RE: [PATCH v15 0/9] Enable ptp_kvm for arm/arm64

Jianyong Wu
2020-11-23T09:27:11Z

Hi,
Ping ...
Any comments?

> -----Original Message-----
> From: Jianyong Wu <jianyong.wu@arm.com>
> Sent: Wednesday, November 11, 2020 2:22 PM
> To: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org;
> tglx@linutronix.de; pbonzini@redhat.com; sean.j.christopherson@intel.com;
> maz@kernel.org; richardcochran@gmail.com; Mark Rutland
> <Mark.Rutland@arm.com>; will@kernel.org; Suzuki Poulose
> <Suzuki.Poulose@arm.com>; Andre Przywara <Andre.Przywara@arm.com>;
> Steven Price <Steven.Price@arm.com>
> Cc: linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> kvmarm@lists.cs.columbia.edu; kvm@vger.kernel.org; Steve Capper
> <Steve.Capper@arm.com>; Justin He <Justin.He@arm.com>; Jianyong Wu
> <Jianyong.Wu@arm.com>; nd <nd@arm.com>
> Subject: [PATCH v15 0/9] Enable ptp_kvm for arm/arm64
>
> Currently, we offen use ntp (sync time with remote network clock) to sync
> time in VM. But the precision of ntp is subject to network delay so it's difficult
> to sync time in a high precision.
>
> kvm virtual ptp clock (ptp_kvm) offers another way to sync time in VM, as
> the remote clock locates in the host instead of remote network clock.
> It targets to sync time between guest and host in virtualization environment
> and in this way, we can keep the time of all the VMs running in the same host
> in sync. In general, the delay of communication between host and guest is
> quiet small, so ptp_kvm can offer time sync precision up to in order of
> nanosecond. Please keep in mind that ptp_kvm just limits itself to be a
> channel which transmit the remote clock from host to guest and leaves the
> time sync jobs to an application, eg. chrony, in usersapce in VM.
>
> How ptp_kvm works:
> After ptp_kvm initialized, there will be a new device node under /dev called
> ptp%d. A guest userspace service, like chrony, can use this device to get host
> walltime, sometimes also counter cycle, which depends on the service it calls.
> Then this guest userspace service can use those data to do the time sync for
> guest.
> here is a rough sketch to show how kvm ptp clock works.
>
> |----------------------------| |--------------------------|
> | guest userspace | | host |
> |ioctl -> /dev/ptp%d | | |
> | ^ | | | |
> |----------------------------| | |
> | | | guest kernel | | |
> | | V (get host walltime/counter cycle) |
> | ptp_kvm -> hypercall - - - - - - - - - - ->hypercall service |
> | <- - - - - - - - - - - - |
> |----------------------------| |--------------------------|
>
> 1. time sync service in guest userspace call ptp device through /dev/ptp%d.
> 2. ptp_kvm module in guest recive this request then invoke hypercall to
> route into host kernel to request host walltime/counter cycle.
> 3. ptp_kvm hypercall service in host response to the request and send data
> back.
> 4. ptp (not ptp_kvm) in guest copy the data to userspace.
>
> This ptp_kvm implementation focuses itself to step 2 and 3 and step 2 works
> in guest comparing step 3 works in host kernel.
>
> change log:
>
> from v14 to v15
> (1) enable ptp_kvm on arm32 guest, also ptp_kvm has been tested on
> both arm64 and arm32 guest running on arm64 kvm host.
> (2) move arch-agnostic part of ptp_kvm.rst into timekeeping.rst.
> (3) rename KVM_CAP_ARM_PTP_KVM to KVM_CAP_PTP_KVM as it
> should be arch agnostic.
> (4) add description for KVM_CAP_PTP_KVM in
> Documentation/virt/kvm/api.rst.
> (5) adjust dependency in Kconfig for ptp_kvm.
> (6) refine multi-arch process in driver/ptp/Makefile.
> (7) fix make pdfdocs htmldocs issue for ptp_kvm doc.
> (8) address other issues from comments in v14.
> (9) fold hypercall service of ptp_kvm as a function.
> (10) rebase to 5.10-rc3.
>
> from v13 to v14
> (1) rebase code on 5.9-rc3.
> (2) add a document to introduce implementation of PTP_KVM on arm64.
> (3) fix comments issue in hypercall.c.
> (4) export arm_smccc_1_1_get_conduit using EXPORT_SYMBOL_GPL.
> (5) fix make issue on x86 reported by kernel test robot.
>
> from v12 to v13:
> (1) rebase code on 5.8-rc1.
> (2) this patch set base on 2 patches of 1/8 and 2/8 from Will Decon.
> (3) remove the change to ptp device code of extend getcrosststamp.
> (4) remove the mechanism of letting user choose the counter type in
> ptp_kvm for arm64.
> (5) add virtual counter option in ptp_kvm service to let user choose the
> specific counter explicitly.
>
> from v11 to v12:
> (1) rebase code on 5.7-rc6 and rebase 2 patches from Will Decon
> including 1/11 and 2/11. as these patches introduce discover mechanism of
> vendor smccc service.
