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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:
* KVM_REG_ARM_PSCI_VERSION:
- 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)
* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
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 [1].
Accepted values are:
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL: KVM does not offer
firmware support for the workaround. The mitigation status for the
guest is unknown.
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL: The workaround HVC call is
available to the guest and required for the mitigation.
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED: The workaround HVC call
is available to the guest, but it is not needed on this VCPU.
* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
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:
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL: A workaround is not
available. KVM does not offer firmware support for the workaround.
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN: The workaround state is
unknown. KVM does not offer firmware support for the workaround.
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL: 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.
KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED: The workaround is
always active on this vCPU or it is not needed.
[1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf
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