On 03/10/2019 13:19, Andrew Jones wrote: > On Wed, Oct 02, 2019 at 03:50:28PM +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 | 65 +++++++++++++++++++++++++ >> Documentation/virt/kvm/devices/vcpu.txt | 14 ++++++ >> 2 files changed, 79 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..fa15c12eec91 >> --- /dev/null >> +++ b/Documentation/virt/kvm/arm/pvtime.txt > > Maybe use .rst instead of .txt? Fair point - I guess .rst is the way of the future! >> @@ -0,0 +1,65 @@ >> +Paravirtualized time support for arm64 >> +====================================== >> + >> +Arm specification DEN0057/A defined a standard for paravirtualised time > > s/defined/defines/ ? > >> +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 > > The spec calls this PV_TIME_FEATURES. > >> +PV_TIME_ST 0xC5000022 > > This is 0xC5000021 in the spec. This is somewhat embarrassing. Apparently when I was reviewing the new specification I didn't notice these (subtle) changes. Thanks for pointing it out to me! I'll update the code to match. >> + >> +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) : The function to query for support. >> + Currently only PV_TIME_ST is supported. > > The spec calls this PV_call_id, but maybe PV_func_id would have been better. I guess they are generally called "hypercalls" not "hyperfunctions" - so I'll match the spec here. >> + Return value: (int32) : NOT_SUPPORTED (-1) or SUCCESS (0) if the relevant >> + PV-time feature is supported by the hypervisor. > > This is an int64 in the spec. True - although the values easily fit in int32 too! But I'll update to be consistent with the spec. >> + >> +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 > > The spec version is 1.0 and Table 1 says "For implementations compliant > with this revision of the specification...". So I think this description > should be "Must be 0 for version 1.0". Will update. Thanks, Steve >> + 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. >> + >> +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 >> > > Thanks, > drew >
