On Fri, Aug 30, 2019 at 09:42:46AM +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 | 64 +++++++++++++++++++++++++ > Documentation/virt/kvm/devices/vcpu.txt | 14 ++++++ > 2 files changed, 78 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..dda3f0f855b9 > --- /dev/null > +++ b/Documentation/virt/kvm/arm/pvtime.txt > @@ -0,0 +1,64 @@ > +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 PV_TIME_LPT doesn't exist > + 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 > + 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 0.1 > + Attributes | 4 | 4 | Must be 0 The above fields don't appear to be exposed to userspace in anyway. How will we handle migration from one KVM with one version of the structure to another? > + 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. Should we provide a recommendation as to how that reserved memory is provided? One memslot divided into NR_VCPUS subregions? Should the reserved region be described to the guest kernel with DT/ACPI? Or should userspace ensure the region is not within any DT/ACPI described regions? > + > +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..896777f76f36 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_SET_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 > Thanks, drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
