Power State Coordination Interface (PSCI)¶
KVM implements the PSCI (Power State Coordination Interface) specification in order to provide services such as CPU on/off, reset and power-off to the guest.
The PSCI specification is regularly updated to provide new features, and KVM implements these updates if they make sense from a virtualization point of view.
This means that a guest booted on two different versions of KVM can observe two different “firmware” revisions. This could cause issues if a given guest is tied to a particular PSCI revision (unlikely), or if a migration causes a different PSCI version to be exposed out of the blue to an unsuspecting guest.
In order to remedy this situation, KVM exposes a set of “firmware pseudo-registers” that can be manipulated using the GET/SET_ONE_REG interface. These registers can be saved/restored by userspace, and set to a convenient value if required.
The following register is defined:
Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set (and thus has already been initialized)
Returns the current PSCI version on GET_ONE_REG (defaulting to the highest PSCI version implemented by KVM and compatible with v0.2)
Allows any PSCI version implemented by KVM and compatible with v0.2 to be set with SET_ONE_REG
Affects the whole VM (even if the register view is per-vcpu)
Holds the state of the firmware support to mitigate CVE-2017-5715, as offered by KVM to the guest via a HVC call. The workaround is described under SMCCC_ARCH_WORKAROUND_1 in .
Accepted values are:
KVM does not offer firmware support for the workaround. The mitigation status for the guest is unknown.
The workaround HVC call is available to the guest and required for the mitigation.
The workaround HVC call is available to the guest, but it is not needed on this VCPU.
Holds the state of the firmware support to mitigate CVE-2018-3639, as offered by KVM to the guest via a HVC call. The workaround is described under SMCCC_ARCH_WORKAROUND_2 in 1.
Accepted values are:
A workaround is not available. KVM does not offer firmware support for the workaround.
The workaround state is unknown. KVM does not offer firmware support for the workaround.
The workaround is available, and can be disabled by a vCPU. If KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED is set, it is active for this vCPU.
The workaround is always active on this vCPU or it is not needed.