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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