[PATCH 1/2] KVM: introduce kvm_vcpu_on_spin

[Andy Whitcroft]

From: Zhai, Edwin <edwin.zhai at intel.com>

Introduce kvm_vcpu_on_spin, to be used by VMX/SVM to yield processing
once the cpu detects pause-based looping.

Signed-off-by: "Zhai, Edwin" <edwin.zhai at intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti at redhat.com>
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 include/linux/kvm_host.h |    1 +
 virt/kvm/kvm_main.c      |   15 +++++++++++++++
 2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b7bbb5d..b5bcb4f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -266,6 +266,7 @@ int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn);
 void mark_page_dirty(struct kvm *kvm, gfn_t gfn);
 
 void kvm_vcpu_block(struct kvm_vcpu *vcpu);
+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);
 void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7495ce3..faa40d9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1705,6 +1705,21 @@ void kvm_resched(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_resched);
 
+void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu)
+{
+	ktime_t expires;
+	DEFINE_WAIT(wait);
+
+	prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
+
+	/* Sleep for 100 us, and hope lock-holder got scheduled */
+	expires = ktime_add_ns(ktime_get(), 100000UL);
+	schedule_hrtimeout(&expires, HRTIMER_MODE_ABS);
+
+	finish_wait(&vcpu->wq, &wait);
+}
+EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin);
+
 static int kvm_vcpu_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct kvm_vcpu *vcpu = vma->vm_file->private_data;
-- 
1.7.0