| Message ID | 20200711100434.46660-3-drjones@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: pvtime: Fixes and a new cap | expand |
On 2020-07-11 11:04, Andrew Jones wrote: > We should only check current->sched_info.run_delay once when > updating stolen time. Otherwise there's a chance there could > be a change between checks that we miss (preemption disabling > comes after vcpu request checks). > > Signed-off-by: Andrew Jones <drjones@redhat.com> > --- > arch/arm64/kvm/pvtime.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/pvtime.c b/arch/arm64/kvm/pvtime.c > index 2b22214909be..db5ef097a166 100644 > --- a/arch/arm64/kvm/pvtime.c > +++ b/arch/arm64/kvm/pvtime.c > @@ -13,6 +13,7 @@ > void kvm_update_stolen_time(struct kvm_vcpu *vcpu) > { > struct kvm *kvm = vcpu->kvm; > + u64 last_steal = vcpu->arch.steal.last_steal; > u64 steal; > __le64 steal_le; > u64 offset; > @@ -24,8 +25,8 @@ void kvm_update_stolen_time(struct kvm_vcpu *vcpu) > > /* Let's do the local bookkeeping */ > steal = vcpu->arch.steal.steal; > - steal += current->sched_info.run_delay - vcpu->arch.steal.last_steal; > vcpu->arch.steal.last_steal = current->sched_info.run_delay; > + steal += vcpu->arch.steal.last_steal - last_steal; > vcpu->arch.steal.steal = steal; > > steal_le = cpu_to_le64(steal); Unless you read current->sched_info.run_delay using READ_ONCE, there is no guarantee that this will do what you want. The compiler is free to rejig this anyway it wants. Thanks, M.
diff --git a/arch/arm64/kvm/pvtime.c b/arch/arm64/kvm/pvtime.c index 2b22214909be..db5ef097a166 100644 --- a/arch/arm64/kvm/pvtime.c +++ b/arch/arm64/kvm/pvtime.c @@ -13,6 +13,7 @@ void kvm_update_stolen_time(struct kvm_vcpu *vcpu) { struct kvm *kvm = vcpu->kvm; + u64 last_steal = vcpu->arch.steal.last_steal; u64 steal; __le64 steal_le; u64 offset; @@ -24,8 +25,8 @@ void kvm_update_stolen_time(struct kvm_vcpu *vcpu) /* Let's do the local bookkeeping */ steal = vcpu->arch.steal.steal; - steal += current->sched_info.run_delay - vcpu->arch.steal.last_steal; vcpu->arch.steal.last_steal = current->sched_info.run_delay; + steal += vcpu->arch.steal.last_steal - last_steal; vcpu->arch.steal.steal = steal; steal_le = cpu_to_le64(steal);
We should only check current->sched_info.run_delay once when updating stolen time. Otherwise there's a chance there could be a change between checks that we miss (preemption disabling comes after vcpu request checks). Signed-off-by: Andrew Jones <drjones@redhat.com> --- arch/arm64/kvm/pvtime.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)