Title: KVM guest on AMD EPYC 9475F: TSC marked unstable despite clocksource=tsc, how to make TSC work with Xenomai kernel?

We run Linux guests (kernel 6.1, 16 vCPUs) on Proxmox/KVM with AMD EPYC 9475F. The guest requires TSC as the clocksource, but the kernel marks it unstable at boot:

Available clock sources become only kvm-clock acpi_pm and no tsc.

Tried cpu: host, cpu: EPYC, +invtsc flag, -global kvm-clock.present=0, none make TSC available. The same image works fine on Intel Xeon hosts.

Is tsc=reliable kernel parameter safe under KVM to bypass this check? Or is there a QEMU/KVM-level fix to properly synchronize TSC across vCPUs on AMD EPYC?