• Marc Zyngier's avatar
    KVM: arm/arm64: Handle forward time correction gracefully · 1c5631c7
    Marc Zyngier authored
    On a host that runs NTP, corrections can have a direct impact on
    the background timer that we program on the behalf of a vcpu.
    
    In particular, NTP performing a forward correction will result in
    a timer expiring sooner than expected from a guest point of view.
    Not a big deal, we kick the vcpu anyway.
    
    But on wake-up, the vcpu thread is going to perform a check to
    find out whether or not it should block. And at that point, the
    timer check is going to say "timer has not expired yet, go back
    to sleep". This results in the timer event being lost forever.
    
    There are multiple ways to handle this. One would be record that
    the timer has expired and let kvm_cpu_has_pending_timer return
    true in that case, but that would be fairly invasive. Another is
    to check for the "short sleep" condition in the hrtimer callback,
    and restart the timer for the remaining time when the condition
    is detected.
    
    This patch implements the latter, with a bit of refactoring in
    order to avoid too much code duplication.
    
    Cc: <stable@vger.kernel.org>
    Reported-by: default avatarAlexander Graf <agraf@suse.de>
    Reviewed-by: default avatarAlexander Graf <agraf@suse.de>
    Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
    1c5631c7
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