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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.
This commit is contained in:
Nico Weber 2020-10-07 13:19:09 -04:00 committed by Andreas Kling
parent 1d96d5eea4
commit 8a01be4849
3 changed files with 41 additions and 12 deletions

View file

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