We need the SPRN_TIDR to bet set for use with fast thread-wakeup
(core-to-core wakeup). Each thread in a process needs to have a
unique id within the process but as explained below, for now, we
assign globally unique thread ids to all threads in the system.
Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/processor.h | 4 ++
arch/powerpc/kernel/process.c | 74 ++++++++++++++++++++++++++++++++++++
2 files changed, 78 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/kernel/process.c b/arch/powerpc/kernel/process.c
index 9f3e2c9..6123859 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1213,6 +1213,16 @@ struct task_struct *__switch_to(struct task_struct *prev,
hard_irq_disable();
}
+#ifdef CONFIG_PPC_VAS
+ mtspr(SPRN_TIDR, new->thread.tidr);
+#endif
+ /*
+ * We can't take a PMU exception inside _switch() since there is a
+ * window where the kernel stack SLB and the kernel stack are out
+ * of sync. Hard disable here.
+ */
+ hard_irq_disable();
+
/*
* Call restore_sprs() before calling _switch(). If we move it after
* _switch() then we miss out on calling it for new tasks. The reason
@@ -1449,9 +1459,70 @@ 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.
+ */
+static int assign_thread_id(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_USER_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_id(int id)
+{
+ spin_lock(&vas_thread_id_lock);
+ ida_remove(&vas_thread_ida, id);
+ spin_unlock(&vas_thread_id_lock);
+}
+#endif /* CONFIG_PPC_VAS */
+
+
void
release_thread(struct task_struct *t)
{
+#ifdef CONFIG_PPC_VAS
+ free_thread_id(t->thread.tidr);
+#endif
}
/*
@@ -1587,6 +1658,9 @@ int copy_thread(unsigned long clone_flags, unsigned long
usp,
#endif
setup_ksp_vsid(p, sp);
+#ifdef CONFIG_PPC_VAS
+ p->thread.tidr = assign_thread_id();
+#endif
#ifdef CONFIG_PPC64
if (cpu_has_feature(CPU_FTR_DSCR)) {
--
2.7.4
