[PATCH 1/3v2] kvm-s390: Implement the directed yield (diag 9c) hypervisor call for KVM

[Christian Borntraeger <borntraeger@de.ibm.com>]

From: Konstantin Weitz <WEITZKON@de.ibm.com>

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.

Signed-off-by: Konstantin Weitz <WEITZKON@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |    1 +
 arch/s390/kvm/diag.c             |   41 ++++++++++++++++++++++++++++++++++++++
 arch/s390/kvm/kvm-s390.c         |    1 +
 3 files changed, 43 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 7343872..dd17537 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 a353f0e..022962b 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -53,6 +53,45 @@ 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) {
+			struct task_struct *task = NULL;
+			struct pid *pid;
+			rcu_read_lock();
+			pid = rcu_dereference(tcpu->pid);
+			if (pid)
+				task = get_pid_task(tcpu->pid, PIDTYPE_PID);
+			rcu_read_unlock();
+			if (!task)
+				break;
+			if (task->flags & PF_VCPU) {
+				put_task_struct(task);
+				break;
+			}
+			if (yield_to(task, 1)) {
+				put_task_struct(task);
+				return 0;
+			}
+			put_task_struct(task);
+		}
+	}
+	return 0;
+}
+
 static int __diag_ipl_functions(struct kvm_vcpu *vcpu)
 {
 	unsigned int reg = vcpu->arch.sie_block->ipa & 0xf;
@@ -89,6 +128,8 @@ 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 d30c835..fd98914 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 }
 };
 
-- 
1.7.9.6