Introduce a paravirtualization interface for KVM/arm64 based on the "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A. This only adds the details about "Stolen Time" as the details of "Live Physical Time" have not been fully agreed. User space can specify a reserved area of memory for the guest and inform KVM to populate the memory with information on time that the host kernel has stolen from the guest. A hypercall interface is provided for the guest to interrogate the hypervisor's support for this interface and the location of the shared memory structures. Signed-off-by: Steven Price <steven.price@xxxxxxx> --- Documentation/virt/kvm/arm/pvtime.txt | 100 ++++++++++++++++++++++++++ 1 file changed, 100 insertions(+) create mode 100644 Documentation/virt/kvm/arm/pvtime.txt diff --git a/Documentation/virt/kvm/arm/pvtime.txt b/Documentation/virt/kvm/arm/pvtime.txt new file mode 100644 index 000000000000..1ceb118694e7 --- /dev/null +++ b/Documentation/virt/kvm/arm/pvtime.txt @@ -0,0 +1,100 @@ +Paravirtualized time support for arm64 +====================================== + +Arm specification DEN0057/A defined a standard for paravirtualised time +support for AArch64 guests: + +https://developer.arm.com/docs/den0057/a + +KVM/arm64 implements the stolen time part of this specification by providing +some hypervisor service calls to support a paravirtualized guest obtaining a +view of the amount of time stolen from its execution. + +Two new SMCCC compatible hypercalls are defined: + +PV_FEATURES 0xC5000020 +PV_TIME_ST 0xC5000022 + +These are only available in the SMC64/HVC64 calling convention as +paravirtualized time is not available to 32 bit Arm guests. The existence of +the PV_FEATURES hypercall should be probed using the SMCCC 1.1 ARCH_FEATURES +mechanism before calling it. + +PV_FEATURES + Function ID: (uint32) : 0xC5000020 + PV_func_id: (uint32) : Either PV_TIME_LPT or PV_TIME_ST + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant + PV-time feature is supported by the hypervisor. + +PV_TIME_ST + Function ID: (uint32) : 0xC5000022 + Return value: (int64) : IPA of the stolen time data structure for this + (V)CPU. On failure: + NOT_SUPPORTED (-1) + +The IPA returned by PV_TIME_ST should be mapped by the guest as normal memory +with inner and outer write back caching attributes, in the inner shareable +domain. A total of 16 bytes from the IPA returned are guaranteed to be +meaningfully filled by the hypervisor (see structure below). + +PV_TIME_ST returns the structure for the calling VCPU. + +Stolen Time +----------- + +The structure pointed to by the PV_TIME_ST hypercall is as follows: + + Field | Byte Length | Byte Offset | Description + ----------- | ----------- | ----------- | -------------------------- + Revision | 4 | 0 | Must be 0 for version 0.1 + Attributes | 4 | 4 | Must be 0 + Stolen time | 8 | 8 | Stolen time in unsigned + | | | nanoseconds indicating how + | | | much time this VCPU thread + | | | was involuntarily not + | | | running on a physical CPU. + +The structure will be updated by the hypervisor prior to scheduling a VCPU. It +will be present within a reserved region of the normal memory given to the +guest. The guest should not attempt to write into this memory. There is a +structure per VCPU of the guest. + +User space interface +==================== + +User space can request that KVM provide the paravirtualized time interface to +a guest by creating a KVM_DEV_TYPE_ARM_PV_TIME device, for example: + + struct kvm_create_device pvtime_device = { + .type = KVM_DEV_TYPE_ARM_PV_TIME, + .attr = 0, + .flags = 0, + }; + + pvtime_fd = ioctl(vm_fd, KVM_CREATE_DEVICE, &pvtime_device); + +Creation of the device should be done after creating the vCPUs of the virtual +machine. + +The IPA of the structures must be given to KVM. This is the base address +of an array of stolen time structures (one for each VCPU). The base address +must be page aligned. The size must be at least 64 * number of VCPUs and be a +multiple of PAGE_SIZE. + +The memory for these structures should be added to the guest in the usual +manner (e.g. using KVM_SET_USER_MEMORY_REGION). + +For example: + + struct kvm_dev_arm_st_region region = { + .gpa = <IPA of guest base address>, + .size = <size in bytes> + }; + + struct kvm_device_attr st_base = { + .group = KVM_DEV_ARM_PV_TIME_PADDR, + .attr = KVM_DEV_ARM_PV_TIME_ST, + .addr = (u64)®ion + }; + + ioctl(pvtime_fd, KVM_SET_DEVICE_ATTR, &st_base); -- 2.20.1
