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KVM: x86: Rate-limit global clock updates on vCPU load

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commit 446fcce2a5 ("Revert "x86: kvm: rate-limit global clock updates"")
dropped the rate limiting for KVM_REQ_GLOBAL_CLOCK_UPDATE.

As a result, kvm_arch_vcpu_load() can queue global clock update requests
every time a vCPU is scheduled when the master clock is disabled or when
the vCPU is loaded for the first time.

Restore the throttling with a per-VM ratelimit state and gate
KVM_REQ_GLOBAL_CLOCK_UPDATE through __ratelimit(), so frequent vCPU
scheduling does not generate a steady stream of redundant clock update
requests.

Fixes: 446fcce2a5 ("Revert "x86: kvm: rate-limit global clock updates"")
Signed-off-by: Lei Chen <lei.chen@smartx.com>
Reported-by: Jaroslav Pulchart <jaroslav.pulchart@gooddata.com>
Closes: https://lore.kernel.org/all/CAK8fFZ5gY8_Mw2A=iZVFNVKQNrXQzVsn-HTd+Me9K6ZfmdgA+Q@mail.gmail.com/
Link: https://patch.msgid.link/20260409142226.2581-1-lei.chen@smartx.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Lei Chen 2026-04-09 22:22:26 +08:00 committed by Sean Christopherson
parent fff82ea9d9
commit 8fe2e698fc
2 changed files with 10 additions and 2 deletions
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1
arch/x86/include/asm/kvm_host.h
View File

@ -1504,6 +1504,7 @@ struct kvm_arch {
bool use_master_clock;
u64 master_kernel_ns;
u64 master_cycle_now;
struct ratelimit_state kvmclock_update_rs;
#ifdef CONFIG_KVM_HYPERV
struct kvm_hv hyperv;

11
arch/x86/kvm/x86.c
View File

@ -5227,8 +5227,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
* On a host with synchronized TSC, there is no need to update
* kvmclock on vcpu->cpu migration
*/
if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) {
if (__ratelimit(&vcpu->kvm->arch.kvmclock_update_rs))
kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
else
kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
}
if (vcpu->cpu != cpu)
kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu);
vcpu->cpu = cpu;
@ -13366,6 +13371,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
raw_spin_lock_init(&kvm->arch.tsc_write_lock);
mutex_init(&kvm->arch.apic_map_lock);
seqcount_raw_spinlock_init(&kvm->arch.pvclock_sc, &kvm->arch.tsc_write_lock);
ratelimit_state_init(&kvm->arch.kvmclock_update_rs, HZ, 10);
ratelimit_set_flags(&kvm->arch.kvmclock_update_rs, RATELIMIT_MSG_ON_RELEASE);
kvm->arch.kvmclock_offset = -get_kvmclock_base_ns();
raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);