[PATCH v4 3/8] KVM Guest: Add VCPU running/pre-empted state for guest

["Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>]

From: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>

The patch adds guest code for msr between guest and hypervisor. The
msr will export the vcpu running/pre-empted information to the guest
from host. This will enable guest to intelligently send ipi to running
vcpus and set flag for pre-empted vcpus. This will prevent waiting for
vcpus that are not running.

Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
---
 arch/x86/include/asm/kvm_para.h |   13 +++++++++++++
 arch/x86/kernel/kvm.c           |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 2f7712e..5dfb975 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -23,6 +23,7 @@
 #define KVM_FEATURE_ASYNC_PF		4
 #define KVM_FEATURE_STEAL_TIME		5
 #define KVM_FEATURE_PV_EOI		6
+#define KVM_FEATURE_VCPU_STATE          7
 
 /* The last 8 bits are used to indicate how to interpret the flags field
  * in pvclock structure. If no bits are set, all flags are ignored.
@@ -39,6 +40,7 @@
 #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
 #define MSR_KVM_STEAL_TIME  0x4b564d03
 #define MSR_KVM_PV_EOI_EN      0x4b564d04
+#define MSR_KVM_VCPU_STATE  0x4b564d05
 
 struct kvm_steal_time {
 	__u64 steal;
@@ -51,6 +53,17 @@ struct kvm_steal_time {
 #define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1)))
 #define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1)
 
+struct kvm_vcpu_state {
+	__u64 state;
+	__u32 pad[14];
+};
+/* bits in vcpu_state->state */
+#define KVM_VCPU_STATE_IN_GUEST_MODE 0
+#define KVM_VCPU_STATE_SHOULD_FLUSH  1
+
+#define KVM_VCPU_STATE_ALIGN_BITS 5
+#define KVM_VCPU_STATE_VALID_BITS ((-1ULL << (KVM_VCPU_STATE_ALIGN_BITS + 1)))
+
 #define KVM_MAX_MMU_OP_BATCH           32
 
 #define KVM_ASYNC_PF_ENABLED			(1 << 0)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index c1d61ee..37e6599 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -66,6 +66,9 @@ static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
 static int has_steal_clock = 0;
 
+DEFINE_PER_CPU(struct kvm_vcpu_state, vcpu_state) __aligned(64);
+static int has_vcpu_state;
+
 /*
  * No need for any "IO delay" on KVM
  */
@@ -302,6 +305,22 @@ static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 	apic_write(APIC_EOI, APIC_EOI_ACK);
 }
 
+static void kvm_register_vcpu_state(void)
+{
+	int cpu = smp_processor_id();
+	struct kvm_vcpu_state *v_state;
+
+	if (!has_vcpu_state)
+		return;
+
+	v_state = &per_cpu(vcpu_state, cpu);
+	memset(v_state, 0, sizeof(*v_state));
+
+	wrmsrl(MSR_KVM_VCPU_STATE, (__pa(v_state) | KVM_MSR_ENABLED));
+	printk(KERN_INFO "kvm-vcpustate: cpu %d, msr %lx\n",
+		cpu, __pa(v_state));
+}
+
 void __cpuinit kvm_guest_cpu_init(void)
 {
 	if (!kvm_para_available())
@@ -330,6 +349,9 @@ void __cpuinit kvm_guest_cpu_init(void)
 
 	if (has_steal_clock)
 		kvm_register_steal_time();
+
+	if (has_vcpu_state)
+		kvm_register_vcpu_state();
 }
 
 static void kvm_pv_disable_apf(void)
@@ -393,6 +415,14 @@ void kvm_disable_steal_time(void)
 	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 }
 
+void kvm_disable_vcpu_state(void)
+{
+	if (!has_vcpu_state)
+		return;
+
+	wrmsr(MSR_KVM_VCPU_STATE, 0, 0);
+}
+
 #ifdef CONFIG_SMP
 static void __init kvm_smp_prepare_boot_cpu(void)
 {
@@ -410,6 +440,7 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
 
 static void kvm_guest_cpu_offline(void *dummy)
 {
+	kvm_disable_vcpu_state();
 	kvm_disable_steal_time();
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 		wrmsrl(MSR_KVM_PV_EOI_EN, 0);
@@ -469,6 +500,11 @@ void __init kvm_guest_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 		apic_set_eoi_write(kvm_guest_apic_eoi_write);
 
+#ifdef CONFIG_PARAVIRT_TLB_FLUSH
+	if (kvm_para_has_feature(KVM_FEATURE_VCPU_STATE))
+		has_vcpu_state = 1;
+#endif
+
 #ifdef CONFIG_SMP
 	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
 	register_cpu_notifier(&kvm_cpu_notifier);