linux-kernel - [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for hyper-v

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Message-Id: <ecd345619fdddfe48f375160c90322754cec9096.1702974319.git.isaku.yamahata@intel.com>
Date: Tue, 19 Dec 2023 00:34:38 -0800
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Vishal Annapurve <vannapurve@...gle.com>,
	Jim Mattson <jmattson@...gle.com>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	Xiaoyao Li <xiaoyao.li@...el.com>
Cc: isaku.yamahata@...el.com,
	isaku.yamahata@...il.com
Subject: [PATCH v3 1/4] KVM: x86/hyperv: Calculate APIC bus frequency for hyper-v

Remove APIC_BUS_FREUQNCY and calculate it based on APIC bus cycles per NS.
APIC_BUS_FREUQNCY is used only for HV_X64_MSR_APIC_FREQUENCY.  The MSR is
not frequently read, calculate it every time.

In order to make APIC bus frequency configurable, we need to make make two
related constants into variables.  APIC_BUS_FREUQNCY and APIC_BUS_CYCLE_NS.
One can be calculated from the other.
   APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.
By removing APIC_BUS_FREQUENCY, we need to track only single variable
instead of two.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
Changes v3:
- Newly added according to Maxim Levistsky suggestion.
---
 arch/x86/kvm/hyperv.c | 2 +-
 arch/x86/kvm/lapic.h  | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 238afd7335e4..a40ca2fef58c 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1687,7 +1687,7 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
 		data = (u64)vcpu->arch.virtual_tsc_khz * 1000;
 		break;
 	case HV_X64_MSR_APIC_FREQUENCY:
-		data = APIC_BUS_FREQUENCY;
+		data = div64_u64(1000000000ULL, APIC_BUS_CYCLE_NS);
 		break;
 	default:
 		kvm_pr_unimpl_rdmsr(vcpu, msr);
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 0a0ea4b5dd8c..a20cb006b6c8 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -17,7 +17,6 @@
 #define APIC_DEST_MASK			0x800
 
 #define APIC_BUS_CYCLE_NS       1
-#define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
 
 #define APIC_BROADCAST			0xFF
 #define X2APIC_BROADCAST		0xFFFFFFFFul
-- 
2.25.1