[PATCH 2/2][RFC] Kernel changes for HPET legacy mode (v7)

[Beth Kon <eak@us.ibm.com>]

When kvm is in hpet_legacy_mode, the hpet is providing the 
timer interrupt and the pit should not be. So in legacy mode, the pit timer is
destroyed, but the *state* of the pit is maintained. So if kvm or the guest
tries to modify the state of the pit, this modification is accepted, *except* 
that the timer isn't actually started. When we exit hpet_legacy_mode, 
the current state of the pit (which is up to date since we've been 
accepting modifications) is used to restart the pit timer.

The saved_mode code in kvm_pit_load_count temporarily changes mode to 
0xff in order to destroy the timer, but then restores the actual value,
again maintaining "current" state of the pit for possible later reenablement.

changes from v6:

- Added ioctl interface for legacy mode in order not to break the abi.


Signed-off-by: Beth Kon <eak@us.ibm.com>

diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index 708b9c3..25cae50 100644
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -18,6 +18,7 @@
 #define __KVM_HAVE_GUEST_DEBUG
 #define __KVM_HAVE_MSIX
 #define __KVM_HAVE_MCE
+#define __KVM_HAVE_HPET_LEGACY_MODE
 
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 331705f..02de293 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -329,21 +329,32 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 	case 1:
         /* FIXME: enhance mode 4 precision */
 	case 4:
-		create_pit_timer(ps, val, 0);
+		if (!ps->hpet_legacy_mode)
+			create_pit_timer(ps, val, 0);
 		break;
 	case 2:
 	case 3:
-		create_pit_timer(ps, val, 1);
+		if (!ps->hpet_legacy_mode)
+			create_pit_timer(ps, val, 1);
 		break;
 	default:
 		destroy_pit_timer(&ps->pit_timer);
 	}
 }
 
-void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val)
+void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_start)
 {
+	u8 saved_mode;
 	mutex_lock(&kvm->arch.vpit->pit_state.lock);
-	pit_load_count(kvm, channel, val);
+	if (hpet_legacy_start) {
+		/* save existing mode for later reenablement */
+		saved_mode = kvm->arch.vpit->pit_state.channels[0].mode;
+		kvm->arch.vpit->pit_state.channels[0].mode = 0xff; /* disable timer */
+		pit_load_count(kvm, channel, val);
+		kvm->arch.vpit->pit_state.channels[0].mode = saved_mode;
+	} else {
+		pit_load_count(kvm, channel, val);
+	}
 	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
 }
 
@@ -548,6 +559,7 @@ void kvm_pit_reset(struct kvm_pit *pit)
 	struct kvm_kpit_channel_state *c;
 
 	mutex_lock(&pit->pit_state.lock);
+	pit->pit_state.hpet_legacy_mode = 0;
 	for (i = 0; i < 3; i++) {
 		c = &pit->pit_state.channels[i];
 		c->mode = 0xff;
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index b267018..b5967ca 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -21,6 +21,7 @@ struct kvm_kpit_channel_state {
 
 struct kvm_kpit_state {
 	struct kvm_kpit_channel_state channels[3];
+	u8 hpet_legacy_mode;
 	struct kvm_timer pit_timer;
 	bool is_periodic;
 	u32    speaker_data_on;
@@ -49,7 +50,7 @@ struct kvm_pit {
 #define KVM_PIT_CHANNEL_MASK	    0x3
 
 void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu);
-void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val);
+void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val, int hpet_legacy_start);
 struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags);
 void kvm_free_pit(struct kvm *kvm);
 void kvm_pit_reset(struct kvm_pit *pit);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6025e5b..8562eeb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1134,6 +1134,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_ASSIGN_DEV_IRQ:
 	case KVM_CAP_IRQFD:
 	case KVM_CAP_PIT2:
+	case KVM_CAP_HPET_LEGACY_MODE:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
@@ -1986,7 +1987,24 @@ static int kvm_vm_ioctl_set_pit(struct kvm *kvm, struct kvm_pit_state *ps)
 	int r = 0;
 
