Excerpts from Ganesh Goudar's message of November 8, 2021 6:38 pm:
> In realmode mce handler we use irq_work_queue() to defer
> the processing of mce events, irq_work_queue() can only
> be called when translation is enabled because it touches
> memory outside RMA, hence we enable translation before
> calling irq_work_queue and disable on return, though it
> is not safe to do in realmode.
>
> To avoid this, program the decrementer and call the event
> processing functions from timer handler.
>
> Signed-off-by: Ganesh Goudar <ganes...@linux.ibm.com>
> ---
> arch/powerpc/include/asm/machdep.h | 2 +
> arch/powerpc/include/asm/mce.h | 2 +
> arch/powerpc/include/asm/paca.h | 1 +
> arch/powerpc/kernel/mce.c | 51 +++++++++++-------------
> arch/powerpc/kernel/time.c | 3 ++
> arch/powerpc/platforms/pseries/pseries.h | 1 +
> arch/powerpc/platforms/pseries/ras.c | 31 +-------------
> arch/powerpc/platforms/pseries/setup.c | 1 +
> 8 files changed, 34 insertions(+), 58 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/machdep.h
> b/arch/powerpc/include/asm/machdep.h
> index 764f2732a821..c89cc03c0f97 100644
> --- a/arch/powerpc/include/asm/machdep.h
> +++ b/arch/powerpc/include/asm/machdep.h
> @@ -103,6 +103,8 @@ struct machdep_calls {
> /* Called during machine check exception to retrive fixup address. */
> bool (*mce_check_early_recovery)(struct pt_regs *regs);
>
> + void (*machine_check_log_err)(void);
> +
> /* Motherboard/chipset features. This is a kind of general purpose
> * hook used to control some machine specific features (like reset
> * lines, chip power control, etc...).
> diff --git a/arch/powerpc/include/asm/mce.h b/arch/powerpc/include/asm/mce.h
> index 331d944280b8..187810f13669 100644
> --- a/arch/powerpc/include/asm/mce.h
> +++ b/arch/powerpc/include/asm/mce.h
> @@ -235,8 +235,10 @@ extern void machine_check_print_event_info(struct
> machine_check_event *evt,
> unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr);
> extern void mce_common_process_ue(struct pt_regs *regs,
> struct mce_error_info *mce_err);
> +extern void machine_check_raise_dec_intr(void);
No new externs on function declarations, they tell me.
> int mce_register_notifier(struct notifier_block *nb);
> int mce_unregister_notifier(struct notifier_block *nb);
> +void mce_run_late_handlers(void);
> #ifdef CONFIG_PPC_BOOK3S_64
> void flush_and_reload_slb(void);
> void flush_erat(void);
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index dc05a862e72a..f49180f8c9be 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -280,6 +280,7 @@ struct paca_struct {
> #endif
> #ifdef CONFIG_PPC_BOOK3S_64
> struct mce_info *mce_info;
> + atomic_t mces_to_process;
> #endif /* CONFIG_PPC_BOOK3S_64 */
> } ____cacheline_aligned;
>
> diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
> index fd829f7f25a4..45baa062ebc0 100644
> --- a/arch/powerpc/kernel/mce.c
> +++ b/arch/powerpc/kernel/mce.c
> @@ -28,19 +28,9 @@
>
> #include "setup.h"
>
> -static void machine_check_process_queued_event(struct irq_work *work);
> -static void machine_check_ue_irq_work(struct irq_work *work);
> static void machine_check_ue_event(struct machine_check_event *evt);
> static void machine_process_ue_event(struct work_struct *work);
>
> -static struct irq_work mce_event_process_work = {
> - .func = machine_check_process_queued_event,
> -};
> -
> -static struct irq_work mce_ue_event_irq_work = {
> - .func = machine_check_ue_irq_work,
> -};
> -
> static DECLARE_WORK(mce_ue_event_work, machine_process_ue_event);
>
> static BLOCKING_NOTIFIER_HEAD(mce_notifier_list);
> @@ -89,6 +79,12 @@ static void mce_set_error_info(struct machine_check_event
> *mce,
> }
> }
>
> +/* Raise decrementer interrupt */
> +void machine_check_raise_dec_intr(void)
> +{
> + set_dec(1);
> +}
The problem here is a timer can be scheduled (e.g., by an external
interrupt if it gets taken before the decrementer, then uses a
timer) and that set decr > 1. See logic in decrementer_set_next_event.
