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ARM: mm: don't flush icache in switch_mm with hardware broadcasting

PATCH New Will Deacon 1 participant 2 messages Jun 6, 2013

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Arm (32-bit) arm64
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Will Deacon

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#0 lore raw

PATCH 1/2 ARM: mm: don't flush icache in switch_mm with hardware broadcasting

When scheduling an mm on a CPU where it hasn't previously been used, we flush the icache on that CPU so that any code loaded previously on a different core can be safely executed.

For cores with hardware broadcasting of cache maintenance operations, this is clearly unnecessary, since the inner-shareable invalidation in __sync_icache_dcache will affect all CPUs.

This patch conditionalises the icache flush in switch_mm based on cache_ops_need_broadcast().

Acked-by Catalin Marinas <[email protected]>
Reported-by Albin Tonnerre <[email protected]>
Signed-off-by Will Deacon <[email protected]>
---
 arch/arm/include/asm/mmu_context.h | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)
arch/arm/include/asm/mmu_context.h +9 -4
index a7b85e0..2a45c33 100644
@@ -18,6 +18,7 @@
 #include <asm/cacheflush.h>
 #include <asm/cachetype.h>
 #include <asm/proc-fns.h>
+#include <asm/smp_plat.h>
 #include <asm-generic/mm_hooks.h>
 
 void __check_vmalloc_seq(struct mm_struct *mm);

@@ -98,12 +99,16 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 #ifdef CONFIG_MMU
 	unsigned int cpu = smp_processor_id();
 
-#ifdef CONFIG_SMP
-	/* check for possible thread migration */
-	if (!cpumask_empty(mm_cpumask(next)) &&
+	/*
+	 * __sync_icache_dcache doesn't broadcast the I-cache invalidation,
+	 * so check for possible thread migration and invalidate the I-cache
+	 * if we're new to this CPU.
+	 */
+	if (cache_ops_need_broadcast() &&
+	    !cpumask_empty(mm_cpumask(next)) &&
 	    !cpumask_test_cpu(cpu, mm_cpumask(next)))
 		__flush_icache_all();
-#endif
+
 	if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next) {
 		check_and_switch_context(next, tsk);
 		if (cache_is_vivt())
Signature · 1 line
1.8.2.2
author
#1 lore raw

PATCH 2/2 arm64: mm: don't bother invalidating the icache in switch_mm

We don't support software broadcast of cache maintenance operations, so this flush is not required (__sync_icache_dcache will always affect all CPUs).

Signed-off-by Will Deacon <[email protected]>
---
 arch/arm64/include/asm/mmu_context.h | 6 ------
 1 file changed, 6 deletions(-)
arch/arm64/include/asm/mmu_context.h +0 -6
index e2bc385..a9eee33 100644
@@ -151,12 +151,6 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 {
 	unsigned int cpu = smp_processor_id();
 
-#ifdef CONFIG_SMP
-	/* check for possible thread migration */
-	if (!cpumask_empty(mm_cpumask(next)) &&
-	    !cpumask_test_cpu(cpu, mm_cpumask(next)))
-		__flush_icache_all();
-#endif
 	if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next)
 		check_and_switch_context(next, tsk);
 }
Signature · 1 line
1.8.2.2