include/asm-ppc/mmu_context.h

   1 #ifdef __KERNEL__
   2 #ifndef __PPC_MMU_CONTEXT_H
   3 #define __PPC_MMU_CONTEXT_H
   4
   5 #include <linux/config.h>
   6 #include <asm/atomic.h>
   7 #include <asm/bitops.h>
   8 #include <asm/mmu.h>
   9 #include <asm/cputable.h>
  10
  11 /*
  12  * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
  13  * (virtual segment identifiers) for each context.  Although the
  14  * hardware supports 24-bit VSIDs, and thus >1 million contexts,
  15  * we only use 32,768 of them.  That is ample, since there can be
  16  * at most around 30,000 tasks in the system anyway, and it means
  17  * that we can use a bitmap to indicate which contexts are in use.
  18  * Using a bitmap means that we entirely avoid all of the problems
  19  * that we used to have when the context number overflowed,
  20  * particularly on SMP systems.
  21  *  -- paulus.
  22  */
  23
  24 /*
  25  * This function defines the mapping from contexts to VSIDs (virtual
  26  * segment IDs).  We use a skew on both the context and the high 4 bits
  27  * of the 32-bit virtual address (the "effective segment ID") in order
  28  * to spread out the entries in the MMU hash table.  Note, if this
  29  * function is changed then arch/ppc/mm/hashtable.S will have to be
  30  * changed to correspond.
  31  */
  32 #define CTX_TO_VSID(ctx, va)    (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
  33                                  & 0xffffff)
  34
  35 /*
  36    The MPC8xx has only 16 contexts.  We rotate through them on each
  37    task switch.  A better way would be to keep track of tasks that
  38    own contexts, and implement an LRU usage.  That way very active
  39    tasks don't always have to pay the TLB reload overhead.  The
  40    kernel pages are mapped shared, so the kernel can run on behalf
  41    of any task that makes a kernel entry.  Shared does not mean they
  42    are not protected, just that the ASID comparison is not performed.
  43         -- Dan
  44
  45    The IBM4xx has 256 contexts, so we can just rotate through these
  46    as a way of "switching" contexts.  If the TID of the TLB is zero,
  47    the PID/TID comparison is disabled, so we can use a TID of zero
  48    to represent all kernel pages as shared among all contexts.
  49         -- Dan
  50  */
  51
  52 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
  53 {
  54 }
  55
  56 #ifdef CONFIG_8xx
  57 #define NO_CONTEXT              16
  58 #define LAST_CONTEXT            15
  59 #define FIRST_CONTEXT           0
  60
  61 #elif defined(CONFIG_4xx)
  62 #define NO_CONTEXT              256
  63 #define LAST_CONTEXT            255
  64 #define FIRST_CONTEXT           1
  65
  66 #elif defined(CONFIG_E500)
  67 #define NO_CONTEXT              256
  68 #define LAST_CONTEXT            255
  69 #define FIRST_CONTEXT           1
  70
  71 #else
  72
  73 /* PPC 6xx, 7xx CPUs */
  74 #define NO_CONTEXT              ((mm_context_t) -1)
  75 #define LAST_CONTEXT            32767
  76 #define FIRST_CONTEXT           1
  77 #endif
  78
  79 /*
  80  * Set the current MMU context.
  81  * On 32-bit PowerPCs (other than the 8xx embedded chips), this is done by
  82  * loading up the segment registers for the user part of the address space.
  83  *
  84  * Since the PGD is immediately available, it is much faster to simply
  85  * pass this along as a second parameter, which is required for 8xx and
  86  * can be used for debugging on all processors (if you happen to have
  87  * an Abatron).
  88  */
  89 extern void set_context(mm_context_t context, pgd_t *pgd);
  90
  91 /*
  92  * Bitmap of contexts in use.
  93  * The size of this bitmap is LAST_CONTEXT + 1 bits.
  94  */
  95 extern unsigned long context_map[];
  96
  97 /*
  98  * This caches the next context number that we expect to be free.
  99  * Its use is an optimization only, we can't rely on this context
 100  * number to be free, but it usually will be.
 101  */
 102 extern mm_context_t next_mmu_context;
 103
 104 /*
 105  * If we don't have sufficient contexts to give one to every task
 106  * that could be in the system, we need to be able to steal contexts.
 107  * These variables support that.
 108  */
 109 #if LAST_CONTEXT < 30000
 110 #define FEW_CONTEXTS    1
 111 extern atomic_t nr_free_contexts;
 112 extern struct mm_struct *context_mm[LAST_CONTEXT+1];
 113 extern void steal_context(void);
 114 #endif
 115
 116 /*
 117  * Get a new mmu context for the address space described by `mm'.
 118  */
 119 static inline void get_mmu_context(struct mm_struct *mm)
 120 {
 121         mm_context_t ctx;
 122
 123         if (mm->context != NO_CONTEXT)
 124                 return;
 125 #ifdef FEW_CONTEXTS
 126         while (atomic_dec_if_positive(&nr_free_contexts) < 0)
 127                 steal_context();
 128 #endif
 129         ctx = next_mmu_context;
 130         while (test_and_set_bit(ctx, context_map)) {
 131                 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
 132                 if (ctx > LAST_CONTEXT)
 133                         ctx = 0;
 134         }
 135         next_mmu_context = (ctx + 1) & LAST_CONTEXT;
 136         mm->context = ctx;
 137 #ifdef FEW_CONTEXTS
 138         context_mm[ctx] = mm;
 139 #endif
 140 }
 141
 142 /*
 143  * Set up the context for a new address space.
 144  */
 145 #define init_new_context(tsk,mm)        (((mm)->context = NO_CONTEXT), 0)
 146
 147 /*
 148  * We're finished using the context for an address space.
 149  */
 150 static inline void destroy_context(struct mm_struct *mm)
 151 {
 152         if (mm->context != NO_CONTEXT) {
 153                 clear_bit(mm->context, context_map);
 154                 mm->context = NO_CONTEXT;
 155 #ifdef FEW_CONTEXTS
 156                 atomic_inc(&nr_free_contexts);
 157 #endif
 158         }
 159 }
 160
 161 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 162                              struct task_struct *tsk)
 163 {
 164 #ifdef CONFIG_ALTIVEC
 165         asm volatile (
 166  BEGIN_FTR_SECTION
 167         "dssall;\n"
 168 #ifndef CONFIG_POWER4
 169          "sync;\n" /* G4 needs a sync here, G5 apparently not */
 170 #endif
 171  END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 172          : : );
 173 #endif /* CONFIG_ALTIVEC */
 174
 175         tsk->thread.pgdir = next->pgd;
 176
 177         /* No need to flush userspace segments if the mm doesnt change */
 178         if (prev == next)
 179                 return;
 180
 181         /* Setup new userspace context */
 182         get_mmu_context(next);
 183         set_context(next->context, next->pgd);
 184 }
 185
 186 #define deactivate_mm(tsk,mm)   do { } while (0)
 187
 188 /*
 189  * After we have set current->mm to a new value, this activates
 190  * the context for the new mm so we see the new mappings.
 191  */
 192 #define activate_mm(active_mm, mm)   switch_mm(active_mm, mm, current)
 193
 194 extern void mmu_context_init(void);
 195
 196 #endif /* __PPC_MMU_CONTEXT_H */
 197 #endif /* __KERNEL__ */