[PATCH 3/5] KVM: add KVM_USER_EXIT vm ioctl for userspace exit

[Radim KrÄmÃÅ]

The guest can use KVM_USER_EXIT instead of a signal-based exiting to
userspace.  Availability depends on KVM_CAP_USER_EXIT.
Only x86 is implemented so far.

It would be cleaner to use 'unsigned long' to store the vcpu_id, but I
really don't like its variable size and 'u64' will be same/bigger for
few for more years.

Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
---
 Documentation/virtual/kvm/api.txt | 30 ++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c                |  1 +
 include/uapi/linux/kvm.h          |  8 ++++++++
 virt/kvm/kvm_main.c               | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 74 insertions(+)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 3c714d43a717..5cf25a15fc6f 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3020,6 +3020,36 @@ Returns: 0 on success, -1 on error
 
 Queues an SMI on the thread's vcpu.
 
+
+4.97 KVM_USER_EXIT
+
+Capability: KVM_CAP_USER_EXIT
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_user_exit (in)
+Returns: 0 on success,
+         -EFAULT if the parameter couldn't be read,
+         -EINVAL if 'reserved' is not zeroed,
+         -ENOENT if VCPU with 'vcpu_id' is not present
+
+struct kvm_user_exit {
+	__u64 vcpu_id;
+	__u32 reserved[14];
+};
+
+Make vcpu_id exit to userspace as soon as possible.  If the VCPU is not running
+in kernel at the time, it will exit early on the next call to KVM_RUN.
+If the VCPU was going to exit because of other reasons when KVM_USER_EXIT was
+issued, it will keep the original exit reason and not exit early on next
+KVM_RUN.
+If VCPU exited because of KVM_USER_EXIT, the exit reason is KVM_EXIT_REQUEST.
+
+This ioctl has very similar effect (same sans some races on userspace exit) as
+sending a signal (that is blocked in userspace and set in KVM_SET_SIGNAL_MASK)
+to the VCPU thread.
+
+
+
 5. The kvm_run structure
 ------------------------
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5d790fdfc2e..61f35944dd53 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2465,6 +2465,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ASSIGN_DEV_IRQ:
 	case KVM_CAP_PCI_2_3:
 #endif
+	case KVM_CAP_USER_EXIT:
 		r = 1;
 		break;
 	case KVM_CAP_X86_SMM:
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d996a7cdb4d2..79316489346c 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -826,6 +826,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_X86_SMM 117
 #define KVM_CAP_MULTI_ADDRESS_SPACE 118
 #define KVM_CAP_SPLIT_IRQCHIP 119
+#define KVM_CAP_USER_EXIT 120
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1008,6 +1009,11 @@ struct kvm_device_attr {
 	__u64	addr;		/* userspace address of attr data */
 };
 
+struct kvm_user_exit {
+	__u64 vcpu_id;        /* the 'unsigned long' used in KVM_CREATE_VCPU */
+	__u32 reserved[14];
+};
+
 #define  KVM_DEV_VFIO_GROUP			1
 #define   KVM_DEV_VFIO_GROUP_ADD			1
 #define   KVM_DEV_VFIO_GROUP_DEL			2
@@ -1119,6 +1125,8 @@ struct kvm_s390_ucas_mapping {
 #define KVM_ARM_SET_DEVICE_ADDR	  _IOW(KVMIO,  0xab, struct kvm_arm_device_addr)
 /* Available with KVM_CAP_PPC_RTAS */
 #define KVM_PPC_RTAS_DEFINE_TOKEN _IOW(KVMIO,  0xac, struct kvm_rtas_token_args)
+/* Available with KVM_CAP_USER_EXIT */
+#define KVM_USER_EXIT             _IOW(KVMIO,  0xad, struct kvm_user_exit)
 
 /* ioctl for vm fd */
 #define KVM_CREATE_DEVICE	  _IOWR(KVMIO,  0xe0, struct kvm_create_device)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b34a328fdac1..024428b64812 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2644,6 +2644,32 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	return kvm_vm_ioctl_check_extension(kvm, arg);
 }
 
+int kvm_vm_ioctl_user_exit(struct kvm *kvm, struct kvm_user_exit *info)
+{
+	/* Casting vcpu_id to int is intended and matches the behavior of
+	 * KVM_CREATE_VCPU, where we cast from unsigned long.
+	 */
+	int vcpu_id = info->vcpu_id;
+	int idx;
+	struct kvm_vcpu *vcpu;
+	const struct kvm_user_exit valid = {.vcpu_id = info->vcpu_id};
+
+	BUILD_BUG_ON(sizeof(struct kvm_user_exit) != 64);
+
+	if (memcmp(info, &valid, sizeof(valid)))
+		return -EINVAL;
+
+	kvm_for_each_vcpu(idx, vcpu, kvm)
+		if (vcpu->vcpu_id == vcpu_id) {
+			kvm_make_request(KVM_REQ_EXIT, vcpu);
+			kvm_vcpu_kick(vcpu);
+
+			return 0;
+		}
+
+	return -ENOENT;
+}
+
 static long kvm_vm_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -2779,6 +2805,15 @@ out_free_irq_routing:
 		vfree(entries);
 		break;
 	}
+	case KVM_USER_EXIT: {
+		struct kvm_user_exit info;
+
+		r = -EFAULT;
+		if (copy_from_user(&info, argp, sizeof(info)))
+			goto out;
+		r = kvm_vm_ioctl_user_exit(kvm, &info);
+		break;
+	}
 #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */
 	case KVM_CREATE_DEVICE: {
 		struct kvm_create_device cd;
-- 
2.5.0

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