Suka, Please CC Christophe who as an alternative way of doing this. We ned to get agreement across all users of TIDR/AS_notify...
His patch is here: https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-August/161582.html Mikey On Tue, 2017-08-29 at 19:38 -0700, Sukadev Bhattiprolu wrote: > We need the SPRN_TIDR to be set for use with fast thread-wakeup > (core-to-core wakeup) in VAS. Each user thread that has a receive > window setup and expects to be notified when a sender issues a paste > needs to have a unique SPRN_TIDR value. > > The SPRN_TIDR value only needs to unique within the process but for > now we use a globally unique thread id as described below. > > Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com> > --- > Changelog[v2] > - Michael Ellerman: Use an interface to assign TIDR so it is > assigned to only threads that need it; move assignment to > restore_sprs(). Drop lint from rebase; > > > arch/powerpc/include/asm/processor.h | 4 ++ > arch/powerpc/include/asm/switch_to.h | 3 ++ > arch/powerpc/kernel/process.c | 97 > ++++++++++++++++++++++++++++++++++++ > 3 files changed, 104 insertions(+) > > diff --git a/arch/powerpc/include/asm/processor.h > b/arch/powerpc/include/asm/processor.h > index fab7ff8..bf6ba63 100644 > --- a/arch/powerpc/include/asm/processor.h > +++ b/arch/powerpc/include/asm/processor.h > @@ -232,6 +232,10 @@ struct debug_reg { > struct thread_struct { > unsigned long ksp; /* Kernel stack pointer */ > > +#ifdef CONFIG_PPC_VAS > + unsigned long tidr; > +#endif > + > #ifdef CONFIG_PPC64 > unsigned long ksp_vsid; > #endif > diff --git a/arch/powerpc/include/asm/switch_to.h > b/arch/powerpc/include/asm/switch_to.h > index 17c8380..4962455 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 void 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 1f0fd36..13abb22 100644 > --- a/arch/powerpc/kernel/process.c > +++ b/arch/powerpc/kernel/process.c > @@ -1132,6 +1132,10 @@ static inline void restore_sprs(struct thread_struct > *old_thread, > mtspr(SPRN_TAR, new_thread->tar); > } > #endif > +#ifdef CONFIG_PPC_VAS > + if (old_thread->tidr != new_thread->tidr) > + mtspr(SPRN_TIDR, new_thread->tidr); > +#endif > } > > #ifdef CONFIG_PPC_BOOK3S_64 > @@ -1446,9 +1450,97 @@ void flush_thread(void) > #endif /* CONFIG_HAVE_HW_BREAKPOINT */ > } > > +#ifdef CONFIG_PPC_VAS > +static DEFINE_SPINLOCK(vas_thread_id_lock); > +static DEFINE_IDA(vas_thread_ida); > + > +/* > + * We need to assign an unique thread id to each thread in a process. This > + * thread id is intended to be used with the Fast Thread-wakeup (aka Core- > + * to-core wakeup) mechanism being implemented on top of Virtual Accelerator > + * Switchboard (VAS). > + * > + * To get a unique thread-id per process we could simply use task_pid_nr() > + * but the problem is that task_pid_nr() is not yet available for the thread > + * when copy_thread() is called. Fixing that would require changing more > + * intrusive arch-neutral code in code path in copy_process()?. > + * > + * Further, to assign unique thread ids 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 thraed ids 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 << 15) - 2) > +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); > +} > + > +void clear_thread_tidr(struct task_struct *t) > +{ > + if (t->thread.tidr) { > + free_thread_tidr(t->thread.tidr); > + t->thread.tidr = 0; > + mtspr(SPRN_TIDR, 0); > + } > +} > + > +/* > + * Assign an unique thread id for this thread and set it in the > + * thread structure. For now, we need this interface only for > + * the current task. > + */ > +void set_thread_tidr(struct task_struct *t) > +{ > + WARN_ON(t != current); > + t->thread.tidr = assign_thread_tidr(); > + mtspr(SPRN_TIDR, t->thread.tidr); > +} > + > +#endif /* CONFIG_PPC_VAS */ > + > + > void > release_thread(struct task_struct *t) > { > +#ifdef CONFIG_PPC_VAS > + clear_thread_tidr(t); > +#endif > } > > /* > @@ -1474,6 +1566,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct > task_struct *src) > > clear_task_ebb(dst); > > + dst->thread.tidr = 0; > + > return 0; > } > > @@ -1584,6 +1678,9 @@ int copy_thread(unsigned long clone_flags, unsigned long > usp, > #endif > > setup_ksp_vsid(p, sp); > +#ifdef CONFIG_PPC_VAS > + p->thread.tidr = 0; > +#endif > > #ifdef CONFIG_PPC64 > if (cpu_has_feature(CPU_FTR_DSCR)) {
