[PATCHv8 4/5] powerpc/cpu: Skip impossible cpu during iteration on a core

[Pingfan Liu]

The threads in a core have equal status, so the code introduces a for
loop pattern to execute the same task on each thread:
    for (i = first_thread; i < first_thread + threads_per_core; i++)

Now that some threads may not be in the cpu_possible_mask, the iteration
skips those threads by checking the mask. In this way, the unpopulated
pcpu struct can be skipped and left unaccessed.

Signed-off-by: Pingfan Liu <piliu at redhat.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Nicholas Piggin <npiggin at gmail.com>
Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
Cc: Wen Xiong <wenxiong at linux.ibm.com>
Cc: Baoquan He <bhe at redhat.com>
Cc: Ming Lei <ming.lei at redhat.com>
Cc: kexec at lists.infradead.org
To: linuxppc-dev at lists.ozlabs.org
---
 arch/powerpc/include/asm/cputhreads.h    |  6 +++++
 arch/powerpc/kernel/smp.c                |  2 +-
 arch/powerpc/kvm/book3s_hv.c             |  7 ++----
 arch/powerpc/platforms/powernv/idle.c    | 32 ++++++++++++------------
 arch/powerpc/platforms/powernv/subcore.c |  5 +++-
 5 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/include/asm/cputhreads.h b/arch/powerpc/include/asm/cputhreads.h
index f26c430f3982..fdb71ff7f6a9 100644
--- a/arch/powerpc/include/asm/cputhreads.h
+++ b/arch/powerpc/include/asm/cputhreads.h
@@ -65,6 +65,12 @@ static inline int cpu_last_thread_sibling(int cpu)
 	return cpu | (threads_per_core - 1);
 }
 
+#define for_each_possible_cpu_in_core(start, iter)			\
+	for (iter = start; iter < start + threads_per_core; iter++)	\
+		if (unlikely(!cpu_possible(iter)))			\
+			continue;					\
+		else
+
 /*
  * tlb_thread_siblings are siblings which share a TLB. This is not
  * architected, is not something a hypervisor could emulate and a future
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index fbbb695bae3d..2936f7a2240d 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -933,7 +933,7 @@ static int __init update_mask_from_threadgroup(cpumask_var_t *mask, struct threa
 
 	zalloc_cpumask_var_node(mask, GFP_KERNEL, cpu_to_node(cpu));
 
-	for (i = first_thread; i < first_thread + threads_per_core; i++) {
+	for_each_possible_cpu_in_core(first_thread, i) {
 		int i_group_start = get_cpu_thread_group_start(i, tg);
 
 		if (unlikely(i_group_start == -1)) {
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 130bafdb1430..ff4b3f8affba 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -6235,12 +6235,9 @@ static int kvm_init_subcore_bitmap(void)
 			return -ENOMEM;
 
 
-		for (j = 0; j < threads_per_core; j++) {
-			int cpu = first_cpu + j;
-
-			paca_ptrs[cpu]->sibling_subcore_state =
+		for_each_possible_cpu_in_core(first_cpu, j)
+			paca_ptrs[j]->sibling_subcore_state =
 						sibling_subcore_state;
-		}
 	}
 	return 0;
 }
diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index ad41dffe4d92..79d81ce5cf4c 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -823,36 +823,36 @@ void pnv_power9_force_smt4_catch(void)
 
 	cpu = smp_processor_id();
 	cpu0 = cpu & ~(threads_per_core - 1);
-	for (thr = 0; thr < threads_per_core; ++thr) {
-		if (cpu != cpu0 + thr)
-			atomic_inc(&paca_ptrs[cpu0+thr]->dont_stop);
+	for_each_possible_cpu_in_core(cpu0, thr) {
+		if (cpu != thr)
+			atomic_inc(&paca_ptrs[thr]->dont_stop);
 	}
 	/* order setting dont_stop vs testing requested_psscr */
 	smp_mb();
-	for (thr = 0; thr < threads_per_core; ++thr) {
-		if (!paca_ptrs[cpu0+thr]->requested_psscr)
+	for_each_possible_cpu_in_core(cpu0, thr) {
+		if (!paca_ptrs[thr]->requested_psscr)
 			++awake_threads;
 		else
-			poke_threads |= (1 << thr);
+			poke_threads |= (1 << (thr - cpu0));
 	}
 
 	/* If at least 3 threads are awake, the core is in SMT4 already */
 	if (awake_threads < need_awake) {
 		/* We have to wake some threads; we'll use msgsnd */
-		for (thr = 0; thr < threads_per_core; ++thr) {
-			if (poke_threads & (1 << thr)) {
+		for_each_possible_cpu_in_core(cpu0, thr) {
+			if (poke_threads & (1 << (thr - cpu0))) {
 				ppc_msgsnd_sync();
 				ppc_msgsnd(PPC_DBELL_MSGTYPE, 0,
-					   paca_ptrs[cpu0+thr]->hw_cpu_id);
+					   paca_ptrs[thr]->hw_cpu_id);
 			}
 		}
 		/* now spin until at least 3 threads are awake */
 		do {
-			for (thr = 0; thr < threads_per_core; ++thr) {
-				if ((poke_threads & (1 << thr)) &&
-				    !paca_ptrs[cpu0+thr]->requested_psscr) {
+			for_each_possible_cpu_in_core(cpu0, thr) {
+				if ((poke_threads & (1 << (thr - cpu0))) &&
+				    !paca_ptrs[thr]->requested_psscr) {
 					++awake_threads;
-					poke_threads &= ~(1 << thr);
+					poke_threads &= ~(1 << (thr - cpu0));
 				}
 			}
 		} while (awake_threads < need_awake);
@@ -868,9 +868,9 @@ void pnv_power9_force_smt4_release(void)
 	cpu0 = cpu & ~(threads_per_core - 1);
 
 	/* clear all the dont_stop flags */
-	for (thr = 0; thr < threads_per_core; ++thr) {
-		if (cpu != cpu0 + thr)
-			atomic_dec(&paca_ptrs[cpu0+thr]->dont_stop);
+	for_each_possible_cpu_in_core(cpu0, thr) {
+		if (cpu != thr)
+			atomic_dec(&paca_ptrs[thr]->dont_stop);
 	}
 }
 EXPORT_SYMBOL_GPL(pnv_power9_force_smt4_release);
diff --git a/arch/powerpc/platforms/powernv/subcore.c b/arch/powerpc/platforms/powernv/subcore.c
index 191424468f10..b229115c8c0f 100644
--- a/arch/powerpc/platforms/powernv/subcore.c
+++ b/arch/powerpc/platforms/powernv/subcore.c
@@ -151,9 +151,12 @@ static void wait_for_sync_step(int step)
 {
 	int i, cpu = smp_processor_id();
 
-	for (i = cpu + 1; i < cpu + threads_per_core; i++)
+	for_each_possible_cpu_in_core(cpu, i) {
+		if (i == cpu)
+			continue;
 		while(per_cpu(split_state, i).step < step)
 			barrier();
+	}
 
 	/* Order the wait loop vs any subsequent loads/stores. */
 	mb();
-- 
2.31.1