> (2) rebase ptp_kvm hypercall service from standard smccc to vendor
> smccc and add ptp_kvm to vendor smccc service discover mechanism.
> (3) add detail of why we need ptp_kvm and how ptp_kvm works in cover
> letter.
>
> from v10 to v11:
> (1) rebase code on 5.7-rc2.
> (2) remove support for arm32, as kvm support for arm32 will be removed
> [1]
> (3) add error report in ptp_kvm initialization.
>
> from v9 to v10:
> (1) change code base to v5.5.
> (2) enable ptp_kvm both for arm32 and arm64.
> (3) let user choose which of virtual counter or physical counter should
> return when using crosstimestamp mode of ptp_kvm for arm/arm64.
> (4) extend input argument for getcrosstimestamp API.
>
> from v8 to v9:
> (1) move ptp_kvm.h to driver/ptp/
> (2) replace license declaration of ptp_kvm.h the same with other header
> files in the same directory.
>
> from v7 to v8:
> (1) separate adding clocksource id for arm_arch_counter as a single patch.
> (2) update commit message for patch 4/8.
> (3) refine patch 7/8 and patch 8/8 to make them more independent.
>
> from v5 to v6:
> (1) apply Mark's patch[4] to get SMCCC conduit.
> (2) add mechanism to recognize current clocksource by add
> clocksouce_id value into struct clocksource instead of method in patch-v5.
> (3) rename kvm_arch_ptp_get_clock_fn into
> kvm_arch_ptp_get_crosststamp.
>
> from v4 to v5:
> (1) remove hvc delay compensasion as it should leave to userspace.
> (2) check current clocksource in hvc call service.
> (3) expose current clocksource by adding it to system_time_snapshot.
> (4) add helper to check if clocksource is arm_arch_counter.
> (5) rename kvm_ptp.c to ptp_kvm_common.c
>
> from v3 to v4:
> (1) fix clocksource of ptp_kvm to arch_sys_counter.
> (2) move kvm_arch_ptp_get_clock_fn into arm_arch_timer.c
> (3) subtract cntvoff before return cycles from host.
> (4) use ktime_get_snapshot instead of getnstimeofday and
> get_current_counterval to return time and counter value.
> (5) split ktime and counter into two 32-bit block respectively to avoid
> Y2038-safe issue.
> (6) set time compensation to device time as half of the delay of hvc call.
> (7) add ARM_ARCH_TIMER as dependency of ptp_kvm for arm64.
>
> from v2 to v3:
> (1) fix some issues in commit log.
> (2) add some receivers in send list.
>
> from v1 to v2:
> (1) move arch-specific code from arch/ to driver/ptp/
> (2) offer mechanism to inform userspace if ptp_kvm service is available.
> (3) separate ptp_kvm code for arm64 into hypervisor part and guest part.
> (4) add API to expose monotonic clock and counter value.
> (5) refine code: remove no necessary part and reconsitution.
>
> [1] https://patchwork.kernel.org/cover/11373351/
>
>
> Jianyong Wu (6):
> ptp: Reorganize ptp_kvm module to make it arch-independent.
> clocksource: Add clocksource id for arm arch counter
> arm64/kvm: Add hypercall service for kvm ptp.
> ptp: arm/arm64: Enable ptp_kvm for arm/arm64
> doc: add ptp_kvm introduction for arm64 support
> arm64: Add kvm capability check extension for ptp_kvm
>
> Thomas Gleixner (1):
> time: Add mechanism to recognize clocksource in time_get_snapshot
>
> Will Deacon (2):
> arm64: Probe for the presence of KVM hypervisor
> arm/arm64: KVM: Advertise KVM UID to guests via SMCCC
>
> Documentation/virt/kvm/api.rst | 9 ++
> Documentation/virt/kvm/arm/index.rst | 1 +
> Documentation/virt/kvm/arm/ptp_kvm.rst | 29 +++++++
> Documentation/virt/kvm/timekeeping.rst | 35 ++++++++
> arch/arm/kernel/setup.c | 1 +
> arch/arm64/kernel/setup.c | 1 +
> arch/arm64/kvm/arm.c | 1 +
> arch/arm64/kvm/hypercalls.c | 88 +++++++++++++++++--
> drivers/clocksource/arm_arch_timer.c | 30 +++++++
> drivers/firmware/smccc/smccc.c | 37 ++++++++
> drivers/ptp/Kconfig | 2 +-
> drivers/ptp/Makefile | 2 +
> drivers/ptp/ptp_kvm.h | 11 +++
> drivers/ptp/ptp_kvm_arm.c | 44 ++++++++++
> drivers/ptp/{ptp_kvm.c => ptp_kvm_common.c} | 85 +++++-------------
> drivers/ptp/ptp_kvm_x86.c | 95 +++++++++++++++++++++
> include/linux/arm-smccc.h | 60 +++++++++++++
> include/linux/clocksource.h | 6 ++
> include/linux/clocksource_ids.h | 12 +++
> include/linux/timekeeping.h | 12 +--
> include/uapi/linux/kvm.h | 1 +
> kernel/time/clocksource.c | 2 +
> kernel/time/timekeeping.c | 1 +
> 23 files changed, 488 insertions(+), 77 deletions(-) create mode 100644
> Documentation/virt/kvm/arm/ptp_kvm.rst
> create mode 100644 drivers/ptp/ptp_kvm.h create mode 100644
> drivers/ptp/ptp_kvm_arm.c rename drivers/ptp/{ptp_kvm.c =>
> ptp_kvm_common.c} (60%) create mode 100644
> drivers/ptp/ptp_kvm_x86.c create mode 100644
> include/linux/clocksource_ids.h
>
> --
> 2.17.1