systemd-detect-virt: Incorrectly identifies KVM VMs when using hv_passthrough

[holmanb]

systemd version the issue has been seen with
249.9

Used distribution
Ubuntu Jammy (22.04)

Linux kernel version used (uname -a)
Linux ubuntu 5.15.0-18-generic #18-Ubuntu SMP Fri Jan 21 14:57:54 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

CPU architecture issue was seen on
x86_64

Expected behaviour you didn't see
systemd-detect-virt should identify KVM-accelerated VMs as "kvm" or something indicating that KVM is in use

Unexpected behaviour you saw
systemd-detect-virt identifies KVM-accelerated VMs as "qemu" when hv_passthrough is used

Steps to reproduce the problem

#!/bin/sh

wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img

# cloud-config sets user password
cat >user-data <<EOF
#cloud-config
password: password
chpasswd:
  expire: False
EOF

# requires package cloud-utils, adds user/password to cloud image
cloud-localds seed.img user-data

# The second invocation uses hv_passthrough, which causes systemd-detect-virt to report "qemu" as the virtualization method
# Log in and execute `systemd-detect-virt`
#
# Moniker: ubuntu
# Password: password
#

# Works as expected:
qemu-system-x86_64 -net nic -net user -machine accel=kvm,type=q35 -cpu host -m 512 -nographic -hda jammy-server-cloudimg-amd64.img -hdb seed.img

# Reports "qemu" as virtualization type
qemu-system-x86_64 -net nic -net user -machine accel=kvm,type=q35 -cpu host,hv_passthrough -m 512 -nographic -hda jammy-server-cloudimg-amd64.img -hdb seed.img

Additional program output to the terminal or log subsystem illustrating the issue

# without hv_passthrough:

ubuntu@ubuntu:~$  SYSTEMD_LOG_LEVEL=debug systemd-detect-virt
Failed to read $container of PID 1, ignoring: Permission denied
Found cgroup2 on /sys/fs/cgroup/, full unified hierarchy
Found container virtualization none.
Virtualization QEMU found in DMI (/sys/class/dmi/id/sys_vendor)
UML virtualization not found in /proc/cpuinfo.
Virtualization found, CPUID=KVMKVMKVM
Found VM virtualization kvm
kvm


# with hv_passthrough (incorrect identification)
ubuntu@ubuntu:~$ SYSTEMD_LOG_LEVEL=debug systemd-detect-virt
Failed to read $container of PID 1, ignoring: Permission denied
Found cgroup2 on /sys/fs/cgroup/, full unified hierarchy
Found container virtualization none.
Virtualization QEMU found in DMI (/sys/class/dmi/id/sys_vendor)
UML virtualization not found in /proc/cpuinfo.
Virtualization found, CPUID=Linux KVM Hv
Found VM virtualization qemu
qemu

[holmanb]

Fixed in #22945

[poettering]

Is this just a duplicate of #17894?