.. SPDX-License-Identifier: GPL-2.0
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=========================================
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Power State Coordination Interface (PSCI)
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=========================================
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KVM implements the PSCI (Power State Coordination Interface)
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specification in order to provide services such as CPU on/off, reset
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and power-off to the guest.
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The PSCI specification is regularly updated to provide new features,
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and KVM implements these updates if they make sense from a virtualization
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point of view.
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This means that a guest booted on two different versions of KVM can
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observe two different "firmware" revisions. This could cause issues if
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a given guest is tied to a particular PSCI revision (unlikely), or if
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a migration causes a different PSCI version to be exposed out of the
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blue to an unsuspecting guest.
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In order to remedy this situation, KVM exposes a set of "firmware
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pseudo-registers" that can be manipulated using the GET/SET_ONE_REG
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interface. These registers can be saved/restored by userspace, and set
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to a convenient value if required.
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The following register is defined:
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* KVM_REG_ARM_PSCI_VERSION:
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- Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set
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(and thus has already been initialized)
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- Returns the current PSCI version on GET_ONE_REG (defaulting to the
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highest PSCI version implemented by KVM and compatible with v0.2)
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- Allows any PSCI version implemented by KVM and compatible with
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v0.2 to be set with SET_ONE_REG
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- Affects the whole VM (even if the register view is per-vcpu)
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* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
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Holds the state of the firmware support to mitigate CVE-2017-5715, as
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offered by KVM to the guest via a HVC call. The workaround is described
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under SMCCC_ARCH_WORKAROUND_1 in [1].
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Accepted values are:
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL:
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KVM does not offer
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firmware support for the workaround. The mitigation status for the
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guest is unknown.
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL:
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The workaround HVC call is
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available to the guest and required for the mitigation.
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED:
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The workaround HVC call
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is available to the guest, but it is not needed on this VCPU.
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* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
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Holds the state of the firmware support to mitigate CVE-2018-3639, as
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offered by KVM to the guest via a HVC call. The workaround is described
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under SMCCC_ARCH_WORKAROUND_2 in [1]_.
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Accepted values are:
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL:
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A workaround is not
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available. KVM does not offer firmware support for the workaround.
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN:
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The workaround state is
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unknown. KVM does not offer firmware support for the workaround.
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL:
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The workaround is available,
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and can be disabled by a vCPU. If
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED is set, it is active for
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this vCPU.
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KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED:
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The workaround is always active on this vCPU or it is not needed.
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.. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf
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