From: Steven Price <steven.price@xxxxxxx> 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> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> --- Documentation/virt/kvm/arm/pvtime.rst | 80 +++++++++++++++++++++++++ Documentation/virt/kvm/devices/vcpu.txt | 14 +++++ 2 files changed, 94 insertions(+) create mode 100644 Documentation/virt/kvm/arm/pvtime.rst diff --git a/Documentation/virt/kvm/arm/pvtime.rst b/Documentation/virt/kvm/arm/pvtime.rst new file mode 100644 index 000000000000..2357dd2d8655 --- /dev/null +++ b/Documentation/virt/kvm/arm/pvtime.rst @@ -0,0 +1,80 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Paravirtualized time support for arm64 +====================================== + +Arm specification DEN0057/A defines 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_TIME_FEATURES: 0xC5000020 +* PV_TIME_ST: 0xC5000021 + +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_TIME_FEATURES + ============= ======== ========== + Function ID: (uint32) 0xC5000020 + PV_call_id: (uint32) The function to query for support. + Currently only PV_TIME_ST is supported. + Return value: (int64) NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant + PV-time feature is supported by the hypervisor. + ============= ======== ========== + +PV_TIME_ST + ============= ======== ========== + Function ID: (uint32) 0xC5000021 + Return value: (int64) IPA of the stolen time data structure for this + VCPU. 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 1.0 | ++-------------+-------------+-------------+----------------------------+ +| 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. | ++-------------+-------------+-------------+----------------------------+ + +All values in the structure are stored little-endian. + +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. + +It is advisable that one or more 64k pages are set aside for the purpose of +these structures and not used for other purposes, this enables the guest to map +the region using 64k pages and avoids conflicting attributes with other memory. + +For the user space interface see Documentation/virt/kvm/devices/vcpu.txt +section "3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL". diff --git a/Documentation/virt/kvm/devices/vcpu.txt b/Documentation/virt/kvm/devices/vcpu.txt index 2b5dab16c4f2..6f3bd64a05b0 100644 --- a/Documentation/virt/kvm/devices/vcpu.txt +++ b/Documentation/virt/kvm/devices/vcpu.txt @@ -60,3 +60,17 @@ time to use the number provided for a given timer, overwriting any previously configured values on other VCPUs. Userspace should configure the interrupt numbers on at least one VCPU after creating all VCPUs and before running any VCPUs. + +3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL +Architectures: ARM64 + +3.1 ATTRIBUTE: KVM_ARM_VCPU_PVTIME_IPA +Parameters: 64-bit base address +Returns: -ENXIO: Stolen time not implemented + -EEXIST: Base address already set for this VCPU + -EINVAL: Base address not 64 byte aligned + +Specifies the base address of the stolen time structure for this VCPU. The +base address must be 64 byte aligned and exist within a valid guest memory +region. See Documentation/virt/kvm/arm/pvtime.txt for more information +including the layout of the stolen time structure. -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
