nested virtualization with KVM: -enable-kvm in qemu in nested virtualization
In my already virtualized host, trying to pass the option the option -enable-kvm -m 1024, will fail:
qemu-system-x86_64 -vga std -enable-kvm -m 1024 -monitor telnet:localhost:9313,server,nowait -drive file=my_img.img,cache=none
# Could not access KVM kernel module: No such file or directory
# failed to initialize KVM: No such file or directory
If I remove that option -enable-kvm -m 1024, qemu will load (but it will take forever, because it is using software emulation):
qemu-system-x86_64 -vga std -monitor telnet:localhost:9313,server,nowait -drive file=my_img.img,cache=none
# qemu running, OK, but image taking forever to load.
Surely, this virtualized host of mine has capabilities of nesting its own virtualization. Everywhere I find information about it [like here: https://docs.openstack.org/developer/devstack/guides/devstack-with-nested-kvm.html ] tells me that I must check the file /sys/module/kvm_intel/parameters/nested which is simply not available, because kvm-intel isn't and can't be loaded from inside an image:
sudo modprobe kvm-intel
# modprobe: ERROR: could not insert 'kvm_intel': Operation not supported
Probably that method of debugging nested virtualization only works in the bare metal. So, how do I enable (forward the support of) kvm from inside a kvm?
Additional info:
lscpu # from inside the virtualized host
# Architecture: x86_64
# ...
# Vendor ID: GenuineIntel
# CPU family: 6
# Model: 13
# Model name: QEMU Virtual CPU version (cpu64-rhel6)
# Stepping: 3
# ...
# Hypervisor vendor: KVM
ltrace of qemu:
# open64("/dev/kvm", 524290, 00) = -1
# __errno_location() = 0x7f958673c730
# __fprintf_chk(0x7f957fd81060, 1, 0x7f9586474ce0, 0Could not access KVM kernel module: No such file or directory
Answer
To test if the kvm support is enabled in the current host (ie, it works in the virtual machine) do:
grep -E "(vmx|svm)" /proc/cpuinfo
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc extd_apicid aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 popcnt aes xsave avx f16c lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce tbm topoext perfctr_core perfctr_nb arat cpb hw_pstate npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold vmmcall bmi1
In the question:
grep -E "(vmx|svm)" /proc/cpuinfo | wc -l
0
It means that the support is disabled, and enable-kvm won't work. Action in the bare metal machine is required.