KVM: Emulate hlt in the kernel

By sleeping in the kernel when hlt is executed, we simplify the in-kernel
guest interrupt path considerably.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 35 insertions, 6 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index ffbdadd87971..4384364fc0c8 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -76,6 +76,7 @@ static struct kvm_stats_debugfs_item {
         { "signal_exits", STAT_OFFSET(signal_exits) },
         { "irq_window", STAT_OFFSET(irq_window_exits) },
         { "halt_exits", STAT_OFFSET(halt_exits) },
+        { "halt_wakeup", STAT_OFFSET(halt_wakeup) },
         { "request_irq", STAT_OFFSET(request_irq_exits) },
         { "irq_exits", STAT_OFFSET(irq_exits) },
         { "light_exits", STAT_OFFSET(light_exits) },
@@ -248,6 +249,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
         vcpu->mmu.root_hpa = INVALID_PAGE;
         vcpu->kvm = kvm;
         vcpu->vcpu_id = id;
+        init_waitqueue_head(&vcpu->wq);
 
         page = alloc_page(GFP_KERNEL | __GFP_ZERO);
         if (!page) {
@@ -1307,15 +1309,41 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 }
 EXPORT_SYMBOL_GPL(emulate_instruction);
 
-int kvm_emulate_halt(struct kvm_vcpu *vcpu)
+/*
+ * The vCPU has executed a HLT instruction with in-kernel mode enabled.
+ */
+static void kvm_vcpu_kernel_halt(struct kvm_vcpu *vcpu)
 {
-        if (vcpu->irq_summary ||
-                (irqchip_in_kernel(vcpu->kvm) && kvm_cpu_has_interrupt(vcpu)))
-                return 1;
+        DECLARE_WAITQUEUE(wait, current);
+
+        add_wait_queue(&vcpu->wq, &wait);
+
+        /*
+         * We will block until either an interrupt or a signal wakes us up
+         */
+        while(!(irqchip_in_kernel(vcpu->kvm) && kvm_cpu_has_interrupt(vcpu))
+              && !vcpu->irq_summary
+              && !signal_pending(current)) {
+                set_current_state(TASK_INTERRUPTIBLE);
+                vcpu_put(vcpu);
+                schedule();
+                vcpu_load(vcpu);
+        }
 
-        vcpu->run->exit_reason = KVM_EXIT_HLT;
+        remove_wait_queue(&vcpu->wq, &wait);
+        set_current_state(TASK_RUNNING);
+}
+
+int kvm_emulate_halt(struct kvm_vcpu *vcpu)
+{
         ++vcpu->stat.halt_exits;
-        return 0;
+        if (irqchip_in_kernel(vcpu->kvm)) {
+                kvm_vcpu_kernel_halt(vcpu);
+                return 1;
+        } else {
+                vcpu->run->exit_reason = KVM_EXIT_HLT;
+                return 0;
+        }
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_halt);
 
@@ -2916,6 +2944,7 @@ static long kvm_dev_ioctl(struct file *filp,
 
                 switch (ext) {
                 case KVM_CAP_IRQCHIP:
+                case KVM_CAP_HLT:
                         r = 1;
                         break;
                 default: