[08/10] KVM: x86: Remove periodic global clock updates

Commit Message

David Woodhouse April 18, 2024, 7:34 p.m. UTC

From: David Woodhouse <[e-mail]>

This effectively reverts commit 332967a3eac0 ("x86: kvm: introduce
periodic global clock updates"). The periodic update was introduced to
propagate NTP corrections to the guest KVM clock, when the KVM clock was
based on CLOCK_MONOTONIC.

However, commit 53fafdbb8b21 ("KVM: x86: switch KVMCLOCK base to
monotonic raw clock") switched to using CLOCK_MONOTONIC_RAW as the basis
for the KVM clock, avoiding the NTP frequency skew altogether.

So the periodic update serves no purpose. Remove it.

Signed-off-by: David Woodhouse <[e-mail]>
---
 arch/x86/kvm/x86.c | 25 -------------------------
 1 file changed, 25 deletions(-)

Comments

Paul Durrant April 19, 2024, 3:55 p.m. UTC | #1

On 18/04/2024 20:34, David Woodhouse wrote:
> From: David Woodhouse <[e-mail]>
> 
> This effectively reverts commit 332967a3eac0 ("x86: kvm: introduce
> periodic global clock updates"). The periodic update was introduced to
> propagate NTP corrections to the guest KVM clock, when the KVM clock was
> based on CLOCK_MONOTONIC.
> 
> However, commit 53fafdbb8b21 ("KVM: x86: switch KVMCLOCK base to
> monotonic raw clock") switched to using CLOCK_MONOTONIC_RAW as the basis
> for the KVM clock, avoiding the NTP frequency skew altogether.
> 
> So the periodic update serves no purpose. Remove it.
> 
> Signed-off-by: David Woodhouse <[e-mail]>
> ---
>   arch/x86/kvm/x86.c | 25 -------------------------
>   1 file changed, 25 deletions(-)
> 

Reviewed-by: Paul Durrant <[e-mail]>

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44b3d2a0da5b..4ec4eb850c5b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -155,9 +155,6 @@  EXPORT_SYMBOL_GPL(report_ignored_msrs);
 unsigned int min_timer_period_us = 200;
 module_param(min_timer_period_us, uint, 0644);
 
-static bool __read_mostly kvmclock_periodic_sync = true;
-module_param(kvmclock_periodic_sync, bool, 0444);
-
 /* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */
 static u32 __read_mostly tsc_tolerance_ppm = 250;
 module_param(tsc_tolerance_ppm, uint, 0644);
@@ -3434,20 +3431,6 @@  static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
 					KVMCLOCK_UPDATE_DELAY);
 }
 
-#define KVMCLOCK_SYNC_PERIOD (300 * HZ)
-
-static void kvmclock_sync_fn(struct work_struct *work)
-{
-	struct delayed_work *dwork = to_delayed_work(work);
-	struct kvm_arch *ka = container_of(dwork, struct kvm_arch,
-					   kvmclock_sync_work);
-	struct kvm *kvm = container_of(ka, struct kvm, arch);
-
-	schedule_delayed_work(&kvm->arch.kvmclock_update_work, 0);
-	schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
-					KVMCLOCK_SYNC_PERIOD);
-}
-
 /* These helpers are safe iff @msr is known to be an MCx bank MSR. */
 static bool is_mci_control_msr(u32 msr)
 {
@@ -12416,8 +12399,6 @@  int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 {
-	struct kvm *kvm = vcpu->kvm;
-
 	if (mutex_lock_killable(&vcpu->mutex))
 		return;
 	vcpu_load(vcpu);
@@ -12428,10 +12409,6 @@  void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	vcpu->arch.msr_kvm_poll_control = 1;
 
 	mutex_unlock(&vcpu->mutex);
-
-	if (kvmclock_periodic_sync && vcpu->vcpu_idx == 0)
-		schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
-						KVMCLOCK_SYNC_PERIOD);
 }
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
@@ -12804,7 +12781,6 @@  int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 #endif
 
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
-	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
 
 	kvm_apicv_init(kvm);
 	kvm_hv_init_vm(kvm);
@@ -12844,7 +12820,6 @@  static void kvm_unload_vcpu_mmus(struct kvm *kvm)
 
 void kvm_arch_sync_events(struct kvm *kvm)
 {
-	cancel_delayed_work_sync(&kvm->arch.kvmclock_sync_work);
 	cancel_delayed_work_sync(&kvm->arch.kvmclock_update_work);
 	kvm_free_pit(kvm);
 }