I _think_ the way to get around this would be to have the machine check
just use arch_irq_work_raise.
Then you could also only call the mce handler inside the
test_irq_work_pending() check and avoid the added function call on every
timer. That test should also be marked unlikely come to think of it, but
that's a side patchlet.
> +
> /*
> * Decode and save high level MCE information into per cpu buffer which
> * is an array of machine_check_event structure.
> @@ -135,6 +131,8 @@ void save_mce_event(struct pt_regs *regs, long handled,
> if (mce->error_type == MCE_ERROR_TYPE_UE)
> mce->u.ue_error.ignore_event = mce_err->ignore_event;
>
> + atomic_inc(&local_paca->mces_to_process);
> +
> if (!addr)
> return;
>
> @@ -217,7 +215,7 @@ void release_mce_event(void)
> get_mce_event(NULL, true);
> }
>
> -static void machine_check_ue_irq_work(struct irq_work *work)
> +static void machine_check_ue_work(void)
> {
> schedule_work(&mce_ue_event_work);
> }
> @@ -239,7 +237,7 @@ static void machine_check_ue_event(struct
> machine_check_event *evt)
> evt, sizeof(*evt));
>
> /* Queue work to process this event later. */
> - irq_work_queue(&mce_ue_event_irq_work);
> + machine_check_raise_dec_intr();
> }
>
> /*
> @@ -249,7 +247,6 @@ void machine_check_queue_event(void)
> {
> int index;
> struct machine_check_event evt;
> - unsigned long msr;
>
> if (!get_mce_event(&evt, MCE_EVENT_RELEASE))
> return;
> @@ -263,20 +260,7 @@ void machine_check_queue_event(void)
> memcpy(&local_paca->mce_info->mce_event_queue[index],
> &evt, sizeof(evt));
>
> - /*
> - * Queue irq work to process this event later. Before
> - * queuing the work enable translation for non radix LPAR,
> - * as irq_work_queue may try to access memory outside RMO
> - * region.
> - */
> - if (!radix_enabled() && firmware_has_feature(FW_FEATURE_LPAR)) {
> - msr = mfmsr();
> - mtmsr(msr | MSR_IR | MSR_DR);
> - irq_work_queue(&mce_event_process_work);
> - mtmsr(msr);
> - } else {
> - irq_work_queue(&mce_event_process_work);
> - }
Getting rid of these things would be very nice.
> + machine_check_raise_dec_intr();
> }
>
> void mce_common_process_ue(struct pt_regs *regs,
> @@ -338,7 +322,7 @@ static void machine_process_ue_event(struct work_struct
> *work)
> * process pending MCE event from the mce event queue. This function will be
> * called during syscall exit.
> */
> -static void machine_check_process_queued_event(struct irq_work *work)
> +static void machine_check_process_queued_event(void)
> {
> int index;
> struct machine_check_event *evt;
> @@ -363,6 +347,17 @@ static void machine_check_process_queued_event(struct
> irq_work *work)
> }
> }
>
> +void mce_run_late_handlers(void)
> +{
> + if (unlikely(atomic_read(&local_paca->mces_to_process))) {
> + if (ppc_md.machine_check_log_err)
> + ppc_md.machine_check_log_err();
> + machine_check_process_queued_event();
> + machine_check_ue_work();
> + atomic_dec(&local_paca->mces_to_process);
> + }
> +}
> +
> void machine_check_print_event_info(struct machine_check_event *evt,
> bool user_mode, bool in_guest)
> {
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index 934d8ae66cc6..2dc09d75d77c 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -597,6 +597,9 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
> irq_work_run();
> }
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + mce_run_late_handlers();
> +#endif
It looks like if (IS_ENABLED(CONFIG_PPC_BOOK3S_64)) should work here?
> now = get_tb();
> if (now >= *next_tb) {
> *next_tb = ~(u64)0;
> diff --git a/arch/powerpc/platforms/pseries/pseries.h
> b/arch/powerpc/platforms/pseries/pseries.h
> index 3544778e06d0..0dc4f1027b30 100644
> --- a/arch/powerpc/platforms/pseries/pseries.h
> +++ b/arch/powerpc/platforms/pseries/pseries.h
> @@ -21,6 +21,7 @@ struct pt_regs;
> extern int pSeries_system_reset_exception(struct pt_regs *regs);
> extern int pSeries_machine_check_exception(struct pt_regs *regs);
> extern long pseries_machine_check_realmode(struct pt_regs *regs);
> +extern void pSeries_machine_check_log_err(void);
extern can be removed.
Thanks,
Nick
>
> #ifdef CONFIG_SMP
> extern void smp_init_pseries(void);
> diff --git a/arch/powerpc/platforms/pseries/ras.c
> b/arch/powerpc/platforms/pseries/ras.c
> index 56092dccfdb8..8613f9cc5798 100644
> --- a/arch/powerpc/platforms/pseries/ras.c
> +++ b/arch/powerpc/platforms/pseries/ras.c
> @@ -23,11 +23,6 @@ static DEFINE_SPINLOCK(ras_log_buf_lock);
>
> static int ras_check_exception_token;
>
> -static void mce_process_errlog_event(struct irq_work *work);
> -static struct irq_work mce_errlog_process_work = {
> - .func = mce_process_errlog_event,
> -};
> -
> #define EPOW_SENSOR_TOKEN 9
> #define EPOW_SENSOR_INDEX 0
>
> @@ -729,40 +724,16 @@ static int mce_handle_error(struct pt_regs *regs,
> struct rtas_error_log *errp)
> error_type = mce_log->error_type;
>
> disposition = mce_handle_err_realmode(disposition, error_type);
> -
> - /*
> - * Enable translation as we will be accessing per-cpu variables
> - * in save_mce_event() which may fall outside RMO region, also
> - * leave it enabled because subsequently we will be queuing work
> - * to workqueues where again per-cpu variables accessed, besides
> - * fwnmi_release_errinfo() crashes when called in realmode on
> - * pseries.
> - * Note: All the realmode handling like flushing SLB entries for
> - * SLB multihit is done by now.
> - */
> out:
> - msr = mfmsr();
> - mtmsr(msr | MSR_IR | MSR_DR);
> -
> disposition = mce_handle_err_virtmode(regs, errp, mce_log,
> disposition);
> -
> - /*
> - * Queue irq work to log this rtas event later.
> - * irq_work_queue uses per-cpu variables, so do this in virt
> - * mode as well.
> - */
> - irq_work_queue(&mce_errlog_process_work);
> -
> - mtmsr(msr);
> -
> return disposition;
> }
>
> /*
> * Process MCE rtas errlog event.
> */
> -static void mce_process_errlog_event(struct irq_work *work)
> +void pSeries_machine_check_log_err(void)
> {
> struct rtas_error_log *err;
>
> diff --git a/arch/powerpc/platforms/pseries/setup.c
> b/arch/powerpc/platforms/pseries/setup.c
> index f79126f16258..54bd7bdb7e92 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -1085,6 +1085,7 @@ define_machine(pseries) {
> .system_reset_exception = pSeries_system_reset_exception,
> .machine_check_early = pseries_machine_check_realmode,
> .machine_check_exception = pSeries_machine_check_exception,
> + .machine_check_log_err = pSeries_machine_check_log_err,
> #ifdef CONFIG_KEXEC_CORE
> .machine_kexec = pSeries_machine_kexec,
> .kexec_cpu_down = pseries_kexec_cpu_down,
> --
> 2.26.2
>
>
