Re: [4/6] KVM: PPC: Book3S HV: Improve handling of debug-trigger HMIs on POWER9

[Michael Ellerman <patch-notifications@ellerman.id.au>]

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@ozlabs.org>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/d075745d893c78730e4a3b7a60fca2

cheers