On Wed, 2018-01-17 at 09:51:13 UTC, Paul Mackerras wrote: > 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: Paul Mackerras <paulus@xxxxxxxxxx> Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/d075745d893c78730e4a3b7a60fca2 cheers
