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

[Nicholas Piggin]

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!

> 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

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;
 }