On 27/08/2019 09:44, Christoffer Dall wrote: > On Wed, Aug 21, 2019 at 04:36:47PM +0100, Steven Price wrote: >> 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: >> + > > I feel it would be more consistent to have the details of this in > Documentation/virt/kvm/devices/arm-pv-time.txt and refer to this > document from here. Fair point - I'll move this lower part of the document and add a reference. Thanks, Steve >> + 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 >> > > Thanks, > > Christoffer >
