diff mbox series

[V4,1/4] KVM: x86: hyper-v: Calculate APIC bus frequency for Hyper-V

Message ID d815921fff4c616c8b05bff0fb9377a171c8633b.1711035400.git.reinette.chatre@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: Make bus clock frequency for vAPIC timer configurable | expand

Commit Message

Reinette Chatre March 21, 2024, 4:37 p.m. UTC 
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>
[reinette: rework changelog]
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---

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(-)

Comments

Edgecombe, Rick P April 16, 2024, 5:07 p.m. UTC | #1 
On Thu, 2024-03-21 at 09:37 -0700, Reinette Chatre wrote:
> 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>
> [reinette: rework changelog]
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
diff mbox series

Patch

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