kvmclock updates which are isolated to a given vcpu, such as vcpu->cpu
migration, should not allow system_timestamp from the rest of the vcpus
to remain static. Otherwise ntp frequency correction applies to one
vcpu's system_timestamp but not the others.
So in those cases, request a kvmclock update for all vcpus. The worst
case for a remote vcpu to update its kvmclock is then bounded by maximum
nohz sleep latency.
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 94f35d2..a37cadc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1569,6 +1569,30 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
return 0;
}
+/*
+ * kvmclock updates which are isolated to a given vcpu, such as
+ * vcpu->cpu migration, should not allow system_timestamp from
+ * the rest of the vcpus to remain static. Otherwise ntp frequency
+ * correction applies to one vcpu's system_timestamp but not
+ * the others.
+ *
+ * So in those cases, request a kvmclock update for all vcpus.
+ * The worst case for a remote vcpu to update its kvmclock
+ * is then bounded by maximum nohz sleep latency.
+ */
+
+static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
+{
+ int i;
+ struct kvm *kvm = v->kvm;
+ struct kvm_vcpu *vcpu;
+
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests);
+ kvm_vcpu_kick(vcpu);
+ }
+}
+
static bool msr_mtrr_valid(unsigned msr)
{
switch (msr) {
@@ -1965,7 +1989,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
kvmclock_reset(vcpu);
vcpu->arch.time = data;
- kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+ kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
/* we verify if the enable bit is set... */
if (!(data & 1))
@@ -2684,7 +2708,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
* kvmclock on vcpu->cpu migration
*/
if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
- kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+ kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
if (vcpu->cpu != cpu)
kvm_migrate_timers(vcpu);
vcpu->cpu = cpu;
@@ -5704,6 +5728,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
__kvm_migrate_timers(vcpu);
if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu))
kvm_gen_update_masterclock(vcpu->kvm);
+ if (kvm_check_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu))
+ kvm_gen_kvmclock_update(vcpu);
if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
r = kvm_guest_time_update(vcpu);
if (unlikely(r))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7823b63..044b0b9 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -126,6 +126,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_MCLOCK_INPROGRESS 19
#define KVM_REQ_EPR_EXIT 20
#define KVM_REQ_SCAN_IOAPIC 21
+#define KVM_REQ_GLOBAL_CLOCK_UPDATE 22
#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
--
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