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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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@ -34,6 +34,7 @@ namespace Kernel {
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ProcessorInfo::ProcessorInfo(Processor& processor)
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: m_processor(processor)
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{
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u32 max_leaf;
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{
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CPUID cpuid(0);
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StringBuilder builder;
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@ -44,12 +45,14 @@ ProcessorInfo::ProcessorInfo(Processor& processor)
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(value >> 16) & 0xff,
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(value >> 24) & 0xff);
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};
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max_leaf = cpuid.eax();
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emit_u32(cpuid.ebx());
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emit_u32(cpuid.edx());
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emit_u32(cpuid.ecx());
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m_cpuid = builder.build();
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}
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{
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ASSERT(max_leaf >= 1);
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CPUID cpuid(1);
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m_stepping = cpuid.eax() & 0xf;
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u32 model = (cpuid.eax() >> 4) & 0xf;
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@ -68,9 +71,10 @@ ProcessorInfo::ProcessorInfo(Processor& processor)
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m_display_model = model;
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}
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}
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{
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// FIXME: Check first that this is supported by calling CPUID with eax=0x80000000
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// and verifying that the returned eax>=0x80000004.
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u32 max_extended_leaf = CPUID(0x80000000).eax();
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if (max_extended_leaf >= 0x80000004) {
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alignas(u32) char buffer[48];
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u32* bufptr = reinterpret_cast<u32*>(buffer);
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auto copy_brand_string_part_to_buffer = [&](u32 i) {
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