From e4c0fc5f72bca11432297168338aef46c12793a4 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Fri, 9 Jun 2017 01:36:06 +1000
Subject: [PATCH] powerpc/64s: Leave interrupts hard enabled in context switch
for radix
References: bsc#1055186, fate#323286
Patch-mainline: v4.13-rc1
Git-commit: e4c0fc5f72bca11432297168338aef46c12793a4
Commit 4387e9ff25 ("[POWERPC] Fix PMU + soft interrupt disable bug")
hard disabled interrupts over the low level context switch, because
the SLB management can't cope with a PMU interrupt accesing the stack
in that window.
Radix based kernel mapping does not use the SLB so it does not require
interrupts hard disabled here.
This is worth 1-2% in context switch performance on POWER9.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/entry_64.S | 8 ++++++++
arch/powerpc/kernel/process.c | 14 ++++++++------
2 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 6f70ea821a07..91f9fdc2d027 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -607,6 +607,14 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
top of the kernel stack. */
addi r7,r7,THREAD_SIZE-SWITCH_FRAME_SIZE
+ /*
+ * PMU interrupts in radix may come in here. They will use r1, not
+ * PACAKSAVE, so this stack switch will not cause a problem. They
+ * will store to the process stack, which may then be migrated to
+ * another CPU. However the rq lock release on this CPU paired with
+ * the rq lock acquire on the new CPU before the stack becomes
+ * active on the new CPU, will order those stores.
+ */
mr r1,r8 /* start using new stack pointer */
std r7,PACAKSAVE(r13)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 5cbb8b1faf7e..45faa9a32a01 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1199,12 +1199,14 @@ struct task_struct *__switch_to(struct task_struct *prev,
__switch_to_tm(prev, new);
- /*
- * 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();
+ if (!radix_enabled()) {
+ /*
+ * 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
--
2.10.2