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    SubjectRe: [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest
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    On 08/08/2019 16:29, Steven Price wrote:
    > On 04/08/2019 10:53, Marc Zyngier wrote:
    >> On Fri, 2 Aug 2019 15:50:17 +0100
    >> Steven Price <steven.price@arm.com> wrote:
    >>
    >>> Enable paravirtualization features when running under a hypervisor
    >>> supporting the PV_TIME_ST hypercall.
    >>>
    >>> For each (v)CPU, we ask the hypervisor for the location of a shared
    >>> page which the hypervisor will use to report stolen time to us. We set
    >>> pv_time_ops to the stolen time function which simply reads the stolen
    >>> value from the shared page for a VCPU. We guarantee single-copy
    >>> atomicity using READ_ONCE which means we can also read the stolen
    >>> time for another VCPU than the currently running one while it is
    >>> potentially being updated by the hypervisor.
    >>>
    >>> Signed-off-by: Steven Price <steven.price@arm.com>
    >>> ---
    >>> arch/arm64/kernel/Makefile | 1 +
    >>> arch/arm64/kernel/kvm.c | 155 +++++++++++++++++++++++++++++++++++++

    [...]

    >>> +static int __init kvm_guest_init(void)
    >>> +{
    >>> + int ret = 0;
    >>> +
    >>> + if (!has_kvm_steal_clock())
    >>> + return 0;
    >>> +
    >>> + ret = kvm_arm_init_stolen_time();
    >>> + if (ret)
    >>> + return ret;
    >>> +
    >>> + pv_ops.time.steal_clock = kvm_steal_clock;
    >>> +
    >>> + static_key_slow_inc(&paravirt_steal_enabled);
    >>> + if (steal_acc)
    >>> + static_key_slow_inc(&paravirt_steal_rq_enabled);
    >>> +
    >>> + pr_info("using stolen time PV\n");
    >>> +
    >>> + return 0;
    >>> +}
    >>> +early_initcall(kvm_guest_init);
    >>
    >> Is there any reason why we wouldn't directly call into this rather than
    >> using an initcall?
    >
    > I'm not sure where the direct call would go - any pointers?

    I'd be temped to say arch/arm64/kernel/time.c:time_init(), provided that
    there is no issue with the CPU hotplug lock (I remember hitting that a
    while ago).

    M.
    --
    Jazz is not dead, it just smells funny...

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