1KVM implements the PSCI (Power State Coordination Interface)
2specification in order to provide services such as CPU on/off, reset
3and power-off to the guest.
4
5The PSCI specification is regularly updated to provide new features,
6and KVM implements these updates if they make sense from a virtualization
7point of view.
8
9This means that a guest booted on two different versions of KVM can
10observe two different "firmware" revisions. This could cause issues if
11a given guest is tied to a particular PSCI revision (unlikely), or if
12a migration causes a different PSCI version to be exposed out of the
13blue to an unsuspecting guest.
14
15In order to remedy this situation, KVM exposes a set of "firmware
16pseudo-registers" that can be manipulated using the GET/SET_ONE_REG
17interface. These registers can be saved/restored by userspace, and set
18to a convenient value if required.
19
20The following register is defined:
21
22* KVM_REG_ARM_PSCI_VERSION:
23
24  - Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set
25    (and thus has already been initialized)
26  - Returns the current PSCI version on GET_ONE_REG (defaulting to the
27    highest PSCI version implemented by KVM and compatible with v0.2)
28  - Allows any PSCI version implemented by KVM and compatible with
29    v0.2 to be set with SET_ONE_REG
30  - Affects the whole VM (even if the register view is per-vcpu)
31