From ec233ede4c8654894610ea54f4dae7adc954ac62 Mon Sep 17 00:00:00 2001 From: Sukadev Bhattiprolu Date: Tue, 7 Nov 2017 18:23:53 -0800 Subject: [PATCH] powerpc: Add support for setting SPRN_TIDR We need the SPRN_TIDR to be set for use with fast thread-wakeup (core- to-core wakeup) and also with CAPI. Each thread in a process needs to have a unique id within the process. But for now, we assign globally unique thread ids to all threads in the system. Signed-off-by: Sukadev Bhattiprolu Signed-off-by: Philippe Bergheaud Signed-off-by: Christophe Lombard [mpe: Simplify tidr clearing on fork() and ctx switch code] Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/processor.h | 1 + arch/powerpc/include/asm/switch_to.h | 3 + arch/powerpc/kernel/process.c | 116 +++++++++++++++++++++++++++++++++++ 3 files changed, 120 insertions(+) diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index fab7ff8..58cc212 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -329,6 +329,7 @@ struct thread_struct { */ int dscr_inherit; unsigned long ppr; /* used to save/restore SMT priority */ + unsigned long tidr; #endif #ifdef CONFIG_PPC_BOOK3S_64 unsigned long tar; diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index 17c8380..f5da32f 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -91,4 +91,7 @@ static inline void clear_task_ebb(struct task_struct *t) #endif } +extern int set_thread_tidr(struct task_struct *t); +extern void clear_thread_tidr(struct task_struct *t); + #endif /* _ASM_POWERPC_SWITCH_TO_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 4083b73..887ae50 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1136,6 +1136,10 @@ static inline void restore_sprs(struct thread_struct *old_thread, if (old_thread->tar != new_thread->tar) mtspr(SPRN_TAR, new_thread->tar); } + + if (cpu_has_feature(CPU_FTR_ARCH_300) && + old_thread->tidr != new_thread->tidr) + mtspr(SPRN_TIDR, new_thread->tidr); #endif } @@ -1451,6 +1455,116 @@ void flush_thread(void) #endif /* CONFIG_HAVE_HW_BREAKPOINT */ } +#ifdef CONFIG_PPC64 +static DEFINE_SPINLOCK(vas_thread_id_lock); +static DEFINE_IDA(vas_thread_ida); + +/* + * We need to assign a unique thread id to each thread in a process. + * + * This thread id, referred to as TIDR, and separate from the Linux's tgid, + * is intended to be used to direct an ASB_Notify from the hardware to the + * thread, when a suitable event occurs in the system. + * + * One such event is a "paste" instruction in the context of Fast Thread + * Wakeup (aka Core-to-core wake up in the Virtual Accelerator Switchboard + * (VAS) in POWER9. + * + * To get a unique TIDR per process we could simply reuse task_pid_nr() but + * the problem is that task_pid_nr() is not yet available copy_thread() is + * called. Fixing that would require changing more intrusive arch-neutral + * code in code path in copy_process()?. + * + * Further, to assign unique TIDRs within each process, we need an atomic + * field (or an IDR) in task_struct, which again intrudes into the arch- + * neutral code. So try to assign globally unique TIDRs for now. + * + * NOTE: TIDR 0 indicates that the thread does not need a TIDR value. + * For now, only threads that expect to be notified by the VAS + * hardware need a TIDR value and we assign values > 0 for those. + */ +#define MAX_THREAD_CONTEXT ((1 << 16) - 1) +static int assign_thread_tidr(void) +{ + int index; + int err; + +again: + if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL)) + return -ENOMEM; + + spin_lock(&vas_thread_id_lock); + err = ida_get_new_above(&vas_thread_ida, 1, &index); + spin_unlock(&vas_thread_id_lock); + + if (err == -EAGAIN) + goto again; + else if (err) + return err; + + if (index > MAX_THREAD_CONTEXT) { + spin_lock(&vas_thread_id_lock); + ida_remove(&vas_thread_ida, index); + spin_unlock(&vas_thread_id_lock); + return -ENOMEM; + } + + return index; +} + +static void free_thread_tidr(int id) +{ + spin_lock(&vas_thread_id_lock); + ida_remove(&vas_thread_ida, id); + spin_unlock(&vas_thread_id_lock); +} + +/* + * Clear any TIDR value assigned to this thread. + */ +void clear_thread_tidr(struct task_struct *t) +{ + if (!t->thread.tidr) + return; + + if (!cpu_has_feature(CPU_FTR_ARCH_300)) { + WARN_ON_ONCE(1); + return; + } + + mtspr(SPRN_TIDR, 0); + free_thread_tidr(t->thread.tidr); + t->thread.tidr = 0; +} + +void arch_release_task_struct(struct task_struct *t) +{ + clear_thread_tidr(t); +} + +/* + * Assign a unique TIDR (thread id) for task @t and set it in the thread + * structure. For now, we only support setting TIDR for 'current' task. + */ +int set_thread_tidr(struct task_struct *t) +{ + if (!cpu_has_feature(CPU_FTR_ARCH_300)) + return -EINVAL; + + if (t != current) + return -EINVAL; + + t->thread.tidr = assign_thread_tidr(); + if (t->thread.tidr < 0) + return t->thread.tidr; + + mtspr(SPRN_TIDR, t->thread.tidr); + + return 0; +} + +#endif /* CONFIG_PPC64 */ + void release_thread(struct task_struct *t) { @@ -1597,6 +1711,8 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, } if (cpu_has_feature(CPU_FTR_HAS_PPR)) p->thread.ppr = INIT_PPR; + + p->thread.tidr = 0; #endif kregs->nip = ppc_function_entry(f); return 0; -- 2.7.4