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

Alexander Graf
2013-04-25T13:45:14Z

On 25.04.2013, at 14:07, Gleb Natapov wrote:

> On Thu, Apr 25, 2013 at 12:47:39PM +0200, Alexander Graf wrote:
>>
>> On 25.04.2013, at 11:43, Gleb Natapov wrote:
>>
>>> On Fri, Apr 12, 2013 at 07:08:42PM -0500, Scott Wood wrote:
>>>> 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 */
>>>> +};
>>> Should we add __u32 padding here to make struct size multiple of u64?
>>
>> Do you know of any arch that pads structs to u64 boundaries? x86_64 doesn't and ppc64 doesn't either.
>>
> Not really. I just notices that we pad some structures to that effect.

I don't think we really need to :).

>
>>>
>>>> +
>>>> +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 */
>>>> +};
>>> Please move struct definitions and KVM_CREATE_DEVICE_TEST define out
>>> from ioctl definition block.
>>
>> Let me change that in my tree...
>>
> So are you sending this via your tree and I should not apply it directly?

I was hoping to have things ready very soon for you to just pull...

Alex