[libvirt PATCH 0/9] [RFC] Dynamic CPU models

[Tim Wiederhake]

See below.
What do the more experienced libvirt developers think, is this going in
the right direction?

Thanks,
Tim

On Tue, 2022-06-28 at 18:09 +0200, Tim Wiederhake wrote:
> libvirt and qemu cpu models are out of sync. libvirt cpu models are
> considered static and never changing, whereas qemu cpu models have
> changed over time. This leads to problems and confusion for users,
> as the cpu models they specify may have different features than what
> they expect.
> 
> This series introduces two new APIs to enumerate and retrieve cpu
> models dynamically from the hypervisor at runtime, allowing the user
> to make use of cpu models from newer hypervisor versions even if
> libvirt is not aware of them.
> 
> These two new functions are intended as building blocks onto which
> higher-level functionality can be build, e.g. the ability to specify
> a hypervisor cpu model directly in a domain xml. With these two
> functions alone this has to be done manually for now, i.e. enumerate
> the available cpu models, retrieve the cpu description and manually
> insert it into the domain xml accordingly:
> 
>     $ virsh hypervisor-cpu-models --arch x86_64
>     Name                        Alias
>     ----------------------------------------------------
>     max
>     host
>     base
>     qemu64-v1
>     qemu64                      qemu64-v1
>     qemu32-v1
>     qemu32                      qemu32-v1
>     phenom-v1
>     phenom                      phenom-v1
>     (...)
> 
>     $ virsh hypervisor-cpu-definition --machine pc --arch x86_64
> qemu64
>     <cpu>
>       <model>qemu64</model>
>       <feature name='cmov'/>
>       <feature name='mmx'/>
>       <feature name='xd'/>
>       <feature name='x-intel-pt-auto-level'/>
>       <feature name='kvm_asyncpf'/>
>       <feature name='kvm-asyncpf'/>
>       <feature name='legacy-cache'/>
>       <feature name='vmware-cpuid-freq'/>
>       <feature name='mce'/>
>       <feature name='mca'/>
>       <feature name='msr'/>
>       <feature name='fxsr'/>
>       <feature name='cpuid-0xb'/>
>       <feature name='kvm_pv_eoi'/>
>       <feature name='pni'/>
>       <feature name='x2apic'/>
>       <feature name='i64'/>
>       <feature name='pae'/>
>       <feature name='pat'/>
>       <feature name='sse'/>
>       <feature name='kvm_nopiodelay'/>
>       <feature name='kvm-nopiodelay'/>
>       <feature name='kvmclock-stable-bit'/>
>       <feature name='hypervisor'/>
>       <feature name='syscall'/>
>       <feature name='x-migrate-smi-count'/>
>       <feature name='full-cpuid-auto-level'/>
>       <feature name='sse3'/>
>       <feature name='sse2'/>
>       <feature name='kvm-pv-eoi'/>
>       <feature name='cx8'/>
>       <feature name='pge'/>
>       <feature name='fill-mtrr-mask'/>
>       <feature name='cx16'/>
>       <feature name='de'/>
>       <feature name='clflush'/>
>       <feature name='tsc'/>
>       <feature name='fpu'/>
>       <feature name='check'/>
>       <feature name='apic'/>
>       <feature name='kvm-steal-time'/>
>       <feature name='kvm_steal_time'/>
>       <feature name='kvmclock'/>
>       <feature name='l3-cache'/>
>       <feature name='nx'/>
>       <feature name='tcg-cpuid'/>
>       <feature name='lm'/>
>       <feature name='pse'/>
>       <feature name='sep'/>
>       <feature name='kvm'/>
>       <feature name='lahf-lm'/>
>       <feature name='lahf_lm'/>
>       <feature name='mtrr'/>
>       <feature name='pse36'/>
>     </cpu>
> 
> The returned cpu description is currently completely unfiltered, as
> can be seen by the duplicate entries differing only in "-" vs. "_"
> usage, inclusion of experimental feature flags and generally, flags
> that are not recognized by libvirt. One possibility to adress this
> would be to extend virQEMUCapsCPUFeatureTranslate.
> 
> Before I continue with this, I would love to hear other people's
> thoughts, comments and potential use cases.
> 
> Cheers,
> Tim
> 
> Tim Wiederhake (9):
>   qemuMonitorCPUDefInfo: Add alias
>   libvirt: introduce virConnectGetHypervisorCPUModelNames public API
>   remote: Add RPC support for the
> virConnectGetHypervisorCPUModelNames
>     API
>   qemu: implement virConnectGetHypervisorCPUModelNames API
>   tools: Report hypervisor cpu model names
>   libvirt: introduce virConnectGetHypervisorCPUModelDefinition public
>     API
>   remote: Add support for the
> virConnectGetHypervisorCPUModelDefinition
>     API
>   qemu: Implement virConnectGetHypervisorCPUModelDefinition API
>   tools: Report hypervisor cpu model definitions
> 
>  docs/manpages/virsh.rst             |  27 ++++++
>  include/libvirt/libvirt-host.h      |  13 +++
>  src/driver-hypervisor.h             |  17 ++++
>  src/libvirt-host.c                  | 109 +++++++++++++++++++++++
>  src/libvirt_public.syms             |   2 +
>  src/qemu/qemu_driver.c              | 105 ++++++++++++++++++++++
>  src/qemu/qemu_monitor.c             |   2 +
>  src/qemu/qemu_monitor.h             |   1 +
>  src/qemu/qemu_monitor_json.c        |   3 +
>  src/remote/remote_daemon_dispatch.c |  76 ++++++++++++++++
>  src/remote/remote_driver.c          | 100 +++++++++++++++++++++
>  src/remote/remote_protocol.x        |  37 +++++++-
>  src/remote_protocol-structs         |  27 ++++++
>  tools/virsh-host.c                  | 132
> ++++++++++++++++++++++++++++
>  14 files changed, 650 insertions(+), 1 deletion(-)
> 
> -- 
> 2.31.1
> 
>