arch/arc/include/asm/mmu_context.h

   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 check 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 */