• Don Zickus's avatar
    x86, nmi: Create new NMI handler routines · c9126b2e
    Don Zickus authored
    The NMI handlers used to rely on the notifier infrastructure.  This worked
    great until we wanted to support handling multiple events better.
    
    One of the key ideas to the nmi handling is to process _all_ the handlers for
    each NMI.  The reason behind this switch is because NMIs are edge triggered.
    If enough NMIs are triggered, then they could be lost because the cpu can
    only latch at most one NMI (besides the one currently being processed).
    
    In order to deal with this we have decided to process all the NMI handlers
    for each NMI.  This allows the handlers to determine if they recieved an
    event or not (the ones that can not determine this will be left to fend
    for themselves on the unknown NMI list).
    
    As a result of this change it is now possible to have an extra NMI that
    was destined to be received for an already processed event.  Because the
    event was processed in the previous NMI, this NMI gets dropped and becomes
    an 'unknown' NMI.  This of course will cause printks that scare people.
    
    However, we prefer to have extra NMIs as opposed to losing NMIs and as such
    are have developed a basic mechanism to catch most of them.  That will be
    a later patch.
    
    To accomplish this idea, I unhooked the nmi handlers from the notifier
    routines and created a new mechanism loosely based on doIRQ.  The reason
    for this is the notifier routines have a couple of shortcomings.  One we
    could't guarantee all future NMI handlers used NOTIFY_OK instead of
    NOTIFY_STOP.  Second, we couldn't keep track of the number of events being
    handled in each routine (most only handle one, perf can handle more than one).
    Third, I wanted to eventually display which nmi handlers are registered in
    the system in /proc/interrupts to help see who is generating NMIs.
    
    The patch below just implements the new infrastructure but doesn't wire it up
    yet (that is the next patch).  Its design is based on doIRQ structs and the
    atomic notifier routines.  So the rcu stuff in the patch isn't entirely untested
    (as the notifier routines have soaked it) but it should be double checked in
    case I copied the code wrong.
    Signed-off-by: default avatarDon Zickus <dzickus@redhat.com>
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1317409584-23662-3-git-send-email-dzickus@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
    c9126b2e
nmi.h 1.77 KB