On 03/12/2018 13:25, Andrew Jones wrote: > On Wed, Nov 28, 2018 at 02:45:15PM +0000, Steven Price wrote: >> This series add support for paravirtualized time for Arm64 guests and >> KVM hosts following the specification in Arm's document DEN 0057A: >> >> https://developer.arm.com/docs/den0057/a > > Hi Steven, > > As that specification is still a draft, then I guess this series is an > RFC. I just wanted to point that out, as I believe that tag should be > used in future postings until the spec is approved. Hi, Yes, sorry I should have included the RFC tag as we want feedback before the specification is finalised. > Regarding the spec, my understanding from kvm forum was that there was > still a need to explain why kvmclock, or an extension to kvmclock, is > insufficient. > > If there hasn't been anything written up about that yet, would you mind > doing so? There are obviously similarities to kvmclock, but there are a few differences that enable some optimisations: * The coefficient for scaling from native frequency to PV frequency is a 64 bit integer that can be efficiently multiplied on arm64 hardware. kvmclock provides us with a 32 bit multiplier. * Rather than providing an offset in the structure (via tsc_timestamp/system_time) the CPU's CNTVOFF support is used to provide a virtual counter than simply needs scaling (no offset is applied by the guest). Given this is seemed sensible not to confuse matters by (ab)using the existing kvmclock implementation. >> >> It implements support for Live Physical Time (LPT) which provides the >> guest with a method to derive a stable counter of time during which the >> guest is executing even when the guest is being migrated between hosts >> with different physical counter frequencies. > > Intel has TSC scaling. Is there any reason Arm is proposing a PV > solution instead of adding a similar virt extension? As Marc has already pointed out - hardware changes will take a while to happen, this works for today's systems. Thanks, Steve > > Thanks, > drew > >> >> It also implements support for stolen time, allowing the guest to >> identify time when it is forcibly not executing. >> >> Patch 1 provides some documentation >> Patches 2-4, 8 and 11 provide some refactoring of existing code >> Patch 5 implements the new PV_FEATURES discovery mechanism >> Patches 6-7 implement live physical time >> Patches 9-10 implement stolen time >> Patch 12 adds the 'PV_TIME' device for user space to enable the features >> >> Christoffer Dall (2): >> KVM: arm/arm64: Factor out hypercall handling from PSCI code >> KVM: Export mark_page_dirty_in_slot >> >> Steven Price (10): >> KVM: arm64: Document PV-time interface >> arm/arm64: Provide a wrapper for SMCCC 1.1 calls >> arm/arm64: Make use of the SMCCC 1.1 wrapper >> KVM: arm64: Implement PV_FEATURES call >> KVM: arm64: Support Live Physical Time reporting >> clocksource: arm_arch_timer: Use paravirtualized LPT >> KVM: arm64: Support stolen time reporting via shared page >> arm64: Retrieve stolen time as paravirtualized guest >> KVM: Allow kvm_device_ops to be const >> KVM: arm64: Provide a PV_TIME device to user space >> >> Documentation/virtual/kvm/arm/pvtime.txt | 169 ++++++++++++++ >> arch/arm/kvm/Makefile | 2 +- >> arch/arm/kvm/handle_exit.c | 2 +- >> arch/arm/mm/proc-v7-bugs.c | 46 ++-- >> arch/arm64/include/asm/arch_timer.h | 32 ++- >> arch/arm64/include/asm/kvm_host.h | 16 ++ >> arch/arm64/include/asm/kvm_mmu.h | 2 + >> arch/arm64/include/asm/pvclock-abi.h | 32 +++ >> arch/arm64/include/uapi/asm/kvm.h | 8 + >> arch/arm64/kernel/Makefile | 1 + >> arch/arm64/kernel/cpu_errata.c | 47 +--- >> arch/arm64/kernel/cpuinfo.c | 2 +- >> arch/arm64/kernel/kvm.c | 156 +++++++++++++ >> arch/arm64/kvm/Kconfig | 1 + >> arch/arm64/kvm/Makefile | 2 + >> arch/arm64/kvm/handle_exit.c | 4 +- >> drivers/clocksource/arm_arch_timer.c | 176 ++++++++++++++- >> include/kvm/arm_arch_timer.h | 2 + >> include/kvm/arm_hypercalls.h | 44 ++++ >> include/kvm/arm_psci.h | 2 +- >> include/kvm/arm_pv.h | 28 +++ >> include/linux/arm-smccc.h | 45 ++++ >> include/linux/cpuhotplug.h | 1 + >> include/linux/kvm_host.h | 5 +- >> include/linux/kvm_types.h | 2 + >> include/uapi/linux/kvm.h | 2 + >> virt/kvm/arm/arm.c | 25 +- >> virt/kvm/arm/hypercalls.c | 276 +++++++++++++++++++++++ >> virt/kvm/arm/mmu.c | 44 ++++ >> virt/kvm/arm/psci.c | 76 +------ >> virt/kvm/arm/pvtime.c | 243 ++++++++++++++++++++ >> virt/kvm/kvm_main.c | 12 +- >> 32 files changed, 1348 insertions(+), 157 deletions(-) >> create mode 100644 Documentation/virtual/kvm/arm/pvtime.txt >> create mode 100644 arch/arm64/include/asm/pvclock-abi.h >> create mode 100644 arch/arm64/kernel/kvm.c >> create mode 100644 include/kvm/arm_hypercalls.h >> create mode 100644 include/kvm/arm_pv.h >> create mode 100644 virt/kvm/arm/hypercalls.c >> create mode 100644 virt/kvm/arm/pvtime.c >> >> -- >> 2.19.2 >> >> _______________________________________________ >> kvmarm mailing list >> kvmarm@xxxxxxxxxxxxxxxxxxxxx >> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
