[PATCH v4 1/6] kvm: add device control API

Scott Wood
2013-04-13T00:08:42Z

Currently, devices that are emulated inside KVM are configured in a
hardcoded manner based on an assumption that any given architecture
only has one way to do it. If there's any need to access device state,
it is done through inflexible one-purpose-only IOCTLs (e.g.
KVM_GET/SET_LAPIC). Defining new IOCTLs for every little thing is
cumbersome and depletes a limited numberspace.

This API provides a mechanism to instantiate a device of a certain
type, returning an ID that can be used to set/get attributes of the
device. Attributes may include configuration parameters (e.g.
register base address), device state, operational commands, etc. It
is similar to the ONE_REG API, except that it acts on devices rather
than vcpus.

Both device types and individual attributes can be tested without having
to create the device or get/set the attribute, without the need for
separately managing enumerated capabilities.

Signed-off-by: Scott Wood <scottwood@freescale.com>
---
v4:
- Move some boilerplate back into generic code, as requested by Gleb.
File descriptor management and reference counting is no longer the
concern of the device implementation.

- Don't hold kvm->lock during create. The original reasons
for doing so have vanished as for as MPIC is concerned, and
this avoids needing to answer the question of whether to
hold the lock during destroy as well.

Paul, you may need to acquire the lock yourself in kvm_create_xics()
to protect the -EEXIST check.

v3: remove some changes that were merged into this patch by accident,
and fix the error documentation for KVM_CREATE_DEVICE.
---
Documentation/virtual/kvm/api.txt | 70 ++++++++++++++++
Documentation/virtual/kvm/devices/README | 1 +
include/linux/kvm_host.h | 35 ++++++++
include/uapi/linux/kvm.h | 27 +++++++
virt/kvm/kvm_main.c | 129 ++++++++++++++++++++++++++++++
5 files changed, 262 insertions(+)
create mode 100644 Documentation/virtual/kvm/devices/README

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 976eb65..d52f3f9 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2173,6 +2173,76 @@ header; first `n_valid' valid entries with contents from the data
written, then `n_invalid' invalid entries, invalidating any previously
valid entries found.

+4.79 KVM_CREATE_DEVICE
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: vm ioctl
+Parameters: struct kvm_create_device (in/out)
+Returns: 0 on success, -1 on error
+Errors:
+ ENODEV: The device type is unknown or unsupported
+ EEXIST: Device already created, and this type of device may not
+ be instantiated multiple times
+
+ Other error conditions may be defined by individual device types or
+ have their standard meanings.
+
+Creates an emulated device in the kernel. The file descriptor returned
+in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR.
+
+If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the
+device type is supported (not necessarily whether it can be created
+in the current vm).
+
+Individual devices should not define flags. Attributes should be used
+for specifying any behavior that is not implied by the device type
+number.
+
+struct kvm_create_device {
+ __u32 type; /* in: KVM_DEV_TYPE_xxx */
+ __u32 fd; /* out: device handle */
+ __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */
+};
+
+4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+ EPERM: The attribute cannot (currently) be accessed this way
+ (e.g. read-only attribute, or attribute that only makes
+ sense when the device is in a different state)
+
+ Other error conditions may be defined by individual device types.
+
+Gets/sets a specified piece of device configuration and/or state. The
+semantics are device-specific. See individual device documentation in
+the "devices" directory. As with ONE_REG, the size of the data
+transferred is defined by the particular attribute.
+
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
+4.81 KVM_HAS_DEVICE_ATTR
+
+Capability: KVM_CAP_DEVICE_CTRL
+Type: device ioctl
+Parameters: struct kvm_device_attr
+Returns: 0 on success, -1 on error
+Errors:
+ ENXIO: The group or attribute is unknown/unsupported for this device
+
+Tests whether a device supports a particular attribute. A successful
+return indicates the attribute is implemented. It does not necessarily
+indicate that the attribute can be read or written in the device's
+current state. "addr" is ignored.

