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diff --git a/Documentation/virt/kvm/arm/psci.rst b/Documentation/virt/kvm/arm/psci.rst new file mode 100644 index 000000000000..d52c2e83b5b8 --- /dev/null +++ b/Documentation/virt/kvm/arm/psci.rst @@ -0,0 +1,77 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================= +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: + +* 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 |