[Bug 2084102] Re: Sapphire rapids not recognized by virsh capabilities

[Christian Ehrhardt]

Hi,
it is a limitation - and always was - that others (like in this case openstack) treat host-capabilities CPU name as something it isn't - a name vs an approximation of the CPU.

I'm glad upstream now documented it after working with them on getting
this finally more outspoken.

Libvirt would never want you to say "CPU name" and more likely "Name +/- features".
Which is just what libvirt does when it is asked to express the host model.

I thought Openstack does support host-model [1], which can be the
easiest but only good if you have consistent CPUs across all your nodes.
But it also has custom [2], which allows the use of CPU Features [3]
mostly in the same way that libvirt does.

Due to that - no matter if security issues, CPU errata and more change
the features after a name was defined. You can still express "any-name +
features" there as well and thereby get all the new CPU features right?
(host-model would do the same for you, but if you want a common
denominator you can define it via custom+flags here).

Adding a few openstack people to the bug to get their POV to all of
this.

[1]: https://docs.openstack.org/nova/latest/admin/cpu-models.html#host-model
[2]: https://docs.openstack.org/nova/latest/admin/cpu-models.html#custom
[3]: https://docs.openstack.org/nova/latest/admin/cpu-models.html#cpu-feature-flags

** Also affects: nova (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/2084102

Title:
  Sapphire rapids not recognized by virsh capabilities

Status in libvirt package in Ubuntu:
  Won't Fix
Status in nova package in Ubuntu:
  New

Bug description:
  On Ubuntu Noble 24.04, on a Intel Sapphire rapids CPU equipped
  platform, when i run

  virsh capabilities

  it does not detect the right CPU model:

  <capabilities>
    <host>
      <uuid>cfae836f-0098-475d-9924-8de9d69a5c98</uuid>
      <cpu>
        <arch>x86_64</arch>
        <model>Broadwell-noTSX-IBRS</model>
        <vendor>Intel</vendor>
        <microcode version='721421777'/>
        <signature family='6' model='143' stepping='8'/>
        <counter name='tsc' frequency='2400000000' scaling='yes'/>
        <topology sockets='1' dies='1' cores='48' threads='2'/>
        <maxphysaddr mode='emulate' bits='45'/>

  
  I expect the model SapphireRapids or SapphireRapids-noTSX or SapphireRapids-noTSX-IBRS to be shown.

  Here is the lscpu output:

  
  Architecture:             x86_64
    CPU op-mode(s):         32-bit, 64-bit
    Address sizes:          45 bits physical, 57 bits virtual
    Byte Order:             Little Endian
  CPU(s):                   192
    On-line CPU(s) list:    0-191
  Vendor ID:                GenuineIntel
    Model name:             Intel(R) Xeon(R) Platinum 8488C
      CPU family:           6
      Model:                143
      Thread(s) per core:   2
      Core(s) per socket:   48
      Socket(s):            2
      Stepping:             8
      CPU(s) scaling MHz:   21%
      CPU max MHz:          3800.0000
      CPU min MHz:          800.0000
      BogoMIPS:             4800.00
      Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 
                            ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology no
                            nstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fm
                            a cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand la
                            hf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cat_l2 cdp_l3 tdx_host_platform intel_ppin cdp_l2 ssbd mba i
                            brs ibpb stibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_ad fsgsbase tsc_adjust sgx bmi1 avx2 smep
                             bmi2 erms invpcid cqm rdt_a avx512f avx512dq rdseed adx smap avx512ifma clflushopt clwb intel_pt avx512cd 
                            sha_ni avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local s
                            plit_lock_detect user_shstk avx_vnni avx512_bf16 wbnoinvd dtherm ida arat pln pts hwp hwp_act_window hwp_ep
                            p hwp_pkg_req hfi vnmi avx512vbmi umip pku ospke waitpkg avx512_vbmi2 gfni vaes vpclmulqdq avx512_vnni avx5
                            12_bitalg tme avx512_vpopcntdq la57 rdpid bus_lock_detect cldemote movdiri movdir64b enqcmd sgx_lc fsrm md_
                            clear serialize tsxldtrk pconfig arch_lbr ibt amx_bf16 avx512_fp16 amx_tile amx_int8 flush_l1d arch_capabil
                            ities
  Virtualization features:  
    Virtualization:         VT-x
  Caches (sum of all):      
    L1d:                    4.5 MiB (96 instances)
    L1i:                    3 MiB (96 instances)
    L2:                     192 MiB (96 instances)
    L3:                     210 MiB (2 instances)
  NUMA:                     
    NUMA node(s):           2
    NUMA node0 CPU(s):      0-47,96-143
    NUMA node1 CPU(s):      48-95,144-191
  Vulnerabilities:          
    Gather data sampling:   Not affected
    Itlb multihit:          Not affected
    L1tf:                   Not affected
    Mds:                    Not affected
    Meltdown:               Not affected
    Mmio stale data:        Not affected
    Reg file data sampling: Not affected
    Retbleed:               Not affected
    Spec rstack overflow:   Not affected
    Spec store bypass:      Mitigation; Speculative Store Bypass disabled via prctl
    Spectre v1:             Mitigation; usercopy/swapgs barriers and __user pointer sanitization
    Spectre v2:             Mitigation; Enhanced / Automatic IBRS; IBPB conditional; RSB filling; PBRSB-eIBRS SW sequence; BHI BHI_DIS_
                            S
    Srbds:                  Not affected
    Tsx async abort:        Not affected

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