4.77 KVM_ARM_VCPU_INIT

diff --git a/Documentation/virtual/kvm/devices/README b/Documentation/virtual/kvm/devices/README
new file mode 100644
index 0000000..34a6983
--- /dev/null
+++ b/Documentation/virtual/kvm/devices/README
@@ -0,0 +1 @@
+This directory contains specific device bindings for KVM_CAP_DEVICE_CTRL.
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 20d77d2..8fce9bc 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1063,6 +1063,41 @@ static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)

extern bool kvm_rebooting;

+struct kvm_device_ops;
+
+struct kvm_device {
+ struct kvm_device_ops *ops;
+ struct kvm *kvm;
+ atomic_t users;
+ void *private;
+};
+
+/* create, destroy, and name are mandatory */
+struct kvm_device_ops {
+ const char *name;
+ int (*create)(struct kvm_device *dev, u32 type);
+
+ /*
+ * Destroy is responsible for freeing dev.
+ *
+ * Destroy may be called before or after destructors are called
+ * on emulated I/O regions, depending on whether a reference is
+ * held by a vcpu or other kvm component that gets destroyed
+ * after the emulated I/O.
+ */
+ void (*destroy)(struct kvm_device *dev);
+
+ int (*set_attr)(struct kvm_device *dev, struct kvm_device_attr *attr);
+ int (*get_attr)(struct kvm_device *dev, struct kvm_device_attr *attr);
+ int (*has_attr)(struct kvm_device *dev, struct kvm_device_attr *attr);
+ long (*ioctl)(struct kvm_device *dev, unsigned int ioctl,
+ unsigned long arg);
+};
+
+void kvm_device_get(struct kvm_device *dev);
+void kvm_device_put(struct kvm_device *dev);
+struct kvm_device *kvm_device_from_filp(struct file *filp);
+
#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT

static inline void kvm_vcpu_set_in_spin_loop(struct kvm_vcpu *vcpu, bool val)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 74d0ff3..20ce2d2 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -668,6 +668,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_PPC_EPR 86
#define KVM_CAP_ARM_PSCI 87
#define KVM_CAP_ARM_SET_DEVICE_ADDR 88
+#define KVM_CAP_DEVICE_CTRL 89

#ifdef KVM_CAP_IRQ_ROUTING

@@ -909,6 +910,32 @@ struct kvm_s390_ucas_mapping {
#define KVM_ARM_SET_DEVICE_ADDR _IOW(KVMIO, 0xab, struct kvm_arm_device_addr)

/*
+ * Device control API, available with KVM_CAP_DEVICE_CTRL
+ */
+#define KVM_CREATE_DEVICE_TEST 1
+
+struct kvm_create_device {
+ __u32 type; /* in: KVM_DEV_TYPE_xxx */
+ __u32 fd; /* out: device handle */
+ __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */
+};
+
+struct kvm_device_attr {
+ __u32 flags; /* no flags currently defined */
+ __u32 group; /* device-defined */
+ __u64 attr; /* group-defined */
+ __u64 addr; /* userspace address of attr data */
+};
+
+/* ioctl for vm fd */
+#define KVM_CREATE_DEVICE _IOWR(KVMIO, 0xe0, struct kvm_create_device)
+
+/* ioctls for fds returned by KVM_CREATE_DEVICE */
+#define KVM_SET_DEVICE_ATTR _IOW(KVMIO, 0xe1, struct kvm_device_attr)
+#define KVM_GET_DEVICE_ATTR _IOW(KVMIO, 0xe2, struct kvm_device_attr)
+#define KVM_HAS_DEVICE_ATTR _IOW(KVMIO, 0xe3, struct kvm_device_attr)
+
+/*
* ioctls for vcpu fds
*/
#define KVM_RUN _IO(KVMIO, 0x80)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5cc53c9..e2b18af 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2158,6 +2158,117 @@ out:
}
#endif

