Comment 10 for bug 1788665

Whew, after some hurdles I managed to install a Linux Mint 19 guest (Ubuntu 18.04). After all updates, here the output:

$ dmesg | grep microcode
[ 0.036780] core: PEBS disabled due to CPU errata, please upgrade microcode

So the microcode in the guest is not loaded! But see below:

$ cat /proc/cpuinfo | grep flags
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss ht syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology cpuid pni pclmulqdq vmx ssse3 cx16 pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx hypervisor lahf_lm cpuid_fault pti ssbd ibrs ibpb tpr_shadow vnmi flexpriority ept vpid tsc_adjust xsaveopt arat

Here is the qemu command I use for this Linux guest (it is almost identical to the Windows 10 VM command):

qemu-system-x86_64 \
  -runas user \
  -monitor stdio \
  -serial none \
  -parallel none \
  -nodefaults \
  -nodefconfig \
  -name $vmname,process=$vmname \
  -machine q35,accel=kvm,kernel_irqchip=on \
-cpu host,kvm=off,hv_vendor_id=1234567890ab,hv_vapic,hv_time,hv_relaxed,hv_spinlocks=0x1fff \
  -smp 6,sockets=1,cores=3,threads=2 \
  -m 16G \
  -mem-path /dev/hugepages \
  -mem-prealloc \
  -balloon none \
  -rtc base=localtime,clock=host \
  -vga none \
  -nographic \
  -soundhw hda \
  -device vfio-pci,host=02:00.0,multifunction=on \
  -device vfio-pci,host=02:00.1 \
  -device vfio-pci,host=00:1a.0 \
  -device vfio-pci,host=08:00.0 \
  -drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_CODE.fd \
  -drive if=pflash,format=raw,file=/tmp/my_vars.fd \
  -boot order=c \
  -drive id=disk0,if=virtio,cache=none,format=raw,file=/home/user/win.img \
  -netdev type=tap,id=net0,ifname=vmtap0,vhost=on \
  -device virtio-net-pci,netdev=net0,mac=00:16:3e:00:01:01

Kernel: 4.15.0-33-generic x86_64

$ grep microcode /proc/cpuinfo
microcode : 0x1
microcode : 0x1
microcode : 0x1
microcode : 0x1
microcode : 0x1
microcode : 0x1

In essence:
The microcode is NOT loaded in the Linux VM. However, the following feature flags are listed: "pti ssbd ibrs ibpb". The "stibp" flag is missing.

Hope this helps.