Re: [PATCH v2] powerpc: Handle MCE on POWER9 with only DSISR bit 33 set

[Nicholas Piggin <nicholas.piggin@gmail.com>]

On Thu, 21 Sep 2017 12:04:34 +1000
Michael Neuling <mikey@neuling.org> wrote:

> On POWER9 DD2.1 and below, it's possible to get Machine Check
> Exception (MCE) where only DSISR bit 33 is set. This will result in
> the linux MCE handler seeing an unknown event, which triggers linux to
> crash.
> 
> We change this by detecting unknown events in the MCE handler and
> marking them as handled so that we no longer crash. We do this only on
> chip revisions known to have this problem.
> 
> MCE that occurs like this is spurious, so we don't need to do anything
> in terms of servicing it. If there is something that needs to be
> serviced, the CPU will raise the MCE again with the correct DSISR so
> that it can be serviced properly.
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> ---
> v2 update commit message based on Balbir's comments
> ---
>  arch/powerpc/kernel/mce_power.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
> index b76ca198e0..72ec667136 100644
> --- a/arch/powerpc/kernel/mce_power.c
> +++ b/arch/powerpc/kernel/mce_power.c
> @@ -595,6 +595,7 @@ static long mce_handle_error(struct pt_regs *regs,
>  	uint64_t addr;
>  	uint64_t srr1 = regs->msr;
>  	long handled;
> +	unsigned long pvr;
>  
>  	if (SRR1_MC_LOADSTORE(srr1))
>  		handled = mce_handle_derror(regs, dtable, &mce_err, &addr);
> @@ -604,6 +605,20 @@ static long mce_handle_error(struct pt_regs *regs,
>  	if (!handled && mce_err.error_type == MCE_ERROR_TYPE_UE)
>  		handled = mce_handle_ue_error(regs);
>  
> +	/*
> +	 * On POWER9 DD2.1 and below, it's possible to get machine
> +	 * check where only DSISR bit 33 is set. This will result in
> +	 * the MCE handler seeing an unknown event and us crashing.
> +	 * Change this to mark as handled on these revisions.
> +	 */
> +	pvr = mfspr(SPRN_PVR);
> +	if (((PVR_VER(pvr) == PVR_POWER9) &&
> +	     (PVR_CFG(pvr) == 2) &&
> +	     (PVR_MIN(pvr) <= 1)) || cpu_has_feature(CPU_FTR_POWER9_DD1))
> +		/* DD2.1 and below */
> +		if (mce_err.error_type == MCE_ERROR_TYPE_UNKNOWN)
> +		    handled = 1;

I might be missing something, but can you just do

  if (regs->dsisr == 0x40000000)
      return 1;

In __machine_check_early_realmode_p9() ?

Thanks,
Nick