1 /* 2 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 * 8 * vineetg: May 2011 9 * -Refactored get_new_mmu_context( ) to only handle live-mm. 10 * retiring-mm handled in other hooks 11 * 12 * Vineetg: March 25th, 2008: Bug #92690 13 * -Major rewrite of Core ASID allocation routine get_new_mmu_context 14 * 15 * Amit Bhor, Sameer Dhavale: Codito Technologies 2004 16 */ 17 18 #ifndef _ASM_ARC_MMU_CONTEXT_H 19 #define _ASM_ARC_MMU_CONTEXT_H 20 21 #include <asm/arcregs.h> 22 #include <asm/tlb.h> 23 24 #include <asm-generic/mm_hooks.h> 25 26 /* ARC700 ASID Management 27 * 28 * ARC MMU provides 8-bit ASID (0..255) to TAG TLB entries, allowing entries 29 * with same vaddr (different tasks) to co-exit. This provides for 30 * "Fast Context Switch" i.e. no TLB flush on ctxt-switch 31 * 32 * Linux assigns each task a unique ASID. A simple round-robin allocation 33 * of H/w ASID is done using software tracker @asid_cpu. 34 * When it reaches max 255, the allocation cycle starts afresh by flushing 35 * the entire TLB and wrapping ASID back to zero. 36 * 37 * A new allocation cycle, post rollover, could potentially reassign an ASID 38 * to a different task. Thus the rule is to refresh the ASID in a new cycle. 39 * The 32 bit @asid_cpu (and mm->asid) have 8 bits MMU PID and rest 24 bits 40 * serve as cycle/generation indicator and natural 32 bit unsigned math 41 * automagically increments the generation when lower 8 bits rollover. 42 */ 43 44 #define MM_CTXT_ASID_MASK 0x000000ff /* MMU PID reg :8 bit PID */ 45 #define MM_CTXT_CYCLE_MASK (~MM_CTXT_ASID_MASK) 46 47 #define MM_CTXT_FIRST_CYCLE (MM_CTXT_ASID_MASK + 1) 48 #define MM_CTXT_NO_ASID 0UL 49 50 #define asid_mm(mm, cpu) mm->context.asid[cpu] 51 #define hw_pid(mm, cpu) (asid_mm(mm, cpu) & MM_CTXT_ASID_MASK) 52 53 DECLARE_PER_CPU(unsigned int, asid_cache); 54 #define asid_cpu(cpu) per_cpu(asid_cache, cpu) 55 56 /* 57 * Get a new ASID if task doesn't have a valid one (unalloc or from prev cycle) 58 * Also set the MMU PID register to existing/updated ASID 59 */ 60 static inline void get_new_mmu_context(struct mm_struct *mm) 61 { 62 const unsigned int cpu = smp_processor_id(); 63 unsigned long flags; 64 65 local_irq_save(flags); 66 67 /* 68 * Move to new ASID if it was not from current alloc-cycle/generation. 69 * This is done by ensuring that the generation bits in both mm->ASID 70 * and cpu's ASID counter are exactly same. 71 * 72 * Note: Callers needing new ASID unconditionally, independent of 73 * generation, e.g. local_flush_tlb_mm() for forking parent, 74 * first need to destroy the context, setting it to invalid 75 * value. 76 */ 77 if (!((asid_mm(mm, cpu) ^ asid_cpu(cpu)) & MM_CTXT_CYCLE_MASK)) 78 goto set_hw; 79 80 /* move to new ASID and handle rollover */ 81 if (unlikely(!(++asid_cpu(cpu) & MM_CTXT_ASID_MASK))) { 82 83 local_flush_tlb_all(); 84 85 /* 86 * Above checke for rollover of 8 bit ASID in 32 bit container. 87 * If the container itself wrapped around, set it to a non zero 88 * "generation" to distinguish from no context 89 */ 90 if (!asid_cpu(cpu)) 91 asid_cpu(cpu) = MM_CTXT_FIRST_CYCLE; 92 } 93 94 /* Assign new ASID to tsk */ 95 asid_mm(mm, cpu) = asid_cpu(cpu); 96 97 set_hw: 98 write_aux_reg(ARC_REG_PID, hw_pid(mm, cpu) | MMU_ENABLE); 99 100 local_irq_restore(flags); 101 } 102 103 /* 104 * Initialize the context related info for a new mm_struct 105 * instance. 106 */ 107 static inline int 108 init_new_context(struct task_struct *tsk, struct mm_struct *mm) 109 { 110 int i; 111 112 for_each_possible_cpu(i) 113 asid_mm(mm, i) = MM_CTXT_NO_ASID; 114 115 return 0; 116 } 117 118 static inline void destroy_context(struct mm_struct *mm) 119 { 120 unsigned long flags; 121 122 /* Needed to elide CONFIG_DEBUG_PREEMPT warning */ 123 local_irq_save(flags); 124 asid_mm(mm, smp_processor_id()) = MM_CTXT_NO_ASID; 125 local_irq_restore(flags); 126 } 127 128 /* Prepare the MMU for task: setup PID reg with allocated ASID 129 If task doesn't have an ASID (never alloc or stolen, get a new ASID) 130 */ 131 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, 132 struct task_struct *tsk) 133 { 134 const int cpu = smp_processor_id(); 135 136 /* 137 * Note that the mm_cpumask is "aggregating" only, we don't clear it 138 * for the switched-out task, unlike some other arches. 139 * It is used to enlist cpus for sending TLB flush IPIs and not sending 140 * it to CPUs where a task once ran-on, could cause stale TLB entry 141 * re-use, specially for a multi-threaded task. 142 * e.g. T1 runs on C1, migrates to C3. T2 running on C2 munmaps. 143 * For a non-aggregating mm_cpumask, IPI not sent C1, and if T1 144 * were to re-migrate to C1, it could access the unmapped region 145 * via any existing stale TLB entries. 146 */ 147 cpumask_set_cpu(cpu, mm_cpumask(next)); 148 149 #ifndef CONFIG_SMP 150 /* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */ 151 write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd); 152 #endif 153 154 get_new_mmu_context(next); 155 } 156 157 /* 158 * Called at the time of execve() to get a new ASID 159 * Note the subtlety here: get_new_mmu_context() behaves differently here 160 * vs. in switch_mm(). Here it always returns a new ASID, because mm has 161 * an unallocated "initial" value, while in latter, it moves to a new ASID, 162 * only if it was unallocated 163 */ 164 #define activate_mm(prev, next) switch_mm(prev, next, NULL) 165 166 /* it seemed that deactivate_mm( ) is a reasonable place to do book-keeping 167 * for retiring-mm. However destroy_context( ) still needs to do that because 168 * between mm_release( ) = >deactive_mm( ) and 169 * mmput => .. => __mmdrop( ) => destroy_context( ) 170 * there is a good chance that task gets sched-out/in, making it's ASID valid 171 * again (this teased me for a whole day). 172 */ 173 #define deactivate_mm(tsk, mm) do { } while (0) 174 175 #define enter_lazy_tlb(mm, tsk) 176 177 #endif /* __ASM_ARC_MMU_CONTEXT_H */ 178