu_address_space_init: Assertion `asidx == 0 || !kvm_enabled()' failed.
[ 2083.334829] audit: type=1701 audit(1549051290.640:2): auid=4294967295 uid=0 
gid=0 ses=4294967295 pid=153 comm="qemu-system-aar" 
exe="/usr/bin/qemu-system-aarch64" sig=6
./boot_qemu.sh: line 8:   153 Aborted                 qemu-system-aarch64 -M 
xlnx-versal-virt -m 1024 -cpu cortex-a53 -kernel vmlinuz-4.9.0-8-arm64 -initrd 
new_rootfs.cpio.gz -accel kvm -enable-kvm -nographic -D "./qemu_debug.txt"

Any help would be appreciated.  I’m happy to answer questions as well.

Thanks,
Kaushik