• Michael Kelley's avatar
    x86/hyperv: Initialize clockevents earlier in CPU onlining · 4df4cb9e
    Michael Kelley authored
    Hyper-V has historically initialized stimer-based clockevents late in the
    process of onlining a CPU because clockevents depend on stimer
    interrupts. In the original Hyper-V design, stimer interrupts generate a
    VMbus message, so the VMbus machinery must be running first, and VMbus
    can't be initialized until relatively late. On x86/64, LAPIC timer based
    clockevents are used during early initialization before VMbus and
    stimer-based clockevents are ready, and again during CPU offlining after
    the stimer clockevents have been shut down.
    
    Unfortunately, this design creates problems when offlining CPUs for
    hibernation or other purposes. stimer-based clockevents are shut down
    relatively early in the offlining process, so clockevents_unbind_device()
    must be used to fallback to the LAPIC-based clockevents for the remainder
    of the offlining process.  Furthermore, the late initialization and early
    shutdown of stimer-based clockevents doesn't work well on ARM64 since there
    is no other timer like the LAPIC to fallback to. So CPU onlining and
    offlining doesn't work properly.
    
    Fix this by recognizing that stimer Direct Mode is the normal path for
    newer versions of Hyper-V on x86/64, and the only path on other
    architectures. With stimer Direct Mode, stimer interrupts don't require any
    VMbus machinery. stimer clockevents can be initialized and shut down
    consistent with how it is done for other clockevent devices. While the old
    VMbus-based stimer interrupts must still be supported for backward
    compatibility on x86, that mode of operation can be treated as legacy.
    
    So add a new Hyper-V stimer entry in the CPU hotplug state list, and use
    that new state when in Direct Mode. Update the Hyper-V clocksource driver
    to allocate and initialize stimer clockevents earlier during boot. Update
    Hyper-V initialization and the VMbus driver to use this new design. As a
    result, the LAPIC timer is no longer used during boot or CPU
    onlining/offlining and clockevents_unbind_device() is not called.  But
    retain the old design as a legacy implementation for older versions of
    Hyper-V that don't support Direct Mode.
    Signed-off-by: default avatarMichael Kelley <mikelley@microsoft.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Tested-by: default avatarDexuan Cui <decui@microsoft.com>
    Reviewed-by: default avatarDexuan Cui <decui@microsoft.com>
    Link: https://lkml.kernel.org/r/1573607467-9456-1-git-send-email-mikelley@microsoft.com
    4df4cb9e
hyperv_timer.h 2.91 KB