[PATCH v12 36/77] KVM: introspection: add KVM_INTROSPECTION_PREUNHOOK

["Adalbert Lazăr" <alazar@bitdefender.com>]

In certain situations (when the guest has to be paused, suspended,
migrated, etc.), the device manager will use this new ioctl in order to
trigger the KVMI_VM_EVENT_UNHOOK event. If the event is sent successfully
(the VM has an active introspection channel), the device manager should
delay the action (pause/suspend/...) to give the introspection tool the
chance to remove its hooks (eg. breakpoints) while the guest is still
running. Once a timeout is reached or the introspection tool has closed
the socket, the device manager should resume the action.

Signed-off-by: Adalbert Lazăr <alazar@bitdefender.com>
---
 Documentation/virt/kvm/api.rst    | 28 ++++++++++++++++++++++++++++
 Documentation/virt/kvm/kvmi.rst   |  7 ++++---
 include/linux/kvmi_host.h         |  1 +
 include/uapi/linux/kvm.h          |  2 ++
 virt/kvm/introspection/kvmi.c     | 30 ++++++++++++++++++++++++++++++
 virt/kvm/introspection/kvmi_int.h |  1 +
 virt/kvm/introspection/kvmi_msg.c |  5 +++++
 virt/kvm/kvm_main.c               |  5 +++++
 8 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 85f02eda4895..abb289883542 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5594,6 +5594,34 @@ the event is disallowed.
 Unless set to -1 (meaning all events), id must be a event ID
 (e.g. KVMI_VM_EVENT_UNHOOK, KVMI_VCPU_EVENT_CR, etc.)
 
+4.131 KVM_INTROSPECTION_PREUNHOOK
+---------------------------------
+
+:Capability: KVM_CAP_INTROSPECTION
+:Architectures: x86
+:Type: vm ioctl
+:Parameters: none
+:Returns: 0 on success, a negative value on error
+
+Errors:
+
+  ======     ============================================================
+  EFAULT     the VM is not introspected yet (use KVM_INTROSPECTION_HOOK)
+  ENOENT     the socket (passed with KVM_INTROSPECTION_HOOK) had an error
+  ENOENT     the introspection tool didn't subscribed
+             to this type of introspection event (unhook)
+  ======     ============================================================
+
+This ioctl is used to inform that the current VM is
+paused/suspended/migrated/etc.
+
+KVM should send an 'unhook' introspection event to the introspection tool.
+
+If this ioctl is successful, the userspace should give the
+introspection tool a chance to unhook the VM and then it should use
+KVM_INTROSPECTION_UNHOOK to make sure all the introspection structures
+are freed.
+
 5. The kvm_run structure
 ========================
 
diff --git a/Documentation/virt/kvm/kvmi.rst b/Documentation/virt/kvm/kvmi.rst
index 6f8583d4aeb2..33490bc9d1c1 100644
--- a/Documentation/virt/kvm/kvmi.rst
+++ b/Documentation/virt/kvm/kvmi.rst
@@ -183,9 +183,10 @@ becomes necessary to remove them before the guest is suspended, moved
 (migrated) or a snapshot with memory is created.
 
 The actions are normally performed by the device manager. In the case
-of QEMU, it will use another ioctl to notify the introspection tool and
-wait for a limited amount of time (a few seconds) for a confirmation that
-is OK to proceed (the introspection tool will close the connection).
+of QEMU, it will use the *KVM_INTROSPECTION_PREUNHOOK* ioctl to trigger
+the *KVMI_VM_EVENT_UNHOOK* event and wait for a limited amount of time (a
+few seconds) for a confirmation that is OK to proceed. The introspection
+tool will close the connection to signal this.
 
