Re: [RFC PATCH v3 1/6] kvm: add device control API

Alexander Graf
2013-04-03T15:13:13Z

On 03.04.2013, at 03:57, 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>
> ---
> v3: remove some changes that were merged into this patch by accident,
> and fix the error documentation for KVM_CREATE_DEVICE.
>
> NOTE: I had some difficulty figuring out what ioctl numbers I should
> assign... it seems that at one point care was taken to keep vcpu and
> vm ioctls separate, but some overlap exists now (despite not exhausing
> the ioctl space). Some of that was my fault, but not all of it. :-)
> I moved to a new ioctl range for device control -- please let me know
> if there's something else you'd prefer I do.
> ---
> Documentation/virtual/kvm/api.txt | 70 ++++++++++++++++++++++++++++++
> Documentation/virtual/kvm/devices/README | 1 +
> include/uapi/linux/kvm.h | 27 ++++++++++++
> virt/kvm/kvm_main.c | 31 +++++++++++++
> 4 files changed, 129 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/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 these above the ioctl number definitions, where all the other structs already are.

Alex