[PATCH 1/6] powernv:idle: Correctly initialize core_idle_state_ptr

From: Gautham R. Shenoy
Date: Tue May 16 2017 - 04:51:25 EST


From: "Gautham R. Shenoy" <ego@xxxxxxxxxxxxxxxxxx>

The lower 8 bits of core_idle_state_ptr tracks the number of non-idle
threads in the core. This is supposed to be initialized to bit-map
corresponding to the threads_per_core. However, currently it is
initialized to PNV_CORE_IDLE_THREAD_BITS (0xFF). This is correct for
POWER8 which has 8 threads per core, but not for POWER9 which has 4
threads per core.

As a result, on POWER9, core_idle_state_ptr gets initialized to
0xFF. In case when all the threads of the core are idle, the bits
corresponding tracking the idle-threads are non-zero. As a result, the
idle entry/exit code fails to save/restore per-core hypervisor state
since it assumes that there are threads in the cores which are still
active.

Fix this by correctly initializing the lower bits of the
core_idle_state_ptr on the basis of threads_per_core.

Signed-off-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>
---
arch/powerpc/platforms/powernv/idle.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 445f30a..84eb9bc 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -96,15 +96,24 @@ static void pnv_alloc_idle_core_states(void)
u32 *core_idle_state;

/*
- * core_idle_state - First 8 bits track the idle state of each thread
- * of the core. The 8th bit is the lock bit. Initially all thread bits
- * are set. They are cleared when the thread enters deep idle state
- * like sleep and winkle. Initially the lock bit is cleared.
- * The lock bit has 2 purposes
- * a. While the first thread is restoring core state, it prevents
- * other threads in the core from switching to process context.
- * b. While the last thread in the core is saving the core state, it
- * prevents a different thread from waking up.
+ * core_idle_state - The lower 8 bits track the idle state of
+ * each thread of the core.
+ *
+ * The most significant bit is the lock bit.
+ *
+ * Initially all the bits corresponding to threads_per_core
+ * are set. They are cleared when the thread enters deep idle
+ * state like sleep and winkle/stop.
+ *
+ * Initially the lock bit is cleared. The lock bit has 2
+ * purposes:
+ * a. While the first thread in the core waking up from
+ * idle is restoring core state, it prevents other
+ * threads in the core from switching to process
+ * context.
+ * b. While the last thread in the core is saving the
+ * core state, it prevents a different thread from
+ * waking up.
*/
for (i = 0; i < nr_cores; i++) {
int first_cpu = i * threads_per_core;
@@ -112,7 +121,7 @@ static void pnv_alloc_idle_core_states(void)
size_t paca_ptr_array_size;

core_idle_state = kmalloc_node(sizeof(u32), GFP_KERNEL, node);
- *core_idle_state = PNV_CORE_IDLE_THREAD_BITS;
+ *core_idle_state = (1 << threads_per_core) - 1;
paca_ptr_array_size = (threads_per_core *
sizeof(struct paca_struct *));

--
1.8.3.1