Bug 1779078

Also can reproduce on 4.4 engine.
ovirt-engine-4.4.0-0.6.master.el7.noarch

Created attachment 1642259 [details]
cpuinfo

Thank you. It's clearer now.
Apparently domcaps is saying that Haswell(the one with TSX) is supported guest CPU. Jiri, any idea why? cpas is saying it's noTSX, cpu flags do not have hle,rtm, so why is libvirt saying "Haswell" is a valid type?

@cshao, as a workaround you can easily select Haswell-noTSX as a Cluster CPU type and VMs should work just fine. It's just the autodetection that selects a non-working model by default.

(In reply to Michal Skrivanek from comment #25)
> @cshao, as a workaround you can easily select Haswell-noTSX as a Cluster CPU
> type and VMs should work just fine. It's just the autodetection that selects
> a non-working model by default.

You are right.
VM can run successful after selected Haswell-noTSX as a Cluster CPU type.

Thanks.

Sigh, this mess is a result of versioned CPU models introduced in QEMU 4.1.0
without proper support for introspection (see bug 1697663, mainly in comments
4, 5, and 6) and thus no support for this in libvirt. Unfortunately, it seems
the needed machine type parameter for query-cpu-definitions QMP command is not
present even in QEMU v4.2.0-rc4.

Anyway, libvirt probes for supported CPU models and their usability on the
current host by probing QEMU with machine type "none". In this case, QEMU
reports "Haswell" CPU model is in fact an alias of "Haswell-v4"
("Haswell-noTSX-IBRS" using the original naming) and thus it is marked as
runnable as it does not require the TSX features. See below for the QMP log.

If I try to probe QEMU with machine type pc-i440fx-rhel7.6.0, which is the
default machine used when starting a domain, I get a completely different
results (see the second QMP log). The "Haswell" CPU model is not runnable
anymore because of missing "hle" and "rtm" features. Also I don't see any
"alias-of" fields there (currently unused by libvirt, though).

I don't know what the right fix should be here, but until bug 1697663 is fully
implemented and libvirt starts using it, the CPU model introspection is
completely broken.


# /usr/libexec/qemu-kvm -machine none -nodefaults -nographic -qmp unix:/tmp/ble,server &
# socat STDIO UNIX-CONNECT:/tmp/ble
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 4}, "package": "qemu-kvm-4.1.0-14.module+el8.1.0+4548+ed1300f4"}, "capabilities": ["oob"]}}
{"execute": "qmp_capabilities"}
{"return": {}}
{"execute": "query-cpu-definitions"}
{
    "return": [
        ...
        {
            "name": "Haswell-v4",
            "typename": "Haswell-v4-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v3",
            "typename": "Haswell-v3-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v2",
            "typename": "Haswell-v2-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v1",
            "typename": "Haswell-v1-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-noTSX-IBRS",
            "typename": "Haswell-noTSX-IBRS-x86_64-cpu",
            "unavailable-features": [
            ],
            "alias-of": "Haswell-v4",
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-noTSX",
            "typename": "Haswell-noTSX-x86_64-cpu",
            "unavailable-features": [
            ],
            "alias-of": "Haswell-v2",
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-IBRS",
            "typename": "Haswell-IBRS-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "alias-of": "Haswell-v3",
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell",
            "typename": "Haswell-x86_64-cpu",
            "unavailable-features": [
            ],
            "alias-of": "Haswell-v4",
            "static": false,
            "migration-safe": true
        },
        ...
    ]
}


# /usr/libexec/qemu-kvm -machine pc-i440fx-rhel7.6.0 -nodefaults -nographic -qmp unix:/tmp/ble,server &
# socat STDIO UNIX-CONNECT:/tmp/ble
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 1, "major": 4}, "package": "qemu-kvm-4.1.0-14.module+el8.1.0+4548+ed1300f4"}, "capabilities": ["oob"]}}
{"execute": "qmp_capabilities"}
{"return": {}}
{"execute": "query-cpu-definitions"}
{
    "return": [
        ...
        {
            "name": "Haswell-v4",
            "typename": "Haswell-v4-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v3",
            "typename": "Haswell-v3-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v2",
            "typename": "Haswell-v2-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-v1",
            "typename": "Haswell-v1-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-noTSX-IBRS",
            "typename": "Haswell-noTSX-IBRS-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-noTSX",
            "typename": "Haswell-noTSX-x86_64-cpu",
            "unavailable-features": [
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell-IBRS",
            "typename": "Haswell-IBRS-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        {
            "name": "Haswell",
            "typename": "Haswell-x86_64-cpu",
            "unavailable-features": [
                "hle",
                "rtm"
            ],
            "static": false,
            "migration-safe": true
        },
        ...
    ]
}

Fix submitted upstream:
https://lore.kernel.org/qemu-devel/20191205223339.764534-1-ehabkost@redhat.com/

      <model usable='yes'>Haswell-noTSX-IBRS</model>
      <model usable='yes'>Haswell-noTSX</model>
      <model usable='no'>Haswell-IBRS</model>
      <model usable='no'>Haswell</model>

seems to work well. Thanks Eduardo!

QA_ACK, please?

QEMU has been recently split into sub-components and as a one-time operation to avoid breakage of tools, we are setting the QEMU sub-component of this BZ to "General". Please review and change the sub-component if necessary the next time you review this BZ. Thanks

Reproduce:
qemu-kvm-4.2.0-9.module+el8.2.0+5699+b5331ee5
libvirt-client-6.0.0-7.module+el8.2.0+5869+c23fe68b.x86_64
kernel-4.18.0-179.el8.x86_64

host: dell-per730-28.lab.eng.pek2.redhat.com (Intel(R) Xeon(R) CPU E5-2609 v3 @ 1.90GHz)

Haswell is usable in `virsh domcapabilities` while host doesn't support hle and rtm.

# virsh domcapabilities
  <cpu>
    <mode name='host-passthrough' supported='yes'/>
    <mode name='host-model' supported='yes'>
      <model fallback='forbid'>Haswell-noTSX-IBRS</model>
      <vendor>Intel</vendor>
      ...
    </mode>
    <mode name='custom' supported='yes'>
      ...
      <model usable='yes'>Haswell-noTSX-IBRS</model>
      <model usable='yes'>Haswell-noTSX</model>
      <model usable='no'>Haswell-IBRS</model>
      <model usable='yes'>Haswell</model>             ---------> Haswell is usable
      ...
    </mode>
  </cpu>

# /usr/libexec/qemu-kvm -cpu Haswell
qemu-kvm: warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
qemu-kvm: warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]



Verify:
qemu-kvm-4.2.0-12.module+el8.2.0+5858+afd073bc
libvirt-client-6.0.0-7.module+el8.2.0+5869+c23fe68b.x86_64
kernel-4.18.0-179.el8.x86_64

On same host, Haswell is not usable anymore.

# virsh domcapabilities | grep -A80 '<cpu'
  <cpu>
    <mode name='host-passthrough' supported='yes'/>
    <mode name='host-model' supported='yes'>
      <model fallback='forbid'>Haswell-noTSX-IBRS</model>
      <vendor>Intel</vendor>
      ...
    </mode>
    <mode name='custom' supported='yes'>
      ...
      <model usable='yes'>Haswell-noTSX-IBRS</model>
      <model usable='yes'>Haswell-noTSX</model>
      <model usable='no'>Haswell-IBRS</model>
      <model usable='no'>Haswell</model>      ----------> Haswell is not usable.
      ...
    </mode>
  </cpu>

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:2017