KVM: s390: Implement the directed yield (diag 9c) hypervisor call for KVM

This patch implements the directed yield hypercall found on other
System z hypervisors. It delegates execution time to the virtual cpu
specified in the instruction's parameter.

Useful to avoid long spinlock waits in the guest.

Christian Borntraeger: moved common code in virt/kvm/

Signed-off-by: Konstantin Weitz <WEITZKON@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 26 insertions, 16 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1847c762d8d9..7e140683ff14 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1543,6 +1543,31 @@ void kvm_resched(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_resched);
 
+bool kvm_vcpu_yield_to(struct kvm_vcpu *target)
+{
+        struct pid *pid;
+        struct task_struct *task = NULL;
+
+        rcu_read_lock();
+        pid = rcu_dereference(target->pid);
+        if (pid)
+                task = get_pid_task(target->pid, PIDTYPE_PID);
+        rcu_read_unlock();
+        if (!task)
+                return false;
+        if (task->flags & PF_VCPU) {
+                put_task_struct(task);
+                return false;
+        }
+        if (yield_to(task, 1)) {
+                put_task_struct(task);
+                return true;
+        }
+        put_task_struct(task);
+        return false;
+}
+EXPORT_SYMBOL_GPL(kvm_vcpu_yield_to);
+
 void kvm_vcpu_on_spin(struct kvm_vcpu *me)
 {
         struct kvm *kvm = me->kvm;
@@ -1561,8 +1586,6 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
          */
         for (pass = 0; pass < 2 && !yielded; pass++) {
                 kvm_for_each_vcpu(i, vcpu, kvm) {
-                        struct task_struct *task = NULL;
-                        struct pid *pid;
                         if (!pass && i < last_boosted_vcpu) {
                                 i = last_boosted_vcpu;
                                 continue;
@@ -1572,24 +1595,11 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
                                 continue;
                         if (waitqueue_active(&vcpu->wq))
                                 continue;
-                        rcu_read_lock();
-                        pid = rcu_dereference(vcpu->pid);
-                        if (pid)
-                                task = get_pid_task(vcpu->pid, PIDTYPE_PID);
-                        rcu_read_unlock();
-                        if (!task)
-                                continue;
-                        if (task->flags & PF_VCPU) {
-                                put_task_struct(task);
-                                continue;
-                        }
-                        if (yield_to(task, 1)) {
-                                put_task_struct(task);
+                        if (kvm_vcpu_yield_to(vcpu)) {
                                 kvm->last_boosted_vcpu = i;
                                 yielded = 1;
                                 break;
                         }
-                        put_task_struct(task);
                 }
         }
 }