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>

5 files changed, 54 insertions, 16 deletions

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 7343872890a2..dd17537b9a9d 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -148,6 +148,7 @@ struct kvm_vcpu_stat {
         u32 instruction_sigp_restart;
         u32 diagnose_10;
         u32 diagnose_44;
+        u32 diagnose_9c;
 };
 
 struct kvm_s390_io_info {
diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index a353f0ea45c2..2d2ae327b747 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -53,6 +53,29 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu)
         return 0;
 }
 
+static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
+{
+        struct kvm *kvm = vcpu->kvm;
+        struct kvm_vcpu *tcpu;
+        int tid;
+        int i;
+
+        tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
+        vcpu->stat.diagnose_9c++;
+        VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d", tid);
+
+        if (tid == vcpu->vcpu_id)
+                return 0;
+
+        kvm_for_each_vcpu(i, tcpu, kvm)
+                if (tcpu->vcpu_id == tid) {
+                        kvm_vcpu_yield_to(tcpu);
+                        break;
+                }
+
+        return 0;
+}
+
 static int __diag_ipl_functions(struct kvm_vcpu *vcpu)
 {
         unsigned int reg = vcpu->arch.sie_block->ipa & 0xf;
@@ -89,6 +112,8 @@ int kvm_s390_handle_diag(struct kvm_vcpu *vcpu)
                 return diag_release_pages(vcpu);
         case 0x44:
                 return __diag_time_slice_end(vcpu);
+        case 0x9c:
+                return __diag_time_slice_end_directed(vcpu);
         case 0x308:
                 return __diag_ipl_functions(vcpu);
         default:
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index d30c8350b949..fd98914a36f1 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -74,6 +74,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
         { "instruction_sigp_restart", VCPU_STAT(instruction_sigp_restart) },
         { "diagnose_10", VCPU_STAT(diagnose_10) },
         { "diagnose_44", VCPU_STAT(diagnose_44) },
+        { "diagnose_9c", VCPU_STAT(diagnose_9c) },
         { NULL }
 };
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6f343307d72b..cae342d29d1b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -461,6 +461,7 @@ void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot,
 
 void kvm_vcpu_block(struct kvm_vcpu *vcpu);
 void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
+bool kvm_vcpu_yield_to(struct kvm_vcpu *target);
 void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
 void kvm_resched(struct kvm_vcpu *vcpu);
 void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
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);
                 }
         }
 }