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

Radim Krčmář
2015-08-05T13:21:15Z

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 Krčmář <rkrcmar@redhat.com>
---
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