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Kernel: Add some CPU feature flags related to TSC
In case we want to rely more on TSC in time keeping in the future, idk This adds: - RDTSCP, for when the RDTSCP instruction is available - CONSTANT_TSC, for when the TSC has a constant frequency, invariant under things like the CPU boosting its frequency. - NONSTOP_TSC, for when the TSC doesn't pause when the CPU enters sleep states. AMD cpus and newer intel cpus set the INVSTC bit (bit 8 in edx of extended cpuid 0x8000000008), which implies both CONSTANT_TSC and NONSTOP_TSC. Some older intel processors have CONSTANT_TSC but not NONSTOP_TSC; this is set based on cpu model checks. There isn't a ton of documentation on this, so this follows Linux terminology and http://blog.tinola.com/?e=54 CONSTANT_TSC:39b3a79105
NONSTOP_TSC:40fb17152c
qemu disables invtsc (bit 8 in edx of extended cpuid 0x8000000008) by default even if the host cpu supports it. It can be enabled by running with `SERENITY_QEMU_CPU=host,migratable=off` set.
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3 changed files with 41 additions and 12 deletions
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@ -998,15 +998,31 @@ void Processor::cpu_detect()
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u32 family = (processor_info.eax() >> 8) & 0xf;
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if (!(family == 6 && model < 3 && stepping < 3))
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set_feature(CPUFeature::SEP);
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if ((family == 6 && model >= 3) || (family == 0xf && model >= 0xe))
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set_feature(CPUFeature::CONSTANT_TSC);
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}
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u32 max_extended_leaf = CPUID(0x80000000).eax();
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ASSERT(max_extended_leaf >= 0x80000001);
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CPUID extended_processor_info(0x80000001);
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if (extended_processor_info.edx() & (1 << 20))
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set_feature(CPUFeature::NX);
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if (extended_processor_info.edx() & (1 << 27))
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set_feature(CPUFeature::RDTSCP);
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if (extended_processor_info.edx() & (1 << 11)) {
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// Only available in 64 bit mode
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set_feature(CPUFeature::SYSCALL);
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}
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if (max_extended_leaf >= 0x80000007) {
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CPUID cpuid(0x80000007);
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if (cpuid.edx() & (1 << 8)) {
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set_feature(CPUFeature::CONSTANT_TSC);
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set_feature(CPUFeature::NONSTOP_TSC);
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}
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}
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CPUID extended_features(0x7);
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if (extended_features.ebx() & (1 << 20))
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set_feature(CPUFeature::SMAP);
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@ -1107,6 +1123,12 @@ String Processor::features_string() const
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return "sse";
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case CPUFeature::TSC:
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return "tsc";
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case CPUFeature::RDTSCP:
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return "rdtscp";
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case CPUFeature::CONSTANT_TSC:
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return "constant_tsc";
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case CPUFeature::NONSTOP_TSC:
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return "nonstop_tsc";
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case CPUFeature::UMIP:
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return "umip";
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case CPUFeature::SEP:
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