+static int kvm_device_ioctl_attr(struct kvm_device *dev,
+ int (*accessor)(struct kvm_device *dev,
+ struct kvm_device_attr *attr),
+ unsigned long arg)
+{
+ struct kvm_device_attr attr;
+
+ if (!accessor)
+ return -EPERM;
+
+ if (copy_from_user(&attr, (void __user *)arg, sizeof(attr)))
+ return -EFAULT;
+
+ return accessor(dev, &attr);
+}
+
+static long kvm_device_ioctl(struct file *filp, unsigned int ioctl,
+ unsigned long arg)
+{
+ struct kvm_device *dev = filp->private_data;
+
+ switch (ioctl) {
+ case KVM_SET_DEVICE_ATTR:
+ return kvm_device_ioctl_attr(dev, dev->ops->set_attr, arg);
+ case KVM_GET_DEVICE_ATTR:
+ return kvm_device_ioctl_attr(dev, dev->ops->get_attr, arg);
+ case KVM_HAS_DEVICE_ATTR:
+ return kvm_device_ioctl_attr(dev, dev->ops->has_attr, arg);
+ default:
+ if (dev->ops->ioctl)
+ return dev->ops->ioctl(dev, ioctl, arg);
+
+ return -ENOTTY;
+ }
+}
+
+void kvm_device_get(struct kvm_device *dev)
+{
+ atomic_inc(&dev->users);
+}
+
+void kvm_device_put(struct kvm_device *dev)
+{
+ if (atomic_dec_and_test(&dev->users))
+ dev->ops->destroy(dev);
+}
+
+static int kvm_device_release(struct inode *inode, struct file *filp)
+{
+ struct kvm_device *dev = filp->private_data;
+ struct kvm *kvm = dev->kvm;
+
+ kvm_device_put(dev);
+ kvm_put_kvm(kvm);
+ return 0;
+}
+
+static const struct file_operations kvm_device_fops = {
+ .unlocked_ioctl = kvm_device_ioctl,
+ .release = kvm_device_release,
+};
+
+struct kvm_device *kvm_device_from_filp(struct file *filp)
+{
+ if (filp->f_op != &kvm_device_fops)
+ return NULL;
+
+ return filp->private_data;
+}
+
+static int kvm_ioctl_create_device(struct kvm *kvm,
+ struct kvm_create_device *cd)
+{
+ struct kvm_device_ops *ops = NULL;
+ struct kvm_device *dev;
+ bool test = cd->flags & KVM_CREATE_DEVICE_TEST;
+ int ret;
+
+ switch (cd->type) {
+ default:
+ return -ENODEV;
+ }
+
+ if (test)
+ return 0;
+
+ dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+ if (!dev)
+ return -ENOMEM;
+
+ dev->ops = ops;
+ dev->kvm = kvm;
+ atomic_set(&dev->users, 1);
+
+ ret = ops->create(dev, cd->type);
+ if (ret < 0) {
+ kfree(dev);
+ return ret;
+ }
+
+ ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR);
+ if (ret < 0) {
+ ops->destroy(dev);
+ return ret;
+ }
+
+ kvm_get_kvm(kvm);
+ cd->fd = ret;
+ return 0;
+}
+
static long kvm_vm_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
@@ -2272,6 +2383,24 @@ static long kvm_vm_ioctl(struct file *filp,
break;
}
#endif
+ case KVM_CREATE_DEVICE: {
+ struct kvm_create_device cd;
+
+ r = -EFAULT;
+ if (copy_from_user(&cd, argp, sizeof(cd)))
+ goto out;
+
+ r = kvm_ioctl_create_device(kvm, &cd);
+ if (r)
+ goto out;
+
+ r = -EFAULT;
+ if (copy_to_user(argp, &cd, sizeof(cd)))
+ goto out;
+
+ r = 0;
+ break;
+ }
default:
r = kvm_arch_vm_ioctl(filp, ioctl, arg);
if (r == -ENOTTY)
--
1.7.10.4