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_cache. 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_cache (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 hw_pid(mm) (mm->context.asid & MM_CTXT_ASID_MASK) 51 52 extern unsigned int asid_cache; 53 54 /* 55 * Get a new ASID if task doesn't have a valid one (unalloc or from prev cycle) 56 * Also set the MMU PID register to existing/updated ASID 57 */ 58 static inline void get_new_mmu_context(struct mm_struct *mm) 59 { 60 unsigned long flags; 61 62 local_irq_save(flags); 63 64 /* 65 * Move to new ASID if it was not from current alloc-cycle/generation. 66 * This is done by ensuring that the generation bits in both mm->ASID 67 * and cpu's ASID counter are exactly same. 68 * 69 * Note: Callers needing new ASID unconditionally, independent of 70 * generation, e.g. local_flush_tlb_mm() for forking parent, 71 * first need to destroy the context, setting it to invalid 72 * value. 73 */ 74 if (!((mm->context.asid ^ asid_cache) & MM_CTXT_CYCLE_MASK)) 75 goto set_hw; 76 77 /* move to new ASID and handle rollover */ 78 if (unlikely(!(++asid_cache & MM_CTXT_ASID_MASK))) { 79 80 flush_tlb_all(); 81 82 /* 83 * Above checke for rollover of 8 bit ASID in 32 bit container. 84 * If the container itself wrapped around, set it to a non zero 85 * "generation" to distinguish from no context 86 */ 87 if (!asid_cache) 88 asid_cache = MM_CTXT_FIRST_CYCLE; 89 } 90 91 /* Assign new ASID to tsk */ 92 mm->context.asid = asid_cache; 93 94 set_hw: 95 write_aux_reg(ARC_REG_PID, hw_pid(mm) | MMU_ENABLE); 96 97 local_irq_restore(flags); 98 } 99 100 /* 101 * Initialize the context related info for a new mm_struct 102 * instance. 103 */ 104 static inline int 105 init_new_context(struct task_struct *tsk, struct mm_struct *mm) 106 { 107 mm->context.asid = MM_CTXT_NO_ASID; 108 return 0; 109 } 110 111 /* Prepare the MMU for task: setup PID reg with allocated ASID 112 If task doesn't have an ASID (never alloc or stolen, get a new ASID) 113 */ 114 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, 115 struct task_struct *tsk) 116 { 117 #ifndef CONFIG_SMP 118 /* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */ 119 write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd); 120 #endif 121 122 get_new_mmu_context(next); 123 } 124 125 /* 126 * Called at the time of execve() to get a new ASID 127 * Note the subtlety here: get_new_mmu_context() behaves differently here 128 * vs. in switch_mm(). Here it always returns a new ASID, because mm has 129 * an unallocated "initial" value, while in latter, it moves to a new ASID, 130 * only if it was unallocated 131 */ 132 #define activate_mm(prev, next) switch_mm(prev, next, NULL) 133 134 static inline void destroy_context(struct mm_struct *mm) 135 { 136 mm->context.asid = MM_CTXT_NO_ASID; 137 } 138 139 /* it seemed that deactivate_mm( ) is a reasonable place to do book-keeping 140 * for retiring-mm. However destroy_context( ) still needs to do that because 141 * between mm_release( ) = >deactive_mm( ) and 142 * mmput => .. => __mmdrop( ) => destroy_context( ) 143 * there is a good chance that task gets sched-out/in, making it's ASID valid 144 * again (this teased me for a whole day). 145 */ 146 #define deactivate_mm(tsk, mm) do { } while (0) 147 148 #define enter_lazy_tlb(mm, tsk) 149 150 #endif /* __ASM_ARC_MMU_CONTEXT_H */ 151