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kernel/x86: Clean up AMD C1E feature detection.

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* If the CPUID bit is present, don't bother checking the models.
   (This will happen on hypervisors.)

 * Set the CPUID bit if we determine it's present.

 * Only do this on CPU 0.
This commit is contained in:
Augustin Cavalier
2025-08-22 15:04:34 -04:00
parent d3627801d7
commit 65daa8c146
1 changed files with 14 additions and 6 deletions
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src/system/kernel/arch/x86/arch_cpu.cpp
+14 -6
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@@ -1605,12 +1605,21 @@ detect_amdc1e_noarat()
if (cpu->arch.vendor != VENDOR_AMD)
return false;
// Family 0x12 and higher processors support ARAT
// Family lower than 0xf processors doesn't support C1E
// Family 0xf with model <= 0x40 procssors doesn't support C1E
if (cpu->arch.feature[FEATURE_6_EAX] & IA32_FEATURE_ARAT)
return false;
uint32 family = cpu->arch.family + cpu->arch.extended_family;
uint32 model = (cpu->arch.extended_model << 4) | cpu->arch.model;
return (family < 0x12 && family > 0xf) || (family == 0xf && model > 0x40);
if (family >= 0x12) {
// Family 0x12 and higher processors support ARAT correctly,
// but they don't declare it in the CPUID until 0x17 (Zen).
cpu->arch.feature[FEATURE_6_EAX] |= IA32_FEATURE_ARAT;
return false;
}
// Family lower than 0xf processors doesn't support C1E
// Family 0xf with model <= 0x40 processors doesn't support C1E
return (family > 0xf) || (family == 0xf && model > 0x40);
}
@@ -1732,10 +1741,9 @@ arch_cpu_init_percpu(kernel_args* args, int cpu)
load_microcode(cpu);
detect_cpu(cpu);
if (cpu == 0)
if (cpu == 0) {
init_tsc(args);
if (!gCpuIdleFunc) {
if (detect_amdc1e_noarat())
gCpuIdleFunc = amdc1e_noarat_idle;
else