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Date: Thu, 14 Jan 2021 14:00:07 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v5 18/21] powerpc: move NMI entry/exit code into wrapper
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
 linuxppc-dev@lists.ozlabs.org
References: <20210113073215.516986-1-npiggin@gmail.com>
 <20210113073215.516986-19-npiggin@gmail.com>
 <b8006c6e-0828-66b7-067f-cbfd0ddf99a1@csgroup.eu>
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Excerpts from Christophe Leroy's message of January 14, 2021 1:13 am:
>=20
>=20
> Le 13/01/2021 =C3=A0 08:32, Nicholas Piggin a =C3=A9crit=C2=A0:
>> This moves the common NMI entry and exit code into the interrupt handler
>> wrappers.
>>=20
>> This changes the behaviour of soft-NMI (watchdog) and HMI interrupts, an=
d
>> also MCE interrupts on 64e, by adding missing parts of the NMI entry to
>> them.
>>=20
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>   arch/powerpc/include/asm/interrupt.h | 24 ++++++++++++++++
>>   arch/powerpc/kernel/mce.c            | 11 --------
>>   arch/powerpc/kernel/traps.c          | 42 +++++-----------------------
>>   arch/powerpc/kernel/watchdog.c       | 10 +++----
>>   4 files changed, 35 insertions(+), 52 deletions(-)
>>=20
>> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include=
/asm/interrupt.h
>> index e278dffe7657..01192e213f9a 100644
>> --- a/arch/powerpc/include/asm/interrupt.h
>> +++ b/arch/powerpc/include/asm/interrupt.h
>> @@ -95,14 +95,38 @@ static inline void interrupt_async_exit_prepare(stru=
ct pt_regs *regs, struct int
>>   }
>>  =20
>>   struct interrupt_nmi_state {
>> +#ifdef CONFIG_PPC64
>> +	u8 ftrace_enabled;
>> +#endif
>>   };
>>  =20
>>   static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, s=
truct interrupt_nmi_state *state)
>>   {
>> +#ifdef CONFIG_PPC64
>> +	state->ftrace_enabled =3D this_cpu_get_ftrace_enabled();
>> +	this_cpu_set_ftrace_enabled(0);
>> +#endif
>> +
>> +	/*
>> +	 * Do not use nmi_enter() for pseries hash guest taking a real-mode
>> +	 * NMI because not everything it touches is within the RMA limit.
>> +	 */
>> +	if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64) ||
>> +			!firmware_has_feature(FW_FEATURE_LPAR) ||
>> +			radix_enabled() || (mfmsr() & MSR_DR))
>> +		nmi_enter();
>>   }
>>  =20
>>   static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, st=
ruct interrupt_nmi_state *state)
>>   {
>> +	if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64) ||
>> +			!firmware_has_feature(FW_FEATURE_LPAR) ||
>> +			radix_enabled() || (mfmsr() & MSR_DR))
>> +		nmi_exit();
>> +
>> +#ifdef CONFIG_PPC64
>> +	this_cpu_set_ftrace_enabled(state->ftrace_enabled);
>> +#endif
>>   }
>>  =20
>>   /**
>> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
>> index 54269947113d..51456217ec40 100644
>> --- a/arch/powerpc/kernel/mce.c
>> +++ b/arch/powerpc/kernel/mce.c
>> @@ -592,12 +592,6 @@ EXPORT_SYMBOL_GPL(machine_check_print_event_info);
>>   DEFINE_INTERRUPT_HANDLER_NMI(machine_check_early)
>>   {
>>   	long handled =3D 0;
>> -	u8 ftrace_enabled =3D this_cpu_get_ftrace_enabled();
>> -
>> -	this_cpu_set_ftrace_enabled(0);
>> -	/* Do not use nmi_enter/exit for pseries hpte guest */