 	memcpy(&kvm->arch.vpit->pit_state, ps, sizeof(struct kvm_pit_state));
-	kvm_pit_load_count(kvm, 0, ps->channels[0].count);
+	kvm_pit_load_count(kvm, 0, ps->channels[0].count, 0);
+	return r;
+}
+
+static int kvm_vm_ioctl_get_hpet_legacy_mode(struct kvm *kvm, u8 *mode)
+{
+	int r = 0;
+	*mode = kvm->arch.vpit->pit_state.hpet_legacy_mode;
+	return r;
+}
+
+static int kvm_vm_ioctl_set_hpet_legacy_mode(struct kvm *kvm, u8 *mode)
+{
+	int r = 0, start = 0;
+	if (kvm->arch.vpit->pit_state.hpet_legacy_mode == 0 && *mode == 1)
+		start = 1;
+	kvm->arch.vpit->pit_state.hpet_legacy_mode = *mode;
+	kvm_pit_load_count(kvm, 0, kvm->arch.vpit->pit_state.channels[0].count, start);
 	return r;
 }
 
@@ -2047,6 +2065,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		struct kvm_pit_state ps;
 		struct kvm_memory_alias alias;
 		struct kvm_pit_config pit_config;
+		u8 hpet_legacy_mode;
 	} u;
 
 	switch (ioctl) {
@@ -2227,6 +2246,32 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		r = 0;
 		break;
 	}
+	case KVM_GET_HPET_LEGACY_MODE: {
+		r = -ENXIO;
+		if (!kvm->arch.vpit)
+			goto out;
+		r = kvm_vm_ioctl_get_hpet_legacy_mode(kvm, &u.hpet_legacy_mode);
+		if (r)
+			goto out;
+		r = -EFAULT;
+		if (copy_to_user(argp, &u.ps, sizeof(u.hpet_legacy_mode)))
+			goto out;
+		r = 0;
+		break;
+	}
+	case KVM_SET_HPET_LEGACY_MODE: {
+		r = -EFAULT;
+		if (copy_from_user(&u.hpet_legacy_mode, argp, sizeof(u.hpet_legacy_mode)))
+			goto out;
+		r = -ENXIO;
+		if (!kvm->arch.vpit)
+			goto out;
+		r = kvm_vm_ioctl_set_hpet_legacy_mode(kvm, &u.hpet_legacy_mode);
+		if (r)
+			goto out;
+		r = 0;
+		break;
+	}
 	case KVM_REINJECT_CONTROL: {
 		struct kvm_reinject_control control;
 		r =  -EFAULT;
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 38ff31e..202cf6e 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -438,6 +438,9 @@ struct kvm_trace_rec {
 #define KVM_CAP_PIT2 33
 #endif
 #define KVM_CAP_SET_BOOT_CPU_ID 34
+#ifdef __KVM_HAVE_HPET_LEGACY_MODE
+#define KVM_CAP_HPET_LEGACY_MODE 35
+#endif
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -613,6 +616,9 @@ struct kvm_debug_guest {
 #define KVM_IA64_VCPU_GET_STACK   _IOR(KVMIO,  0x9a, void *)
 #define KVM_IA64_VCPU_SET_STACK   _IOW(KVMIO,  0x9b, void *)
 
+#define KVM_GET_HPET_LEGACY_MODE   _IOR(KVMIO,   0x9c, __u8)
+#define KVM_SET_HPET_LEGACY_MODE   _IOWR(KVMIO,   0x9d, __u8)
+
 #define KVM_TRC_INJ_VIRQ         (KVM_TRC_HANDLER + 0x02)
 #define KVM_TRC_REDELIVER_EVT    (KVM_TRC_HANDLER + 0x03)
 #define KVM_TRC_PEND_INTR        (KVM_TRC_HANDLER + 0x04)