KVM: PPC: Book3S HV: Speed up wakeups of CPUs on HV KVM

Currently, we wake up a CPU by sending a host IPI with
smp_send_reschedule() to thread 0 of that core, which will take all
threads out of the guest, and cause them to re-evaluate their
interrupt status on the way back in.

This adds a mechanism to differentiate real host IPIs from IPIs sent
by KVM for guest threads to poke each other, in order to target the
guest threads precisely when possible and avoid that global switch of
the core to host state.

We then use this new facility in the in-kernel XICS code.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 25 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 82ba00f68b07..16191915e8d0 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -66,6 +66,31 @@
 static void kvmppc_end_cede(struct kvm_vcpu *vcpu);
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
 
+void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu)
+{
+        int me;
+        int cpu = vcpu->cpu;
+        wait_queue_head_t *wqp;
+
+        wqp = kvm_arch_vcpu_wq(vcpu);
+        if (waitqueue_active(wqp)) {
+                wake_up_interruptible(wqp);
+                ++vcpu->stat.halt_wakeup;
+        }
+
+        me = get_cpu();
+
+        /* CPU points to the first thread of the core */
+        if (cpu != me && cpu >= 0 && cpu < nr_cpu_ids) {
+                int real_cpu = cpu + vcpu->arch.ptid;
+                if (paca[real_cpu].kvm_hstate.xics_phys)
+                        xics_wake_cpu(real_cpu);
+                else if (cpu_online(cpu))
+                        smp_send_reschedule(cpu);
+        }
+        put_cpu();
+}
+
 /*
  * We use the vcpu_load/put functions to measure stolen time.
  * Stolen time is counted as time when either the vcpu is able to
@@ -985,7 +1010,6 @@ static void kvmppc_end_cede(struct kvm_vcpu *vcpu)
 }
 
 extern int __kvmppc_vcore_entry(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu);
-extern void xics_wake_cpu(int cpu);
 
 static void kvmppc_remove_runnable(struct kvmppc_vcore *vc,
                                    struct kvm_vcpu *vcpu)