On Tue, Aug 10, 2021 at 09:51:31AM +0300, Valeriy Vdovin wrote:
> From: Valeriy Vdovin <valeriy.vdovin@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
> 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.
>
> qapi/machine-target.json | 46 ++++++++++++++++++++++++++++++++++
> softmmu/cpus.c | 2 +-
> target/i386/kvm/kvm-stub.c | 10 ++++++++
> target/i386/kvm/kvm.c | 51 ++++++++++++++++++++++++++++++++++++++
> tests/qtest/qmp-cmd-test.c | 1 +
> 5 files changed, 109 insertions(+), 1 deletion(-)
>
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index e7811654b7..71648a4f56 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..9eb04d908f 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 +45,12 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
> {
> abort();
> }
> +
> +typedef struct CpuidEntryList CpuidEntryList;
> +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..28e79cd0cf 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 +1542,51 @@ static Error *invtsc_mig_blocker;
>
> #define KVM_MAX_CPUID_ENTRIES 100
>
> +struct kvm_cpuid2 *cpuid_data_cached;
> +extern const AccelOpsClass *cpus_accel;
> +
> +static inline int is_kvm_accel(AccelOpsClass *class)
> +{
> + ObjectClass *parent_class;
We normally call ObjectClass variables 'oc'.
> +
> + parent_class = &class->parent_class;
The right way to cast a class/object to a different type is to
use the type casting macros. e.g.:
oc = OBJECT_CLASS(class);
> + return strcmp(object_class_get_name(parent_class),
> + "kvm-accel-ops") == 0;
You should never do a string comparison of the QOM type name to
decide what to do. If you want to know if a class implements a
specific type, you can just call:
object_class_dynamic_cast(class, TYPE_KVM_ACCEL)
In either case, this function can probably be deleted and
replaced with a simple kvm_enabled() call (see below).
> +}
> +
> +CpuidEntryList *qmp_query_x86_cpuid(Error **errp)
> +{
> + int i;
> + struct kvm_cpuid_entry2 *kvm_entry;
> + CpuidEntryList *head = NULL, **tail = &head;
> + CpuidEntry *entry;
> +
> + if (!cpuid_data_cached) {
> + if (cpus_accel && !is_kvm_accel((AccelOpsClass *)cpus_accel))
This can be replaced by a kvm_enabled() check.
Also, I suggest avoid nesting conditionals when possible. e.g.:
if (!kvm_enabled()) {
error_setg(...);
return NULL;
}
if (!cpuid_data_cached) {
error_setg(...);
return NULL;
}
> + error_setg(errp, "Not implemented for non-kvm accel");
> + else
> + 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 +1970,10 @@ 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
>
--
Eduardo