 Live migrations
 ---------------
diff --git a/include/linux/kvmi_host.h b/include/linux/kvmi_host.h
index a5ede07686b9..81eac9f53a3f 100644
--- a/include/linux/kvmi_host.h
+++ b/include/linux/kvmi_host.h
@@ -32,6 +32,7 @@ int kvmi_ioctl_command(struct kvm *kvm,
 		       const struct kvm_introspection_feature *feat);
 int kvmi_ioctl_event(struct kvm *kvm,
 		     const struct kvm_introspection_feature *feat);
+int kvmi_ioctl_preunhook(struct kvm *kvm);
 
 #else
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index c56f40c47890..160c7ba1c666 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1834,6 +1834,8 @@ struct kvm_introspection_feature {
 #define KVM_INTROSPECTION_COMMAND _IOW(KVMIO, 0xca, struct kvm_introspection_feature)
 #define KVM_INTROSPECTION_EVENT   _IOW(KVMIO, 0xcb, struct kvm_introspection_feature)
 
+#define KVM_INTROSPECTION_PREUNHOOK  _IO(KVMIO, 0xcc)
+
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
 #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)
diff --git a/virt/kvm/introspection/kvmi.c b/virt/kvm/introspection/kvmi.c
index e39fe4721243..a527795f01a4 100644
--- a/virt/kvm/introspection/kvmi.c
+++ b/virt/kvm/introspection/kvmi.c
@@ -384,3 +384,33 @@ int kvmi_ioctl_command(struct kvm *kvm,
 	mutex_unlock(&kvm->kvmi_lock);
 	return err;
 }
+
+static bool kvmi_unhook_event(struct kvm_introspection *kvmi)
+{
+	int err;
+
+	err = kvmi_msg_send_unhook(kvmi);
+
+	return !err;
+}
+
+int kvmi_ioctl_preunhook(struct kvm *kvm)
+{
+	struct kvm_introspection *kvmi;
+	int err = 0;
+
+	mutex_lock(&kvm->kvmi_lock);
+
+	kvmi = KVMI(kvm);
+	if (!kvmi) {
+		err = -EFAULT;
+		goto out;
+	}
+
+	if (!kvmi_unhook_event(kvmi))
+		err = -ENOENT;
+
+out:
+	mutex_unlock(&kvm->kvmi_lock);
+	return err;
+}
diff --git a/virt/kvm/introspection/kvmi_int.h b/virt/kvm/introspection/kvmi_int.h
index 1e1d1fad4035..ef4850e8bfae 100644
--- a/virt/kvm/introspection/kvmi_int.h
+++ b/virt/kvm/introspection/kvmi_int.h
@@ -18,6 +18,7 @@ bool kvmi_sock_get(struct kvm_introspection *kvmi, int fd);
 void kvmi_sock_shutdown(struct kvm_introspection *kvmi);
 void kvmi_sock_put(struct kvm_introspection *kvmi);
 bool kvmi_msg_process(struct kvm_introspection *kvmi);
+int kvmi_msg_send_unhook(struct kvm_introspection *kvmi);
 
 /* kvmi.c */
 void *kvmi_msg_alloc(void);
diff --git a/virt/kvm/introspection/kvmi_msg.c b/virt/kvm/introspection/kvmi_msg.c
index 795495340dc0..09321380629f 100644
--- a/virt/kvm/introspection/kvmi_msg.c
+++ b/virt/kvm/introspection/kvmi_msg.c
@@ -260,3 +260,8 @@ bool kvmi_msg_process(struct kvm_introspection *kvmi)
 out:
 	return err == 0;
 }
+
+int kvmi_msg_send_unhook(struct kvm_introspection *kvmi)
+{
+	return -1;
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 77102be42475..b0a23fcb935c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4580,6 +4580,11 @@ static long kvm_vm_ioctl(struct file *filp,
 			r = kvmi_ioctl_command(kvm, &feat);
 		break;
 	}
+	case KVM_INTROSPECTION_PREUNHOOK:
+		r = -EPERM;
+		if (enable_introspection)
+			r = kvmi_ioctl_preunhook(kvm);
+		break;
 #endif /* CONFIG_KVM_INTROSPECTION */
 	default:
 		r = kvm_arch_vm_ioctl(filp, ioctl, arg);