I am using nested virtualization on a Google Cloud Compute instance. Things are generally working fine with libvirt using qemu+kvm, however I observed that <cpu mode='host-model'> is not exposing avx and avx2 instruction set to the guest Linux instance. Google Cloud platform claims the CPU model of the host compute instance is Broadwell, however libvirt capabilities maps it to Westmere-IBRS and it has avx and avx2 features, yet host-model is not exposing those. 

As a workaround, I am using <cpu mode='host-passthrough'>, but I would like to know what is going wrong here? I can also share the output of cpuid of the host system, if that helps.  I am not sure whether it's a libvirt issue or something to do with KVM. Any help would be appreciated. 

Following is the host information, along with the qemu process details for the linux guest. 

root@dev-vm:~# kvm --version

QEMU emulator version 2.8.1(Debian 1:2.8+dfsg-6+deb9u9)

Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developers

root@dev-vm:~# virsh --version

setlocale: No such file or directory

3.0.0

root@dev-vm:~# virsh capabilities

<capabilities>

  <host>

    <uuid>a2b6c5d9-dfea-7efb-defb-3cce3aadb067</uuid>

    <cpu>

      <arch>x86_64</arch>

      <model>Westmere-IBRS</model>

      <vendor>Intel</vendor>

      <topology sockets='1' cores='4' threads='2'/>

      <feature name='vme'/>

      <feature name='ss'/>

      <feature name='ht'/>

      <feature name='pclmuldq'/>

      <feature name='vmx'/>

      <feature name='fma'/>

      <feature name='pcid'/>

      <feature name='x2apic'/>

      <feature name='movbe'/>

      <feature name='xsave'/>

      <feature name='osxsave'/>

      <feature name='avx'/>

      <feature name='f16c'/>

      <feature name='rdrand'/>

      <feature name='hypervisor'/>

      <feature name='arat'/>

      <feature name='fsgsbase'/>

      <feature name='tsc_adjust'/>

      <feature name='bmi1'/>

      <feature name='hle'/>

      <feature name='avx2'/>

      <feature name='smep'/>

      <feature name='bmi2'/>

      <feature name='erms'/>

      <feature name='invpcid'/>

      <feature name='rtm'/>

      <feature name='rdseed'/>

      <feature name='adx'/>

      <feature name='smap'/>

      <feature name='md-clear'/>

      <feature name='ssbd'/>

      <feature name='xsaveopt'/>

      <feature name='pdpe1gb'/>

      <feature name='rdtscp'/>

      <feature name='abm'/>

      <feature name='3dnowprefetch'/>

      <feature name='invtsc'/>

      <pages unit='KiB' size='4'/>

      <pages unit='KiB' size='2048'/>

      <pages unit='KiB' size='1048576'/>

    </cpu>

    <power_management>

      <suspend_mem/>

      <suspend_disk/>

      <suspend_hybrid/>

    </power_management>

    <migration_features>

      <live/>

      <uri_transports>

        <uri_transport>tcp</uri_transport>

15771 ?        Sl     0:03 qemu-system-x86_64 -enable-kvm -name guest=Util-LIN-1,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-11-Util-LIN-1/master-key.aes -machine pc-i440fx-2.1,accel=kvm,usb=off,dump-guest-core=off -cpu Westmere-IBRS,+vme,+ss,+ht,+pclmuldq,+vmx,+fma,+pcid,+x2apic,+movbe,+xsave,+osxsave,+avx,+f16c,+rdrand,+hypervisor,+arat,+fsgsbase,+tsc_adjust,+bmi1,+hle,+avx2,+smep,+bmi2,+erms,+invpcid,+rtm,+rdseed,+adx,+smap,+md-clear,+ssbd,+xsaveopt,+pdpe1gb,+rdtscp,+abm,+3dnowprefetch -m 4096 -realtime mlock=off -smp 4,sockets=4,cores=1,threads=1 -uuid caa60e3c-f946-40a4-80ac-1fb86366c5f6 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-11-Util-LIN-1/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device ahci,id=sata0,bus=pci.0,addr=0x4 -drive file=/var/lib/libvirt/images/Util-LIN-1/Util-LIN-1.qcow2,format=qcow2,if=none,id=drive-sata0-0-0 -device ide-hd,bus=sata0.0,drive=drive-sata0-0-0,id=sata0-0-0,bootindex=1 -drive file=/var/lib/libvirt/images/Util-LIN-1/Util-LIN-1-acdisk.qcow2,format=qcow2,if=none,id=drive-sata0-0-2 -device ide-hd,bus=sata0.2,drive=drive-sata0-0-2,id=sata0-0-2 -netdev tap,fd=34,id=hostnet0,vhost=on,vhostfd=36 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=1a:b2:ae:f7:69:c7,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device usb-tablet,id=input0,bus=usb.0,port=1 -vnc 0.0.0.0:8 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -incoming defer -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 -msg timestamp=on