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Kernel: Use FXSR feature only if supported by CPU

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If FXSR is not present, fall back to fnsave and frstor instructions.
These instructions aren't available on the canonical i686 CPU which is
the Pentium Pro processor.
This commit is contained in:
Jean-Baptiste Boric 2021-06-15 00:04:19 +02:00 • committed by Andreas Kling
parent fea23d0ec1
commit fb3447f7ec
1 changed files with 23 additions and 6 deletions
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29
Kernel/Arch/i386/CPU.cpp
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@ -1049,8 +1049,12 @@ UNMAP_AFTER_INIT void Processor::cpu_setup()
// initialized yet!
cpu_detect();
if (has_feature(CPUFeature::SSE))
if (has_feature(CPUFeature::SSE)) {
// enter_thread_context() assumes that if a x86 CPU supports SSE then it also supports FXSR.
// SSE support without FXSR is an extremely unlikely scenario, so let's be pragmatic about it.
VERIFY(has_feature(CPUFeature::FXSR));
sse_init();
}
write_cr0(read_cr0() | 0x00010000);
@ -1233,8 +1237,12 @@ UNMAP_AFTER_INIT void Processor::initialize(u32 cpu)
if (cpu == 0) {
VERIFY((FlatPtr(&s_clean_fpu_state) & 0xF) == 0);
asm volatile("fninit");
asm volatile("fxsave %0"
: "=m"(s_clean_fpu_state));
if (has_feature(CPUFeature::FXSR))
asm volatile("fxsave %0"
: "=m"(s_clean_fpu_state));
else
asm volatile("fnsave %0"
: "=m"(s_clean_fpu_state));
}
m_info = new ProcessorInfo(*this);
@ -1412,12 +1420,18 @@ extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
VERIFY(from_thread == to_thread || from_thread->state() != Thread::Running);
VERIFY(to_thread->state() == Thread::Running);
bool has_fxsr = Processor::current().has_feature(CPUFeature::FXSR);
Processor::set_current_thread(*to_thread);
auto& from_tss = from_thread->tss();
auto& to_tss = to_thread->tss();
asm volatile("fxsave %0"
: "=m"(from_thread->fpu_state()));
if (has_fxsr)
asm volatile("fxsave %0"
: "=m"(from_thread->fpu_state()));
else
asm volatile("fnsave %0"
: "=m"(from_thread->fpu_state()));
from_tss.fs = get_fs();
from_tss.gs = get_gs();
@ -1444,7 +1458,10 @@ extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
to_thread->set_cpu(processor.get_id());
processor.restore_in_critical(to_thread->saved_critical());
asm volatile("fxrstor %0" ::"m"(to_thread->fpu_state()));
if (has_fxsr)
asm volatile("fxrstor %0" ::"m"(to_thread->fpu_state()));
else
asm volatile("frstor %0" ::"m"(to_thread->fpu_state()));
// TODO: ioperm?
}