Re: [PATCH v17] qapi: introduce 'x-query-x86-cpuid' QMP command.

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Ping :) Any hope that we will merge it one day?)

21.01.2022 19:39, Vladimir Sementsov-Ogievskiy wrote:
> From: Valeriy Vdovin <valeriy.vdovin@virtuozzo.com>
> 
> Introducing new QMP command 'query-x86-cpuid'. This command 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.
> 
> To learn exactly how virtual CPU is presented to the guest machine via
> CPUID instruction, new QMP command can be used. By calling
> 'query-x86-cpuid' command, one can get a full listing of all CPUID
> leaves with subleaves which are supported by the initialized virtual
> CPU.
> 
> Other than debug, the command 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.
> 
> The command is specific to x86. It is currenly only implemented for
> KVM acceleator.
> 
> Output format:
> The output is a plain list of leaf/subleaf argument combinations, that
> return 4 words in registers EAX, EBX, ECX, EDX.
> 
> Use example:
> qmp_request: {
>    "execute": "x-query-x86-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>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> v17: wrap long lines, add QAPI feature 'unstable' [Markus]
> 
>   qapi/machine-target.json   | 50 ++++++++++++++++++++++++++++++++++++++
>   softmmu/cpus.c             |  2 +-
>   target/i386/kvm/kvm-stub.c |  9 +++++++
>   target/i386/kvm/kvm.c      | 44 +++++++++++++++++++++++++++++++++
>   tests/qtest/qmp-cmd-test.c |  1 +
>   5 files changed, 105 insertions(+), 1 deletion(-)
> 
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index f5ec4bc172..1568e17e74 100644
> --- a/qapi/machine-target.json
> +++ b/qapi/machine-target.json
> @@ -341,3 +341,53 @@
>                      'TARGET_I386',
>                      'TARGET_S390X',
>                      'TARGET_MIPS' ] } }
> +
> +##
> +# @CpuidEntry:
> +#
> +# A single entry of a CPUID response.
> +#
> +# One entry holds full set of information (leaf) returned to the guest
> +# in response to it calling a CPUID instruction with eax, ecx used as
> +# the arguments to that instruction. ecx is an optional argument as
> +# not all of the leaves support it.
> +#
> +# @in-eax: CPUID argument in eax
> +# @in-ecx: CPUID argument in ecx
> +# @eax: CPUID result in eax
> +# @ebx: CPUID result in ebx
> +# @ecx: CPUID result in ecx
> +# @edx: CPUID result in edx
> +#
> +# Since: 7.0
> +##
> +{ 'struct': 'CpuidEntry',
> +  'data': { 'in-eax' : 'uint32',
> +            '*in-ecx' : 'uint32',
> +            'eax' : 'uint32',
> +            'ebx' : 'uint32',
> +            'ecx' : 'uint32',
> +            'edx' : 'uint32'
> +          },
> +  'if': 'TARGET_I386' }
> +
> +##
> +# @x-query-x86-cpuid:
> +#
> +# Returns raw data from the emulated CPUID table for the first VCPU.
> +# The emulated CPUID table defines the response to the CPUID
> +# instruction when executed by the guest operating system.
> +#
> +# Features:
> +# @unstable: This command is experimental.
> +#
> +# Returns: a list of CpuidEntry. Returns error when qemu is configured
> +#          with --disable-kvm flag or if qemu is run with any other
> +#          accelerator than KVM.
> +#
> +# Since: 7.0
> +##
> +{ 'command': 'x-query-x86-cpuid',
> +  'returns': [ 'CpuidEntry' ],
> +  'if': 'TARGET_I386',
> +  'features': [ 'unstable' ] }
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index 23bca46b07..33045bf45c 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -129,7 +129,7 @@ void hw_error(const char *fmt, ...)
>   /*
>    * The chosen accelerator is supposed to register this.
