Re: [PATCH v9] qapi: introduce 'query-kvm-cpuid' action

[Vladimir Sementsov-Ogievskiy]

03.06.2021 12:07, Valeriy Vdovin wrote:
> Introducing new qapi method 'query-kvm-cpuid'. This method can be used to
> get virtualized cpu model info generated by QEMU during VM initialization in
> the form of cpuid representation.
>
> Diving into more details about virtual cpu generation: QEMU first parses '-cpu'
> command line option. From there it takes the name of the model as the basis for
> feature set of the new virtual cpu. After that it uses trailing '-cpu' options,
> that state if additional cpu features should be present on the virtual cpu or
> excluded from it (tokens '+'/'-' or '=on'/'=off').
> After that QEMU checks if the host's cpu can actually support the derived
> feature set and applies host limitations to it.
> After this initialization procedure, virtual cpu has it's model and
> vendor names, and a working feature set and is ready for identification
> instructions such as CPUID.
>
> Currently full output for this method is only supported for x86 cpus.
>
> To learn exactly how virtual cpu is presented to the guest machine via CPUID
> instruction, new qapi method can be used. By calling 'query-kvm-cpuid'
> method, one can get a full listing of all CPUID leafs with subleafs which are
> supported by the initialized virtual cpu.
>
> Other than debug, the method is useful in cases when we would like to
> utilize QEMU's virtual cpu initialization routines and put the retrieved
> values into kernel CPUID overriding mechanics for more precise control
> over how various processes perceive its underlying hardware with
> container processes as a good example.
>
> Output format:
> The output is a plain list of leaf/subleaf agrument combinations, that
> return 4 words in registers EAX, EBX, ECX, EDX.
>
> Use example:
> qmp_request: {
>    "execute": "query-kvm-cpuid"
> }
>
> qmp_response: {
>    "return": [
>      {
>        "eax": 1073741825,
>        "edx": 77,
>        "in-eax": 1073741824,
>        "ecx": 1447775574,
>        "ebx": 1263359563
>      },
>      {
>        "eax": 16777339,
>        "edx": 0,
>        "in-eax": 1073741825,
>        "ecx": 0,
>        "ebx": 0
>      },
>      {
>        "eax": 13,
>        "edx": 1231384169,
>        "in-eax": 0,
>        "ecx": 1818588270,
>        "ebx": 1970169159
>      },
>      {
>        "eax": 198354,
>        "edx": 126614527,
>        "in-eax": 1,
>        "ecx": 2176328193,
>        "ebx": 2048
>      },
>      ....
>      {
>        "eax": 12328,
>        "edx": 0,
>        "in-eax": 2147483656,
>        "ecx": 0,
>        "ebx": 0
>      }
>    ]
> }
>
> Signed-off-by: Valeriy Vdovin<valeriy.vdovin@virtuozzo.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

--
Best regards,
Vladimir