[PATCH v4 18/47] x86/kvm: Get local APIC bus frequency from PV CPUID Timing Info

[Sean Christopherson]

When running as a KVM guest with PV timing info provided by the host,
stuff the APIC timer period/frequency with the local APIC bus frequency
reported in CPUID.0x40000010.EBX instead of trying to calibrate/guess the
frequency.

Note, the unit of measurement for lapic_timer_period is "ticks per HZ", not
Khz.

See Documentation/virt/kvm/x86/cpuid.rst for details.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/kvm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 4fe9c69bf40b..c1139182121d 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -977,6 +977,7 @@ static void __init kvm_init_platform(void)
 		.mask_lo = (u32)(~(SZ_4G - tolud - 1)) | MTRR_PHYSMASK_V,
 		.mask_hi = (BIT_ULL(boot_cpu_data.x86_phys_bits) - 1) >> 32,
 	};
+	u32 apic_khz __maybe_unused;
 	u32 timing_info_leaf;
 	bool tsc_is_reliable;
 
@@ -1039,6 +1040,13 @@ static void __init kvm_init_platform(void)
 			x86_init.hyper.get_tsc_khz = kvm_get_tsc_khz;
 			x86_init.hyper.get_cpu_khz = kvm_get_tsc_khz;
 		}
+
+#ifdef CONFIG_X86_LOCAL_APIC
+		/* The leaf also includes the local APIC bus/timer frequency.*/
+		apic_khz = cpuid_ebx(timing_info_leaf);
+		if (apic_khz)
+	               lapic_timer_period = apic_khz * 1000 / HZ;
+#endif
 	}
 
         /*
-- 
2.54.0.823.g6e5bcc1fc9-goog