>> -	if (radix_enabled() || !firmware_has_feature(FW_FEATURE_LPAR))
>> -		nmi_enter();
>>  =20
>>   	hv_nmi_check_nonrecoverable(regs);
>>  =20
>> @@ -607,11 +601,6 @@ DEFINE_INTERRUPT_HANDLER_NMI(machine_check_early)
>>   	if (ppc_md.machine_check_early)
>>   		handled =3D ppc_md.machine_check_early(regs);
>>  =20
>> -	if (radix_enabled() || !firmware_has_feature(FW_FEATURE_LPAR))
>> -		nmi_exit();
>> -
>> -	this_cpu_set_ftrace_enabled(ftrace_enabled);
>> -
>>   	return handled;
>>   }
>>  =20
>> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
>> index b4f23e871a68..43d23232ef5c 100644
>> --- a/arch/powerpc/kernel/traps.c
>> +++ b/arch/powerpc/kernel/traps.c
>> @@ -435,11 +435,6 @@ DEFINE_INTERRUPT_HANDLER_NMI(system_reset_exception=
)
>>   {
>>   	unsigned long hsrr0, hsrr1;
>>   	bool saved_hsrrs =3D false;
>> -	u8 ftrace_enabled =3D this_cpu_get_ftrace_enabled();
>> -
>> -	this_cpu_set_ftrace_enabled(0);
>> -
>> -	nmi_enter();
>>  =20
>>   	/*
>>   	 * System reset can interrupt code where HSRRs are live and MSR[RI]=
=3D1.
>> @@ -511,10 +506,6 @@ DEFINE_INTERRUPT_HANDLER_NMI(system_reset_exception=
)
>>   		mtspr(SPRN_HSRR1, hsrr1);
>>   	}
>>  =20
>> -	nmi_exit();
>> -
>> -	this_cpu_set_ftrace_enabled(ftrace_enabled);
>> -
>>   	/* What should we do here? We could issue a shutdown or hard reset. *=
/
>>  =20
>>   	return 0;
>> @@ -792,6 +783,12 @@ int machine_check_generic(struct pt_regs *regs)
>>   #endif /* everything else */
>>  =20
>>  =20
>> +/*
>> + * BOOK3S_64 does not call this handler as a non-maskable interrupt
>> + * (it uses its own early real-mode handler to handle the MCE proper
>> + * and then raises irq_work to call this handler when interrupts are
>> + * enabled).
>> + */
>>   #ifdef CONFIG_PPC_BOOK3S_64
>>   DEFINE_INTERRUPT_HANDLER_ASYNC(machine_check_exception)
>>   #else
>> @@ -800,20 +797,6 @@ DEFINE_INTERRUPT_HANDLER_NMI(machine_check_exceptio=
n)
>>   {
>>   	int recover =3D 0;
>>  =20
>> -	/*
>> -	 * BOOK3S_64 does not call this handler as a non-maskable interrupt
>> -	 * (it uses its own early real-mode handler to handle the MCE proper
>> -	 * and then raises irq_work to call this handler when interrupts are
>> -	 * enabled).
>> -	 *
>> -	 * This is silly. The BOOK3S_64 should just call a different function
>> -	 * rather than expecting semantics to magically change. Something
>> -	 * like 'non_nmi_machine_check_exception()', perhaps?
>> -	 */
>> -	const bool nmi =3D !IS_ENABLED(CONFIG_PPC_BOOK3S_64);
>> -
>> -	if (nmi) nmi_enter();
>> -
>>   	__this_cpu_inc(irq_stat.mce_exceptions);
>>  =20
>>   	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
>> @@ -838,24 +821,17 @@ DEFINE_INTERRUPT_HANDLER_NMI(machine_check_excepti=
on)
>>   	if (check_io_access(regs))
>>   		goto bail;
>>  =20
>> -	if (nmi) nmi_exit();
>> -
>=20
> IIRC, not doing the nmi_exit() before the die() is problematic.
>=20
> See=20
> https://github.com/linuxppc/linux/commit/daf00ae71dad8aa05965713c62558aee=
bf2df48e#diff-70077148c383252ca949063eaf1b0250620e4607b43f4ef3fd2d8f448a83a=
b0a

Yes good catch. Maybe putting it into a nmi_die() or having die=20
explicitly check for the NMI case might be the go.

Thanks,
Nick