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Commit ec233ede authored by Sukadev Bhattiprolu's avatar Sukadev Bhattiprolu Committed by Michael Ellerman
Browse files

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: default avatarSukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: default avatarPhilippe Bergheaud <felix@linux.vnet.ibm.com>
Signed-off-by: default avatarChristophe Lombard <clombard@linux.vnet.ibm.com>
[mpe: Simplify tidr clearing on fork() and ctx switch code]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent ece4e512

arch/powerpc/include/asm/processor.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/include/asm/switch_to.h

+3 −0
Original line number Diff line number Diff line
@@ -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 */

arch/powerpc/kernel/process.c

+116 −0
Original line number Diff line number Diff line
@@ -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;