Comment 26 for bug 1921880

Before state as in LP#1921754 (linux 5.11.0-16-generic, qemu 1:5.2+dfsg-9ubuntu2, libvirt 7.0.0-2ubuntu1)

With proposed:

# qemu-system-x86_64 -cpu ? | grep EPYC-Milan
x86 EPYC-Milan (alias configured by machine type)
x86 EPYC-Milan-v1 AMD EPYC-Milan Processor

# virsh domcapabilities
...
    <mode name='host-model' supported='yes'>
      <model fallback='forbid'>EPYC-Milan</model>
      <vendor>AMD</vendor>
      <feature policy='require' name='x2apic'/>
      <feature policy='require' name='tsc-deadline'/>
      <feature policy='require' name='hypervisor'/>
      <feature policy='require' name='tsc_adjust'/>
      <feature policy='require' name='vaes'/>
      <feature policy='require' name='vpclmulqdq'/>
      <feature policy='require' name='spec-ctrl'/>
      <feature policy='require' name='stibp'/>
      <feature policy='require' name='arch-capabilities'/>
      <feature policy='require' name='ssbd'/>
      <feature policy='require' name='cmp_legacy'/>
      <feature policy='require' name='invtsc'/>
      <feature policy='require' name='virt-ssbd'/>
      <feature policy='require' name='rdctl-no'/>
      <feature policy='require' name='skip-l1dfl-vmentry'/>
      <feature policy='require' name='mds-no'/>
      <feature policy='require' name='pschange-mc-no'/>
      <feature policy='disable' name='svme-addr-chk'/>
    </mode>
...

Launching a guest with with EPYC-Milan works:

# cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 25
model : 1
model name : AMD EPYC-Milan Processor
stepping : 1
microcode : 0x1000065
cpu MHz : 2445.404
cache size : 512 KB
physical id : 0
siblings : 2
core id : 0
cpu cores : 1
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
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 rep_good nopl cpuid extd_apicid tsc_known_freq pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm cmp_legacy svm cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw topoext perfctr_core invpcid_single ssbd ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves clzero xsaveerptr wbnoinvd arat npt nrip_save umip pku ospke rdpid fsrm
bugs : sysret_ss_attrs spectre_v1 spectre_v2 spec_store_bypass
bogomips : 4890.80
TLB size : 1024 4K pages
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management: