[PATCH v15] qapi: introduce 'query-x86-cpuid' QMP command.

[PATCH v15] qapi: introduce 'query-x86-cpuid' QMP command.

[Valeriy Vdovin]

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": "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>
---
v2: - Removed leaf/subleaf iterators.
    - Modified cpu_x86_cpuid to return false in cases when count is
      greater than supported subleaves.
v3: - Fixed structure name coding style.
    - Added more comments
    - Ensured buildability for non-x86 targets.
v4: - Fixed cpu_x86_cpuid return value logic and handling of 0xA leaf.
    - Fixed comments.
    - Removed target check in qmp_query_cpu_model_cpuid.
v5: - Added error handling code in qmp_query_cpu_model_cpuid
v6: - Fixed error handling code. Added method to query_error_class
v7: - Changed implementation in favor of cached cpuid_data for
      KVM_SET_CPUID2
v8: - Renamed qmp method to query-kvm-cpuid and some fields in response.
    - Modified documentation to qmp method
    - Removed helper struct declaration
v9: - Renamed 'in_eax' / 'in_ecx' fields to 'in-eax' / 'in-ecx'
    - Pasted more complete response to commit message.
v10:
    - Subject changed
    - Fixes in commit message
    - Small fixes in QMP command docs
v11:
    - Added explanation about CONFIG_KVM to the commit message.
v12:
    - Changed title from query-kvm-cpuid to query-x86-cpuid
    - Removed CONFIG_KVM ifdefs
    - Added detailed error messages for some stub/unimplemented cases.
v13:
    - Tagged with since 6.2
v14:
    - Rebased to latest master 632eda54043d6f26ff87dac16233e14b4708b967
    - Added note about error return cases in api documentation.
v15:
    - Rearranged nested if statements.
    - Made use of kvm_enabled() instead of custom function.
    - Removed generated typedefs
    - Added indentation to qapi docementation.

 qapi/machine-target.json   | 46 ++++++++++++++++++++++++++++++++++++++
 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, 101 insertions(+), 1 deletion(-)

diff --git a/qapi/machine-target.json b/qapi/machine-target.json
index e7811654b7..75398bc1a4 100644
--- a/qapi/machine-target.json
+++ b/qapi/machine-target.json
@@ -329,3 +329,49 @@
 ##
 { 'command': 'query-cpu-definitions', 'returns': ['CpuDefinitionInfo'],
   'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_I386) || defined(TARGET_S390X) || defined(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: 6.2
+##
+{ 'struct': 'CpuidEntry',
+  'data': { 'in-eax' : 'uint32',
+            '*in-ecx' : 'uint32',
+            'eax' : 'uint32',
+            'ebx' : 'uint32',
+            'ecx' : 'uint32',
+            'edx' : 'uint32'
+          },
+  'if': 'defined(TARGET_I386)' }
+
+##
+# @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.
+#
+#
+# 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: 6.2
+##
+{ 'command': 'query-x86-cpuid',
+  'returns': ['CpuidEntry'],
+  'if': 'defined(TARGET_I386)' }
diff --git a/softmmu/cpus.c b/softmmu/cpus.c
index 071085f840..8501081897 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..feb0d7664d 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_query_x86_cpuid(Error **errp);
+
+CpuidEntryList *qmp_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 e69abe48e3..d69d46c5c6 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"
@@ -1540,6 +1542,44 @@ static Error *invtsc_mig_blocker;
 
 #define KVM_MAX_CPUID_ENTRIES  100
 
+struct kvm_cpuid2 *cpuid_data_cached;
+
+
+CpuidEntryList *qmp_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 {
@@ -1923,6 +1963,10 @@ 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 c98b78d033..bd883f7f52 100644
--- a/tests/qtest/qmp-cmd-test.c
+++ b/tests/qtest/qmp-cmd-test.c
@@ -46,6 +46,7 @@ static int query_error_class(const char *cmd)
         { "query-balloon", ERROR_CLASS_DEVICE_NOT_ACTIVE },
         { "query-hotpluggable-cpus", ERROR_CLASS_GENERIC_ERROR },
         { "query-vm-generation-id", ERROR_CLASS_GENERIC_ERROR },
+        { "query-x86-cpuid", ERROR_CLASS_GENERIC_ERROR },
         { NULL, -1 }
     };
     int i;
-- 
2.17.1

Re: [PATCH v15] qapi: introduce 'query-x86-cpuid' QMP command.

[Vladimir Sementsov-Ogievskiy]

Ping.

Hi! Any chance for this to land?

The solution is very simple now: we don't modify any logic and just export kvm_cpuid2 entries as simple and flat QAPI list. What's the problem with it?

If any doubts, we can go with x- prefix for a new command.

16.08.2021 17:51, Valeriy Vdovin 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": "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>
> ---
> v2: - Removed leaf/subleaf iterators.
>      - Modified cpu_x86_cpuid to return false in cases when count is
>        greater than supported subleaves.
> v3: - Fixed structure name coding style.
>      - Added more comments
>      - Ensured buildability for non-x86 targets.
> v4: - Fixed cpu_x86_cpuid return value logic and handling of 0xA leaf.
>      - Fixed comments.
>      - Removed target check in qmp_query_cpu_model_cpuid.
> v5: - Added error handling code in qmp_query_cpu_model_cpuid
> v6: - Fixed error handling code. Added method to query_error_class
> v7: - Changed implementation in favor of cached cpuid_data for
>        KVM_SET_CPUID2
> v8: - Renamed qmp method to query-kvm-cpuid and some fields in response.
>      - Modified documentation to qmp method
>      - Removed helper struct declaration
> v9: - Renamed 'in_eax' / 'in_ecx' fields to 'in-eax' / 'in-ecx'
>      - Pasted more complete response to commit message.
> v10:
>      - Subject changed
>      - Fixes in commit message
>      - Small fixes in QMP command docs
> v11:
>      - Added explanation about CONFIG_KVM to the commit message.
> v12:
>      - Changed title from query-kvm-cpuid to query-x86-cpuid
>      - Removed CONFIG_KVM ifdefs
>      - Added detailed error messages for some stub/unimplemented cases.
> v13:
>      - Tagged with since 6.2
> v14:
>      - Rebased to latest master 632eda54043d6f26ff87dac16233e14b4708b967
>      - Added note about error return cases in api documentation.
> v15:
>      - Rearranged nested if statements.
>      - Made use of kvm_enabled() instead of custom function.
>      - Removed generated typedefs
>      - Added indentation to qapi docementation.
> 
>   qapi/machine-target.json   | 46 ++++++++++++++++++++++++++++++++++++++
>   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, 101 insertions(+), 1 deletion(-)
> 
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index e7811654b7..75398bc1a4 100644
> --- a/qapi/machine-target.json
> +++ b/qapi/machine-target.json
> @@ -329,3 +329,49 @@
>   ##
>   { 'command': 'query-cpu-definitions', 'returns': ['CpuDefinitionInfo'],
>     'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_I386) || defined(TARGET_S390X) || defined(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: 6.2
> +##
> +{ 'struct': 'CpuidEntry',
> +  'data': { 'in-eax' : 'uint32',
> +            '*in-ecx' : 'uint32',
> +            'eax' : 'uint32',
> +            'ebx' : 'uint32',
> +            'ecx' : 'uint32',
> +            'edx' : 'uint32'
> +          },
> +  'if': 'defined(TARGET_I386)' }
> +
> +##
> +# @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.
> +#
> +#
> +# 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: 6.2
> +##
> +{ 'command': 'query-x86-cpuid',
> +  'returns': ['CpuidEntry'],
> +  'if': 'defined(TARGET_I386)' }
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index 071085f840..8501081897 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..feb0d7664d 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_query_x86_cpuid(Error **errp);
> +
> +CpuidEntryList *qmp_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 e69abe48e3..d69d46c5c6 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"
> @@ -1540,6 +1542,44 @@ static Error *invtsc_mig_blocker;
>   
>   #define KVM_MAX_CPUID_ENTRIES  100
>   
> +struct kvm_cpuid2 *cpuid_data_cached;
> +
> +
> +CpuidEntryList *qmp_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 {
> @@ -1923,6 +1963,10 @@ 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 c98b78d033..bd883f7f52 100644
> --- a/tests/qtest/qmp-cmd-test.c
> +++ b/tests/qtest/qmp-cmd-test.c
> @@ -46,6 +46,7 @@ static int query_error_class(const char *cmd)
>           { "query-balloon", ERROR_CLASS_DEVICE_NOT_ACTIVE },
>           { "query-hotpluggable-cpus", ERROR_CLASS_GENERIC_ERROR },
>           { "query-vm-generation-id", ERROR_CLASS_GENERIC_ERROR },
> +        { "query-x86-cpuid", ERROR_CLASS_GENERIC_ERROR },
>           { NULL, -1 }
>       };
>       int i;
> 


-- 
Best regards,
Vladimir

Re: [PATCH v15] qapi: introduce 'query-x86-cpuid' QMP command.

[Thomas Huth]

On 22/09/2021 09.41, Vladimir Sementsov-Ogievskiy wrote:
> Ping.
> 
> Hi! Any chance for this to land?

Sorry if I missed the outcome of the discussion - but what about the idea to 
introduce this with a "x-" prefix first, since there was no 100% certainty 
that we really fully want to support this command in the current fashion?

  Thomas