From c2775b2ee5caca19f661ee2ab5af92462596db71 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 6 Oct 2015 18:46:27 +0100 Subject: [PATCH] arm64: switch_mm: simplify mm and CPU checks switch_mm performs some checks to try and avoid entering the ASID allocator: (1) If we're switching to the init_mm (no user mappings), then simply set a reserved TTBR0 value with no page table (the zero page) (2) If prev == next *and* the mm_cpumask indicates that we've run on this CPU before, then we can skip the allocator. However, there is plenty of redundancy here. With the new ASID allocator, if prev == next, then we know that our ASID is valid and do not need to worry about re-allocation. Consequently, we can drop the mm_cpumask check in (2) and move the prev == next check before the init_mm check, since if prev == next == init_mm then there's nothing to do. Reviewed-by: Catalin Marinas Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/mmu_context.h | 6 ++++-- arch/arm64/mm/context.c | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h index f4c74a951b6c..c0e87898ba96 100644 --- a/arch/arm64/include/asm/mmu_context.h +++ b/arch/arm64/include/asm/mmu_context.h @@ -129,6 +129,9 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next, { unsigned int cpu = smp_processor_id(); + if (prev == next) + return; + /* * init_mm.pgd does not contain any user mappings and it is always * active for kernel addresses in TTBR1. Just set the reserved TTBR0. @@ -138,8 +141,7 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next, return; } - if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next) - check_and_switch_context(next, tsk); + check_and_switch_context(next, cpu); } #define deactivate_mm(tsk,mm) do { } while (0) diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index e902229b1a3d..4b9ec4484e3f 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -166,10 +166,10 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) local_flush_tlb_all(); atomic64_set(&per_cpu(active_asids, cpu), asid); - cpumask_set_cpu(cpu, mm_cpumask(mm)); raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); switch_mm_fastpath: + cpumask_set_cpu(cpu, mm_cpumask(mm)); cpu_switch_mm(mm->pgd, mm); }