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arch: x86_64: Avoid calling cpuid for setting LAPIC ID

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Rather than calling cpuid and then updating the APIC ID field - use the
existing common CPUID data which already includes CPUID data for eax=1
(aka function = 1).  This removes the need to call cpuid per vCPU thread
created. This has a positive impact on boot time with multiple vCPUs as
the cpuid instruction is serialising.

Fixes: #5646

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
This commit is contained in:
Rob Bradford 2024-05-30 13:39:38 +01:00 committed by Bo Chen
parent d3cd25566b
commit eb4dd90532
1 changed files with 11 additions and 6 deletions
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17
arch/src/x86_64/mod.rs
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@ -820,12 +820,17 @@ pub fn configure_vcpu(
CpuidPatch::set_cpuid_reg(&mut cpuid, 0x8000_001e, Some(0), CpuidReg::EAX, x2apic_id);
}
// Set ApicId in cpuid for each vcpu
// SAFETY: get host cpuid when eax=1
let mut cpu_ebx = unsafe { core::arch::x86_64::__cpuid(1) }.ebx;
cpu_ebx &= 0xffffff;
cpu_ebx |= x2apic_id << 24;
CpuidPatch::set_cpuid_reg(&mut cpuid, 0x1, None, CpuidReg::EBX, cpu_ebx);
// Set ApicId in cpuid for each vcpu - found in cpuid ebx when eax = 1
let mut apic_id_patched = false;
for entry in &mut cpuid {
if entry.function == 1 {
entry.ebx &= 0xffffff;
entry.ebx |= x2apic_id << 24;
apic_id_patched = true;
break;
}
}
assert!(apic_id_patched);
if let Some(t) = topology {
update_cpuid_topology(&mut cpuid, t.0, t.1, t.2, cpu_vendor, id);