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i386: Reorganize and document CPUID initialization steps

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CPU runnability checks and CPU model expansion have slightly
different requirements. Document the steps involved in loading a
CPU model and realizing a CPU, so their requirements and purpose
are clearly defined.

This patch doesn't change any implementation. It just add
comments, rename the x86_cpu_load_features() function for clarity
(so it won't be confused with x86_cpu_load_def()), and move
x86_cpu_filter_features() closer to it.

Backports commit b8d834a00fa3ed4dad7d371e1a00938a126a54a0 from qemu
This commit is contained in:
Eduardo Habkost 2018-03-02 10:53:43 -05:00 committed by Lioncash
parent be606acff9
commit 33ab5f71c9
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 68 additions and 27 deletions
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95
qemu/target/i386/cpu.c
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@ -2219,30 +2219,6 @@ static uint32_t x86_cpu_get_supported_feature_word(struct uc_struct *uc,
return r;
}
/*
* Filters CPU feature words based on host availability of each feature.
*
* Returns: 0 if all flags are supported by the host, non-zero otherwise.
*/
static int x86_cpu_filter_features(X86CPU *cpu)
{
CPUX86State *env = &cpu->env;
FeatureWord w;
int rv = 0;
for (w = 0; w < FEATURE_WORDS; w++) {
uint32_t host_feat = x86_cpu_get_supported_feature_word(env->uc, w, false);
uint32_t requested_features = env->features[w];
env->features[w] &= host_feat;
cpu->filtered_features[w] = requested_features & ~env->features[w];
if (cpu->filtered_features[w]) {
rv = 1;
}
}
return rv;
}
static void x86_cpu_report_filtered_features(X86CPU *cpu)
{
FeatureWord w;
@ -3069,8 +3045,47 @@ static void x86_cpu_enable_xsave_components(X86CPU *cpu)
env->features[FEAT_XSAVE_COMP_HI] = mask >> 32;
}
/* Load CPUID data based on configured features */
static void x86_cpu_load_features(struct uc_struct *uc, X86CPU *cpu, Error **errp)
/***** Steps involved on loading and filtering CPUID data
*
* When initializing and realizing a CPU object, the steps
* involved in setting up CPUID data are:
*
* 1) Loading CPU model definition (X86CPUDefinition). This is
* implemented by x86_cpu_load_def() and should be completely
* transparent, as it is done automatically by instance_init.
* No code should need to look at X86CPUDefinition structs
* outside instance_init.
*
* 2) CPU expansion. This is done by realize before CPUID
* filtering, and will make sure host/accelerator data is
* loaded for CPU models that depend on host capabilities
* (e.g. "host"). Done by x86_cpu_expand_features().
*
* 3) CPUID filtering. This initializes extra data related to
* CPUID, and checks if the host supports all capabilities
* required by the CPU. Runnability of a CPU model is
* determined at this step. Done by x86_cpu_filter_features().
*
* Some operations don't require all steps to be performed.
* More precisely:
*
* - CPU instance creation (instance_init) will run only CPU
* model loading. CPU expansion can't run at instance_init-time
* because host/accelerator data may be not available yet.
* - CPU realization will perform both CPU model expansion and CPUID
* filtering, and return an error in case one of them fails.
* - query-cpu-definitions needs to run all 3 steps. It needs
* to run CPUID filtering, as the 'unavailable-features'
* field is set based on the filtering results.
* - The query-cpu-model-expansion QMP command only needs to run
* CPU model loading and CPU expansion. It should not filter
* any CPUID data based on host capabilities.
*/
/* Expand CPU configuration data, based on configured features
* and host/accelerator capabilities when appropriate.
*/
static void x86_cpu_expand_features(struct uc_struct *uc, X86CPU *cpu, Error **errp)
{
CPUX86State *env = &cpu->env;
FeatureWord w;
@ -3135,6 +3150,32 @@ static void x86_cpu_load_features(struct uc_struct *uc, X86CPU *cpu, Error **err
}
}
/*
* Finishes initialization of CPUID data, filters CPU feature
* words based on host availability of each feature.
*
* Returns: 0 if all flags are supported by the host, non-zero otherwise.
*/
static int x86_cpu_filter_features(X86CPU *cpu)
{
CPUX86State *env = &cpu->env;
FeatureWord w;
int rv = 0;
for (w = 0; w < FEATURE_WORDS; w++) {
uint32_t host_feat =
x86_cpu_get_supported_feature_word(env->uc, w, false);
uint32_t requested_features = env->features[w];
env->features[w] &= host_feat;
cpu->filtered_features[w] = requested_features & ~env->features[w];
if (cpu->filtered_features[w]) {
rv = 1;
}
}
return rv;
}
#define IS_INTEL_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_INTEL_1 && \
(env)->cpuid_vendor2 == CPUID_VENDOR_INTEL_2 && \
(env)->cpuid_vendor3 == CPUID_VENDOR_INTEL_3)
@ -3163,7 +3204,7 @@ static int x86_cpu_realizefn(struct uc_struct *uc, DeviceState *dev, Error **err
return -1;
}
x86_cpu_load_features(uc, cpu, &local_err);
x86_cpu_expand_features(uc, cpu, &local_err);
if (local_err) {
goto out;
}