[PATCH v2 4/5] KVM: add KVM_USER_EXIT vcpu ioctl for userspace exit

["Radim Krčmář" <rkrcmar@redhat.com>]

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.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2:
  * use vcpu ioctl instead of vm one [4/5]
  * shrink kvm_user_exit from 64 to 32 bytes [4/5]

 Documentation/virtual/kvm/api.txt | 30 ++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c                | 24 ++++++++++++++++++++++++
 include/uapi/linux/kvm.h          |  7 +++++++
 virt/kvm/kvm_main.c               |  5 +++--
 4 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 3c714d43a717..c5844f0b8e7c 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: vcpu 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,
+
+struct kvm_user_exit {
+	__u8 reserved[32];
+};
+
+The ioctl is asynchronous to VCPU execution and can be issued from all threads.
+
+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 3493457ad0a1..27d777eb34e4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2466,6 +2466,7 @@ 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:
@@ -3077,6 +3078,20 @@ static int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+int kvm_vcpu_ioctl_user_exit(struct kvm_vcpu *vcpu, struct kvm_user_exit *info)
+{
+	struct kvm_user_exit valid = {};
+       BUILD_BUG_ON(sizeof(valid) != 32);
+
+	if (memcmp(info, &valid, sizeof(valid)))
+		return -EINVAL;
+
+	kvm_make_request(KVM_REQ_EXIT, vcpu);
+	kvm_vcpu_kick(vcpu);
+
+	return 0;
+}
+
 long kvm_arch_vcpu_ioctl(struct file *filp,
 			 unsigned int ioctl, unsigned long arg)
 {
@@ -3341,6 +3356,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = kvm_set_guest_paused(vcpu);
 		goto out;
 	}
+	case KVM_USER_EXIT: {
+		struct kvm_user_exit info;
+
+		r = -EFAULT;
+		if (copy_from_user(&info, argp, sizeof(info)))
+			goto out;
+		r = kvm_vcpu_ioctl_user_exit(vcpu, &info);
+		break;
+	}
 	default:
 		r = -EINVAL;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d996a7cdb4d2..bc5a1abe9626 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 +1009,10 @@ struct kvm_device_attr {
 	__u64	addr;		/* userspace address of attr data */
 };
 
+struct kvm_user_exit {
+	__u8 reserved[32];
+};
+
 #define  KVM_DEV_VFIO_GROUP			1
 #define   KVM_DEV_VFIO_GROUP_ADD			1
 #define   KVM_DEV_VFIO_GROUP_DEL			2
@@ -1119,6 +1124,8 @@ 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..d7ffe6090520 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2248,15 +2248,16 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
 		return -EINVAL;
 
-#if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
 	/*
 	 * Special cases: vcpu ioctls that are asynchronous to vcpu execution,
 	 * so vcpu_load() would break it.
 	 */
+#if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
 	if (ioctl == KVM_S390_INTERRUPT || ioctl == KVM_S390_IRQ || ioctl == KVM_INTERRUPT)
 		return kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 #endif
-
+	if (ioctl == KVM_USER_EXIT)
+		return kvm_arch_vcpu_ioctl(filp, ioctl, arg);
 
 	r = vcpu_load(vcpu);
 	if (r)
-- 
2.5.0