[PATCH v7 39/42] powerpc: move NMI entry/exit code into wrapper

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:
> Excerpts from Michael Ellerman's message of February 4, 2021 8:15 pm:
>> Nicholas Piggin <npiggin at gmail.com> writes:
>>> This moves the common NMI entry and exit code into the interrupt handler
>>> wrappers.
>>>
>>> This changes the behaviour of soft-NMI (watchdog) and HMI interrupts, and
>>> also MCE interrupts on 64e, by adding missing parts of the NMI entry to
>>> them.
>>>
>>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>>> ---
>>>  arch/powerpc/include/asm/interrupt.h | 28 ++++++++++++++++++++++
>>>  arch/powerpc/kernel/mce.c            | 11 ---------
>>>  arch/powerpc/kernel/traps.c          | 35 +++++-----------------------
>>>  arch/powerpc/kernel/watchdog.c       | 10 ++++----
>>>  4 files changed, 38 insertions(+), 46 deletions(-)
>> 
>> This is unhappy when injecting SLB multi-hits:
>> 
>>   root at p86-2:~# echo PPC_SLB_MULTIHIT > /sys/kernel/debug/provoke-crash/DIRECT
>>   [  312.496026][ T1344] kernel BUG at arch/powerpc/include/asm/interrupt.h:152!
>>   [  312.496037][ T1344] Oops: Exception in kernel mode, sig: 5 [#1]
>>   [  312.496045][ T1344] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>
> pseries hash. Blast!

The worst kind.

>> 147 static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct interrupt_nmi_state *state)
>> 148 {
>> 149 	if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64) ||
>> 150 			!firmware_has_feature(FW_FEATURE_LPAR) ||
>> 151 			radix_enabled() || (mfmsr() & MSR_DR))
>> 152 		nmi_exit();
>> 
>> 
>> So presumably it's:
>> 
>> #define __nmi_exit()						\
>> 	do {							\
>> 		BUG_ON(!in_nmi());				\
>
> Yes that would be it, pseries machine check enables MMU half way through 
> so only one side of this triggers.
>
> The MSR_DR check is supposed to catch the other NMIs that run with MMU 
> on (perf, watchdog, etc). Suppose it could test TRAP(regs) explicitly
> although I wonder if we should also do this to keep things balanced

Yeah I think I like that. I'll give it a test.

cheers


> diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
> index 149cec2212e6..f57ca0c570be 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -719,6 +719,7 @@ static int mce_handle_err_virtmode(struct pt_regs *regs,
>  
>  static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
>  {
> +       unsigned long msr;
>         struct pseries_errorlog *pseries_log;
>         struct pseries_mc_errorlog *mce_log = NULL;
>         int disposition = rtas_error_disposition(errp);
> @@ -747,9 +748,12 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
>          *       SLB multihit is done by now.
>          */
>  out:
> -       mtmsr(mfmsr() | MSR_IR | MSR_DR);
> +       msr = mfmsr();
> +       mtmsr(msr | MSR_IR | MSR_DR);
>         disposition = mce_handle_err_virtmode(regs, errp, mce_log,
>                                               disposition);
> +       mtmsr(msr);
> +
>         return disposition;
>  }
>