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

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
......@@ -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;
......
......@@ -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 */
......@@ -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;
......
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