Revert "x86: kvm: rate-limit global clock updates"

This reverts commit 7e44e44.

Commit 7e44e44 ("x86: kvm: rate-limit global clock updates")
intends to use a kvmclock_update_work to sync ntp corretion
across all vcpus kvmclock, which is based on commit 0061d53
("KVM: x86: limit difference between kvmclock updates")

Since kvmclock has been switched to mono raw, this commit can be
reverted.

Signed-off-by: Lei Chen <lei.chen@smartx.com>
Link: https://patch.msgid.link/20250819152027.1687487-3-lei.chen@smartx.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Lei Chen

arch/x86/include/asm/kvm_host.h

@@ -1456,7 +1456,6 @@ struct kvm_arch {
 	bool use_master_clock;
 	u64 master_kernel_ns;
 	u64 master_cycle_now;
-	struct delayed_work kvmclock_update_work;
 
 #ifdef CONFIG_KVM_HYPERV
 	struct kvm_hv hyperv;

arch/x86/kvm/x86.c

@@ -3523,38 +3523,21 @@ uint64_t kvm_get_wall_clock_epoch(struct kvm *kvm)
  * the others.
  *
  * So in those cases, request a kvmclock update for all vcpus.
- * We need to rate-limit these requests though, as they can
- * considerably slow guests that have a large number of vcpus.
- * The time for a remote vcpu to update its kvmclock is bound
- * by the delay we use to rate-limit the updates.
+ * The worst case for a remote vcpu to update its kvmclock
+ * is then bounded by maximum nohz sleep latency.
  */
-
-#define KVMCLOCK_UPDATE_DELAY msecs_to_jiffies(100)
-
-static void kvmclock_update_fn(struct work_struct *work)
+static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
 {
 	unsigned long i;
-	struct delayed_work *dwork = to_delayed_work(work);
-	struct kvm_arch *ka = container_of(dwork, struct kvm_arch,
-					   kvmclock_update_work);
-	struct kvm *kvm = container_of(ka, struct kvm, arch);
 	struct kvm_vcpu *vcpu;
+	struct kvm *kvm = v->kvm;
 
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 		kvm_vcpu_kick(vcpu);
 	}
 }
 
-static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
-{
-	struct kvm *kvm = v->kvm;
-
-	kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
-	schedule_delayed_work(&kvm->arch.kvmclock_update_work,
-					KVMCLOCK_UPDATE_DELAY);
-}
-
 /* These helpers are safe iff @msr is known to be an MCx bank MSR. */
 static bool is_mci_control_msr(u32 msr)
 {
@@ -13163,8 +13146,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	kvm->arch.hv_root_tdp = INVALID_PAGE;
 #endif
 
-	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
-
 	kvm_apicv_init(kvm);
 	kvm_hv_init_vm(kvm);
 	kvm_xen_init_vm(kvm);
@@ -13271,8 +13252,6 @@ void kvm_arch_pre_destroy_vm(struct kvm *kvm)
 	 * is unsafe, i.e. will lead to use-after-free.  The PIT also needs to
 	 * be stopped before IRQ routing is freed.
 	 */
-	cancel_delayed_work_sync(&kvm->arch.kvmclock_update_work);
-
 #ifdef CONFIG_KVM_IOAPIC
 	kvm_free_pit(kvm);
 #endif