>    */
> -static const AccelOpsClass *cpus_accel;
> +const AccelOpsClass *cpus_accel;
>   
>   void cpu_synchronize_all_states(void)
>   {
> diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
> index f6e7e4466e..71631e560d 100644
> --- a/target/i386/kvm/kvm-stub.c
> +++ b/target/i386/kvm/kvm-stub.c
> @@ -12,6 +12,7 @@
>   #include "qemu/osdep.h"
>   #include "cpu.h"
>   #include "kvm_i386.h"
> +#include "qapi/error.h"
>   
>   #ifndef __OPTIMIZE__
>   bool kvm_has_smm(void)
> @@ -44,3 +45,11 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>   {
>       abort();
>   }
> +
> +CpuidEntryList *qmp_x_query_x86_cpuid(Error **errp);
> +
> +CpuidEntryList *qmp_x_query_x86_cpuid(Error **errp)
> +{
> +    error_setg(errp, "Not implemented in --disable-kvm configuration");
> +    return NULL;
> +}
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 2c8feb4a6f..eb73869039 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -20,11 +20,13 @@
>   
>   #include <linux/kvm.h>
>   #include "standard-headers/asm-x86/kvm_para.h"
> +#include "qapi/qapi-commands-machine-target.h"
>   
>   #include "cpu.h"
>   #include "host-cpu.h"
>   #include "sysemu/sysemu.h"
>   #include "sysemu/hw_accel.h"
> +#include "sysemu/accel-ops.h"
>   #include "sysemu/kvm_int.h"
>   #include "sysemu/runstate.h"
>   #include "kvm_i386.h"
> @@ -1565,6 +1567,44 @@ static Error *invtsc_mig_blocker;
>   
>   #define KVM_MAX_CPUID_ENTRIES  100
>   
> +struct kvm_cpuid2 *cpuid_data_cached;
> +
> +
> +CpuidEntryList *qmp_x_query_x86_cpuid(Error **errp)
> +{
> +    int i;
> +    struct kvm_cpuid_entry2 *kvm_entry;
> +    CpuidEntryList *head = NULL, **tail = &head;
> +    CpuidEntry *entry;
> +
> +    if (!kvm_enabled()) {
> +        error_setg(errp, "Not implemented for non-kvm accel");
> +        return NULL;
> +    }
> +
> +    if (!cpuid_data_cached) {
> +        error_setg(errp, "VCPU was not initialized yet");
> +        return NULL;
> +    }
> +
> +    for (i = 0; i < cpuid_data_cached->nent; ++i) {
> +        kvm_entry = &cpuid_data_cached->entries[i];
> +        entry = g_malloc0(sizeof(*entry));
> +        entry->in_eax = kvm_entry->function;
> +        if (kvm_entry->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) {
> +            entry->in_ecx = kvm_entry->index;
> +            entry->has_in_ecx = true;
> +        }
> +        entry->eax = kvm_entry->eax;
> +        entry->ebx = kvm_entry->ebx;
> +        entry->ecx = kvm_entry->ecx;
> +        entry->edx = kvm_entry->edx;
> +        QAPI_LIST_APPEND(tail, entry);
> +    }
> +
> +    return head;
> +}
> +
>   int kvm_arch_init_vcpu(CPUState *cs)
>   {
>       struct {
> @@ -1981,6 +2021,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>       if (r) {
>           goto fail;
>       }
> +    if (!cpuid_data_cached) {
> +        cpuid_data_cached = g_malloc0(sizeof(cpuid_data));
> +        memcpy(cpuid_data_cached, &cpuid_data, sizeof(cpuid_data));
> +    }
>   
>       if (has_xsave) {
>           env->xsave_buf_len = sizeof(struct kvm_xsave);
> diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
> index 7f103ea3fd..94d9184a84 100644
> --- a/tests/qtest/qmp-cmd-test.c
> +++ b/tests/qtest/qmp-cmd-test.c
> @@ -54,6 +54,7 @@ static int query_error_class(const char *cmd)
>           /* Only valid with accel=tcg */
>           { "x-query-jit", ERROR_CLASS_GENERIC_ERROR },
>           { "x-query-opcount", ERROR_CLASS_GENERIC_ERROR },
> +        { "x-query-x86-cpuid", ERROR_CLASS_GENERIC_ERROR },
>           { NULL, -1 }
>       };
>       int i;
> 


-- 
Best regards,
Vladimir