KVM: PPC: Book3S HV: Report stolen time to guest through dispatch trace log

This adds code to measure "stolen" time per virtual core in units of
timebase ticks, and to report the stolen time to the guest using the
dispatch trace log (DTL).  The guest can register an area of memory
for the DTL for a given vcpu.  The DTL is a ring buffer where KVM
fills in one entry every time it enters the guest for that vcpu.

Stolen time is measured as time when the virtual core is not running,
either because the vcore is not runnable (e.g. some of its vcpus are
executing elsewhere in the kernel or in userspace), or when the vcpu
thread that is running the vcore is preempted.  This includes time
when all the vcpus are idle (i.e. have executed the H_CEDE hypercall),
which is OK because the guest accounts stolen time while idle as idle
time.

Each vcpu keeps a record of how much stolen time has been reported to
the guest for that vcpu so far.  When we are about to enter the guest,
we create a new DTL entry (if the guest vcpu has a DTL) and report the
difference between total stolen time for the vcore and stolen time
reported so far for the vcpu as the "enqueue to dispatch" time in the
DTL entry.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/include/asm/kvm_host.h

@@ -268,6 +268,9 @@ struct kvmppc_vcore {
 	struct list_head runnable_threads;
 	spinlock_t lock;
 	wait_queue_head_t wq;
+	u64 stolen_tb;
+	u64 preempt_tb;
+	struct kvm_vcpu *runner;
 };
 
 #define VCORE_ENTRY_COUNT(vc)	((vc)->entry_exit_count & 0xff)
@@ -516,6 +519,7 @@ struct kvm_vcpu_arch {
 	struct kvmppc_vpa dtl;
 	struct dtl_entry *dtl_ptr;
 	unsigned long dtl_index;
+	u64 stolen_logged;
 	struct kvmppc_vpa slb_shadow;
 #endif
 };

arch/powerpc/kvm/book3s_hv.c

@@ -60,12 +60,20 @@ static int kvmppc_hv_setup_rma(struct kvm_vcpu *vcpu);
 
 void kvmppc_core_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
+	struct kvmppc_vcore *vc = vcpu->arch.vcore;
+
 	local_paca->kvm_hstate.kvm_vcpu = vcpu;
-	local_paca->kvm_hstate.kvm_vcore = vcpu->arch.vcore;
+	local_paca->kvm_hstate.kvm_vcore = vc;
+	if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE)
+		vc->stolen_tb += mftb() - vc->preempt_tb;
 }
 
 void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	struct kvmppc_vcore *vc = vcpu->arch.vcore;
+
+	if (vc->runner == vcpu && vc->vcore_state != VCORE_INACTIVE)
+		vc->preempt_tb = mftb();
 }
 
 void kvmppc_set_msr(struct kvm_vcpu *vcpu, u64 msr)
@@ -305,6 +313,35 @@ static void kvmppc_update_vpas(struct kvm_vcpu *vcpu)
 	spin_unlock(&vcpu->arch.vpa_update_lock);
 }
 
+static void kvmppc_create_dtl_entry(struct kvm_vcpu *vcpu,
+				    struct kvmppc_vcore *vc)
+{
+	struct dtl_entry *dt;
+	struct lppaca *vpa;
+	unsigned long old_stolen;
+
+	dt = vcpu->arch.dtl_ptr;
+	vpa = vcpu->arch.vpa.pinned_addr;
+	old_stolen = vcpu->arch.stolen_logged;
+	vcpu->arch.stolen_logged = vc->stolen_tb;
+	if (!dt || !vpa)
+		return;
+	memset(dt, 0, sizeof(struct dtl_entry));
+	dt->dispatch_reason = 7;
+	dt->processor_id = vc->pcpu + vcpu->arch.ptid;
+	dt->timebase = mftb();
+	dt->enqueue_to_dispatch_time = vc->stolen_tb - old_stolen;
+	dt->srr0 = kvmppc_get_pc(vcpu);
+	dt->srr1 = vcpu->arch.shregs.msr;
+	++dt;
+	if (dt == vcpu->arch.dtl.pinned_end)
+		dt = vcpu->arch.dtl.pinned_addr;
+	vcpu->arch.dtl_ptr = dt;
+	/* order writing *dt vs. writing vpa->dtl_idx */
+	smp_wmb();
+	vpa->dtl_idx = ++vcpu->arch.dtl_index;
+}
+
 int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 {
 	unsigned long req = kvmppc_get_gpr(vcpu, 3);
@@ -568,6 +605,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
 			INIT_LIST_HEAD(&vcore->runnable_threads);
 			spin_lock_init(&vcore->lock);
 			init_waitqueue_head(&vcore->wq);
+			vcore->preempt_tb = mftb();
 		}
 		kvm->arch.vcores[core] = vcore;
 	}
@@ -580,6 +618,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
 	++vcore->num_threads;
 	spin_unlock(&vcore->lock);
 	vcpu->arch.vcore = vcore;
+	vcpu->arch.stolen_logged = vcore->stolen_tb;
 
 	vcpu->arch.cpu_type = KVM_CPU_3S_64;
 	kvmppc_sanity_check(vcpu);
@@ -803,6 +842,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	vc->nap_count = 0;
 	vc->entry_exit_count = 0;
 	vc->vcore_state = VCORE_RUNNING;
+	vc->stolen_tb += mftb() - vc->preempt_tb;
 	vc->in_guest = 0;
 	vc->pcpu = smp_processor_id();
 	vc->napping_threads = 0;
@@ -812,6 +852,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 		    vcpu->arch.slb_shadow.update_pending ||
 		    vcpu->arch.dtl.update_pending)
 			kvmppc_update_vpas(vcpu);
+		kvmppc_create_dtl_entry(vcpu, vc);
 	}
 	/* Grab any remaining hw threads so they can't go into the kernel */
 	for (i = ptid; i < threads_per_core; ++i)
@@ -869,6 +910,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	spin_lock(&vc->lock);
  out:
 	vc->vcore_state = VCORE_INACTIVE;
+	vc->preempt_tb = mftb();
 	list_for_each_entry_safe(vcpu, vnext, &vc->runnable_threads,
 				 arch.run_list) {
 		if (vcpu->arch.ret != RESUME_GUEST) {
@@ -967,6 +1009,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 			spin_lock(&vc->lock);
 			continue;
 		}
+		vc->runner = vcpu;
 		n_ceded = 0;
 		list_for_each_entry(v, &vc->runnable_threads, arch.run_list)
 			n_ceded += v->arch.ceded;
@@ -986,6 +1029,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 				wake_up(&v->arch.cpu_run);
 			}
 		}
+		vc->runner = NULL;
 	}
 
 	if (signal_pending(current)) {