1.. SPDX-License-Identifier: GPL-2.0 2 3======================= 4ARM Hypercall Interface 5======================= 6 7KVM handles the hypercall services as requested by the guests. New hypercall 8services are regularly made available by the ARM specification or by KVM (as 9vendor services) if they make sense from a virtualization point of view. 10 11This means that a guest booted on two different versions of KVM can observe 12two different "firmware" revisions. This could cause issues if a given guest 13is tied to a particular version of a hypercall service, or if a migration 14causes a different version to be exposed out of the blue to an unsuspecting 15guest. 16 17In order to remedy this situation, KVM exposes a set of "firmware 18pseudo-registers" that can be manipulated using the GET/SET_ONE_REG 19interface. These registers can be saved/restored by userspace, and set 20to a convenient value as required. 21 22The following registers are defined: 23 24* KVM_REG_ARM_PSCI_VERSION: 25 26 KVM implements the PSCI (Power State Coordination Interface) 27 specification in order to provide services such as CPU on/off, reset 28 and power-off to the guest. 29 30 - Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set 31 (and thus has already been initialized) 32 - Returns the current PSCI version on GET_ONE_REG (defaulting to the 33 highest PSCI version implemented by KVM and compatible with v0.2) 34 - Allows any PSCI version implemented by KVM and compatible with 35 v0.2 to be set with SET_ONE_REG 36 - Affects the whole VM (even if the register view is per-vcpu) 37 38* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1: 39 Holds the state of the firmware support to mitigate CVE-2017-5715, as 40 offered by KVM to the guest via a HVC call. The workaround is described 41 under SMCCC_ARCH_WORKAROUND_1 in [1]. 42 43 Accepted values are: 44 45 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL: 46 KVM does not offer 47 firmware support for the workaround. The mitigation status for the 48 guest is unknown. 49 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL: 50 The workaround HVC call is 51 available to the guest and required for the mitigation. 52 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED: 53 The workaround HVC call 54 is available to the guest, but it is not needed on this VCPU. 55 56* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2: 57 Holds the state of the firmware support to mitigate CVE-2018-3639, as 58 offered by KVM to the guest via a HVC call. The workaround is described 59 under SMCCC_ARCH_WORKAROUND_2 in [1]_. 60 61 Accepted values are: 62 63 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL: 64 A workaround is not 65 available. KVM does not offer firmware support for the workaround. 66 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN: 67 The workaround state is 68 unknown. KVM does not offer firmware support for the workaround. 69 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL: 70 The workaround is available, 71 and can be disabled by a vCPU. If 72 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED is set, it is active for 73 this vCPU. 74 KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED: 75 The workaround is always active on this vCPU or it is not needed. 76 77 78Bitmap Feature Firmware Registers 79--------------------------------- 80 81Contrary to the above registers, the following registers exposes the 82hypercall services in the form of a feature-bitmap to the userspace. This 83bitmap is translated to the services that are available to the guest. 84There is a register defined per service call owner and can be accessed via 85GET/SET_ONE_REG interface. 86 87By default, these registers are set with the upper limit of the features 88that are supported. This way userspace can discover all the usable 89hypercall services via GET_ONE_REG. The user-space can write-back the 90desired bitmap back via SET_ONE_REG. The features for the registers that 91are untouched, probably because userspace isn't aware of them, will be 92exposed as is to the guest. 93 94Note that KVM will not allow the userspace to configure the registers 95anymore once any of the vCPUs has run at least once. Instead, it will 96return a -EBUSY. 97 98The pseudo-firmware bitmap register are as follows: 99 100* KVM_REG_ARM_STD_BMAP: 101 Controls the bitmap of the ARM Standard Secure Service Calls. 102 103 The following bits are accepted: 104 105 Bit-0: KVM_REG_ARM_STD_BIT_TRNG_V1_0: 106 The bit represents the services offered under v1.0 of ARM True Random 107 Number Generator (TRNG) specification, ARM DEN0098. 108 109* KVM_REG_ARM_STD_HYP_BMAP: 110 Controls the bitmap of the ARM Standard Hypervisor Service Calls. 111 112 The following bits are accepted: 113 114 Bit-0: KVM_REG_ARM_STD_HYP_BIT_PV_TIME: 115 The bit represents the Paravirtualized Time service as represented by 116 ARM DEN0057A. 117 118* KVM_REG_ARM_VENDOR_HYP_BMAP: 119 Controls the bitmap of the Vendor specific Hypervisor Service Calls. 120 121 The following bits are accepted: 122 123 Bit-0: KVM_REG_ARM_VENDOR_HYP_BIT_FUNC_FEAT 124 The bit represents the ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID 125 and ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID function-ids. 126 127 Bit-1: KVM_REG_ARM_VENDOR_HYP_BIT_PTP: 128 The bit represents the Precision Time Protocol KVM service. 129 130Errors: 131 132 ======= ============================================================= 133 -ENOENT Unknown register accessed. 134 -EBUSY Attempt a 'write' to the register after the VM has started. 135 -EINVAL Invalid bitmap written to the register. 136 ======= ============================================================= 137 138.. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf 139