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>

7 files changed, 57 insertions, 11 deletions

diff --git a/drivers/kvm/i8259.c b/drivers/kvm/i8259.c
index 40ad10462238..ee6030dc5c04 100644
--- a/drivers/kvm/i8259.c
+++ b/drivers/kvm/i8259.c
@@ -413,8 +413,11 @@ static void picdev_read(struct kvm_io_device *this,
 static void pic_irq_request(void *opaque, int level)
 {
         struct kvm *kvm = opaque;
+        struct kvm_vcpu *vcpu = kvm->vcpus[0];
 
         pic_irqchip(kvm)->output = level;
+        if (vcpu)
+                kvm_vcpu_kick(vcpu);
 }
 
 struct kvm_pic *kvm_create_pic(struct kvm *kvm)
diff --git a/drivers/kvm/irq.c b/drivers/kvm/irq.c
index 5265f8267b3b..e09cd65925d6 100644
--- a/drivers/kvm/irq.c
+++ b/drivers/kvm/irq.c
@@ -70,6 +70,10 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 {
         int ipi_pcpu = vcpu->cpu;
 
+        if (waitqueue_active(&vcpu->wq)) {
+                wake_up_interruptible(&vcpu->wq);
+                ++vcpu->stat.halt_wakeup;
+        }
         if (vcpu->guest_mode)
                 smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0, 0);
 }
diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 8d07a993af94..bb506b71797d 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -231,6 +231,7 @@ struct kvm_stat {
         u32 signal_exits;
         u32 irq_window_exits;
         u32 halt_exits;
+        u32 halt_wakeup;
         u32 request_irq_exits;
         u32 irq_exits;
         u32 light_exits;
@@ -353,6 +354,7 @@ struct kvm_vcpu {
         gva_t mmio_fault_cr2;
         struct kvm_pio_request pio;
         void *pio_data;
+        wait_queue_head_t wq;
 
         int sigset_active;
         sigset_t sigset;
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:
diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index d576451827e7..a347b61644cd 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1398,9 +1398,12 @@ static void do_interrupt_requests(struct vcpu_svm *svm,
 static void post_kvm_run_save(struct vcpu_svm *svm,
                               struct kvm_run *kvm_run)
 {
-        kvm_run->ready_for_interrupt_injection
-                = (svm->vcpu.interrupt_window_open &&
-                   svm->vcpu.irq_summary == 0);
+        if (irqchip_in_kernel(svm->vcpu.kvm))
+                kvm_run->ready_for_interrupt_injection = 1;
+        else
+                kvm_run->ready_for_interrupt_injection =
+                                         (svm->vcpu.interrupt_window_open &&
+                                          svm->vcpu.irq_summary == 0);
         kvm_run->if_flag = (svm->vmcb->save.rflags & X86_EFLAGS_IF) != 0;
         kvm_run->cr8 = get_cr8(&svm->vcpu);
         kvm_run->apic_base = kvm_get_apic_base(&svm->vcpu);
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index c4cc17cc00f7..7ec8cf84e6ea 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1961,8 +1961,12 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu,
         kvm_run->if_flag = (vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) != 0;
         kvm_run->cr8 = get_cr8(vcpu);
         kvm_run->apic_base = kvm_get_apic_base(vcpu);
-        kvm_run->ready_for_interrupt_injection = (vcpu->interrupt_window_open &&
-                                                  vcpu->irq_summary == 0);
+        if (irqchip_in_kernel(vcpu->kvm))
+                kvm_run->ready_for_interrupt_injection = 1;
+        else
+                kvm_run->ready_for_interrupt_injection =
+                                        (vcpu->interrupt_window_open &&
+                                         vcpu->irq_summary == 0);
 }
 
 static int handle_interrupt_window(struct kvm_vcpu *vcpu,
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 997bb3e46f1e..b0a13d1b34cc 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -283,6 +283,7 @@ struct kvm_signal_mask {
  * Extension capability list.
  */
 #define KVM_CAP_IRQCHIP   0
+#define KVM_CAP_HLT       1
 
 /*
  * ioctls for VM fds