[PATCH RFC 2/4] Add yield hypercall for KVM guests

[Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>]

Add KVM hypercall for yielding vcpu timeslice.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

---
 arch/x86/include/asm/kvm_para.h |    1 +
 arch/x86/kvm/x86.c              |    7 ++++++-
 include/linux/kvm.h             |    1 +
 include/linux/kvm_para.h        |    1 +
 4 files changed, 9 insertions(+), 1 deletion(-)

Index: current/arch/x86/include/asm/kvm_para.h
===================================================================
--- current.orig/arch/x86/include/asm/kvm_para.h
+++ current/arch/x86/include/asm/kvm_para.h
@@ -16,6 +16,7 @@
 #define KVM_FEATURE_CLOCKSOURCE		0
 #define KVM_FEATURE_NOP_IO_DELAY	1
 #define KVM_FEATURE_MMU_OP		2
+#define KVM_FEATURE_YIELD		4
 /* This indicates that the new set of kvmclock msrs
  * are available. The use of 0x11 and 0x12 is deprecated
  */
Index: current/arch/x86/kvm/x86.c
===================================================================
--- current.orig/arch/x86/kvm/x86.c
+++ current/arch/x86/kvm/x86.c
@@ -1618,6 +1618,7 @@ int kvm_dev_ioctl_check_extension(long e
 	case KVM_CAP_PCI_SEGMENT:
 	case KVM_CAP_DEBUGREGS:
 	case KVM_CAP_X86_ROBUST_SINGLESTEP:
+	case KVM_CAP_YIELD_HYPERCALL:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -1993,7 +1994,8 @@ static void do_cpuid_ent(struct kvm_cpui
 		entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
 			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
 			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
-			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
+			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
+			     (1 << KVM_FEATURE_YIELD);
 		entry->ebx = 0;
 		entry->ecx = 0;
 		entry->edx = 0;
@@ -4245,6 +4247,9 @@ int kvm_emulate_hypercall(struct kvm_vcp
 	case KVM_HC_MMU_OP:
 		r = kvm_pv_mmu_op(vcpu, a0, hc_gpa(vcpu, a1, a2), &ret);
 		break;
+	case KVM_HC_YIELD:
+		ret = 0;
+		yield();
 	default:
 		ret = -KVM_ENOSYS;
 		break;
Index: current/include/linux/kvm.h
===================================================================
--- current.orig/include/linux/kvm.h
+++ current/include/linux/kvm.h
@@ -524,6 +524,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_PPC_OSI 52
 #define KVM_CAP_PPC_UNSET_IRQ 53
 #define KVM_CAP_ENABLE_CAP 54
+#define KVM_CAP_YIELD_HYPERCALL	55
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
Index: current/include/linux/kvm_para.h
===================================================================
--- current.orig/include/linux/kvm_para.h
+++ current/include/linux/kvm_para.h
@@ -17,6 +17,7 @@
 
 #define KVM_HC_VAPIC_POLL_IRQ		1
 #define KVM_HC_MMU_OP			2
+#define KVM_HC_YIELD                    3
 
 /*
  * hypercalls use architecture specific