KVM: Per-vcpu statistics

Make the exit statistics per-vcpu instead of global.  This gives a 3.5%
boost when running one virtual machine per core on my two socket dual core
(4 cores total) machine.

Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index b94010d..73ffbff 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -448,7 +448,7 @@
 	if (is_io_pte(*shadow_pte))
 		return 1;
 
-	++kvm_stat.pf_fixed;
+	++vcpu->stat.pf_fixed;
 	kvm_mmu_audit(vcpu, "post page fault (fixed)");
 
 	return write_pt;