Mailing List Archive

From: Isaku Yamahata <isaku.yamahata@intel.com>

Remove APIC_BUS_FREQUENCY and calculate it based on nanoseconds per APIC
bus cycle. APIC_BUS_FREQUENCY is used only for HV_X64_MSR_APIC_FREQUENCY.
The MSR is not frequently read, calculate it every time.

There are two constants related to the APIC bus frequency:
APIC_BUS_FREQUENCY and APIC_BUS_CYCLE_NS.
Only one value is required because one can be calculated from the other:
APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.

Remove APIC_BUS_FREQUENCY and instead calculate it when needed.
This prepares for support of configurable APIC bus frequency by
requiring to change only a single variable.

Suggested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Maxim Levitsky <maximlevitsky@gmail.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
[reinette: rework changelog]
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes v5:
- Add Rick's Reviewed-by tag.

Changes v4:
- Modify subject to match custom: "KVM: x86/hyperv:" ->
"KVM: x86: hyper-v:" and use standard capitalization for Hyper-V
("hyper-v" -> "Hyper-V").
- Rework changelog to remove pronouns ("we").
- Change logic in commit log: "APIC bus cycles per NS" -> "nanoseconds
per APIC bus cycle".
- Fix typos. (Maxim and Xiaoyao)
- Add Maxim and Xiaoyao's Reviewed-by tags.
- Add Maxim's "Suggested-by".

Changes v3:
- Newly added according to Maxim Levitsky 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 8a47f8541eab..1030701db967 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1737,7 +1737,7 @@ 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
--
2.34.1