• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Improve handling of debug-trigger HMIs on POWER9 · d075745d
    Paul Mackerras authored
    Hypervisor maintenance interrupts (HMIs) are generated by various
    causes, signalled by bits in the hypervisor maintenance exception
    register (HMER).  In most cases calling OPAL to handle the interrupt
    is the correct thing to do, but the "debug trigger" HMIs signalled by
    PPC bit 17 (bit 46) of HMER are used to invoke software workarounds
    for hardware bugs, and OPAL does not have any code to handle this
    cause.  The debug trigger HMI is used in POWER9 DD2.0 and DD2.1 chips
    to work around a hardware bug in executing vector load instructions to
    cache inhibited memory.  In POWER9 DD2.2 chips, it is generated when
    conditions are detected relating to threads being in TM (transactional
    memory) suspended mode when the core SMT configuration needs to be
    reconfigured.
    
    The kernel currently has code to detect the vector CI load condition,
    but only when the HMI occurs in the host, not when it occurs in a
    guest.  If a HMI occurs in the guest, it is always passed to OPAL, and
    then we always re-sync the timebase, because the HMI cause might have
    been a timebase error, for which OPAL would re-sync the timebase, thus
    removing the timebase offset which KVM applied for the guest.  Since
    we don't know what OPAL did, we don't know whether to subtract the
    timebase offset from the timebase, so instead we re-sync the timebase.
    
    This adds code to determine explicitly what the cause of a debug
    trigger HMI will be.  This is based on a new device-tree property
    under the CPU nodes called ibm,hmi-special-triggers, if it is
    present, or otherwise based on the PVR (processor version register).
    The handling of debug trigger HMIs is pulled out into a separate
    function which can be called from the KVM guest exit code.  If this
    function handles and clears the HMI, and no other HMI causes remain,
    then we skip calling OPAL and we proceed to subtract the guest
    timebase offset from the timebase.
    
    The overall handling for HMIs that occur in the host (i.e. not in a
    KVM guest) is largely unchanged, except that we now don't set the flag
    for the vector CI load workaround on DD2.2 processors.
    
    This also removes a BUG_ON in the KVM code.  BUG_ON is generally not
    useful in KVM guest entry/exit code since it is difficult to handle
    the resulting trap gracefully.
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    d075745d
hmi.h 1.49 KB