[PATCH v5 51/51] 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.

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

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/kvm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index f9a6346077b0..beea0b6aa78e 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -990,7 +990,7 @@ 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 timing_info_leaf;
+	u32 timing_info_leaf, apic_khz;
 	bool tsc_is_reliable;
 
 	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) &&
@@ -1052,6 +1052,11 @@ 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;
 		}
+
+		/* The leaf also includes the local APIC bus/timer frequency.*/
+		apic_khz = cpuid_ebx(timing_info_leaf);
+		if (apic_khz)
+			apic_set_timer_period_khz(apic_khz, "KVM hypervisor");
 	}
 
 	/*
-- 
2.55.0.rc0.799.gd6f94ed593-goog