arch/powerpc/include/asm/mmu_context.h

   1 #ifndef __ASM_POWERPC_MMU_CONTEXT_H
   2 #define __ASM_POWERPC_MMU_CONTEXT_H
   3 #ifdef __KERNEL__
   4
   5 #include <asm/mmu.h>
   6 #include <asm/cputable.h>
   7 #include <asm-generic/mm_hooks.h>
   8
   9 #ifndef CONFIG_PPC64
  10 #include <asm/atomic.h>
  11 #include <linux/bitops.h>
  12
  13 /*
  14  * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
  15  * (virtual segment identifiers) for each context.  Although the
  16  * hardware supports 24-bit VSIDs, and thus >1 million contexts,
  17  * we only use 32,768 of them.  That is ample, since there can be
  18  * at most around 30,000 tasks in the system anyway, and it means
  19  * that we can use a bitmap to indicate which contexts are in use.
  20  * Using a bitmap means that we entirely avoid all of the problems
  21  * that we used to have when the context number overflowed,
  22  * particularly on SMP systems.
  23  *  -- paulus.
  24  */
  25
  26 /*
  27  * This function defines the mapping from contexts to VSIDs (virtual
  28  * segment IDs).  We use a skew on both the context and the high 4 bits
  29  * of the 32-bit virtual address (the "effective segment ID") in order
  30  * to spread out the entries in the MMU hash table.  Note, if this
  31  * function is changed then arch/ppc/mm/hashtable.S will have to be
  32  * changed to correspond.
  33  */
  34 #define CTX_TO_VSID(ctx, va)    (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
  35                                  & 0xffffff)
  36
  37 /*
  38    The MPC8xx has only 16 contexts.  We rotate through them on each
  39    task switch.  A better way would be to keep track of tasks that
  40    own contexts, and implement an LRU usage.  That way very active
  41    tasks don't always have to pay the TLB reload overhead.  The
  42    kernel pages are mapped shared, so the kernel can run on behalf
  43    of any task that makes a kernel entry.  Shared does not mean they
  44    are not protected, just that the ASID comparison is not performed.
  45         -- Dan
  46
  47    The IBM4xx has 256 contexts, so we can just rotate through these
  48    as a way of "switching" contexts.  If the TID of the TLB is zero,
  49    the PID/TID comparison is disabled, so we can use a TID of zero
  50    to represent all kernel pages as shared among all contexts.
  51         -- Dan
  52  */
  53
  54 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
  55 {
  56 }
  57
  58 #ifdef CONFIG_8xx
  59 #define NO_CONTEXT              16
  60 #define LAST_CONTEXT            15
  61 #define FIRST_CONTEXT           0
  62
  63 #elif defined(CONFIG_4xx)
  64 #define NO_CONTEXT              256
  65 #define LAST_CONTEXT            255
  66 #define FIRST_CONTEXT           1
  67
  68 #elif defined(CONFIG_E200) || defined(CONFIG_E500)
  69 #define NO_CONTEXT              256
  70 #define LAST_CONTEXT            255
  71 #define FIRST_CONTEXT           1
  72
  73 #else
  74
  75 /* PPC 6xx, 7xx CPUs */
  76 #define NO_CONTEXT              ((unsigned long) -1)
  77 #define LAST_CONTEXT            32767
  78 #define FIRST_CONTEXT           1
  79 #endif
  80
  81 /*
  82  * Set the current MMU context.
  83  * On 32-bit PowerPCs (other than the 8xx embedded chips), this is done by
  84  * loading up the segment registers for the user part of the address space.
  85  *
  86  * Since the PGD is immediately available, it is much faster to simply
  87  * pass this along as a second parameter, which is required for 8xx and
  88  * can be used for debugging on all processors (if you happen to have
  89  * an Abatron).
  90  */
  91 extern void set_context(unsigned long contextid, pgd_t *pgd);
  92
  93 /*
  94  * Bitmap of contexts in use.
  95  * The size of this bitmap is LAST_CONTEXT + 1 bits.
  96  */
  97 extern unsigned long context_map[];
  98
  99 /*
 100  * This caches the next context number that we expect to be free.
 101  * Its use is an optimization only, we can't rely on this context
 102  * number to be free, but it usually will be.
 103  */
 104 extern unsigned long next_mmu_context;
 105
 106 /*
 107  * If we don't have sufficient contexts to give one to every task
 108  * that could be in the system, we need to be able to steal contexts.
 109  * These variables support that.
 110  */
 111 #if LAST_CONTEXT < 30000
 112 #define FEW_CONTEXTS    1
 113 extern atomic_t nr_free_contexts;
 114 extern struct mm_struct *context_mm[LAST_CONTEXT+1];
 115 extern void steal_context(void);
 116 #endif
 117
 118 /*
 119  * Get a new mmu context for the address space described by `mm'.
 120  */
 121 static inline void get_mmu_context(struct mm_struct *mm)
 122 {
 123         unsigned long ctx;
 124
 125         if (mm->context.id != NO_CONTEXT)
 126                 return;
 127 #ifdef FEW_CONTEXTS
 128         while (atomic_dec_if_positive(&nr_free_contexts) < 0)
 129                 steal_context();
 130 #endif
 131         ctx = next_mmu_context;
 132         while (test_and_set_bit(ctx, context_map)) {
 133                 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
 134                 if (ctx > LAST_CONTEXT)
 135                         ctx = 0;
 136         }
 137         next_mmu_context = (ctx + 1) & LAST_CONTEXT;
 138         mm->context.id = ctx;
 139 #ifdef FEW_CONTEXTS
 140         context_mm[ctx] = mm;
 141 #endif
 142 }
 143
 144 /*
 145  * Set up the context for a new address space.
 146  */
 147 static inline int init_new_context(struct task_struct *t, struct mm_struct *mm)
 148 {
 149         mm->context.id = NO_CONTEXT;
 150         return 0;
 151 }
 152
 153 /*
 154  * We're finished using the context for an address space.
 155  */
 156 static inline void destroy_context(struct mm_struct *mm)
 157 {
 158         preempt_disable();
 159         if (mm->context.id != NO_CONTEXT) {
 160                 clear_bit(mm->context.id, context_map);
 161                 mm->context.id = NO_CONTEXT;
 162 #ifdef FEW_CONTEXTS
 163                 atomic_inc(&nr_free_contexts);
 164 #endif
 165         }
 166         preempt_enable();
 167 }
 168
 169 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 170                              struct task_struct *tsk)
 171 {
 172 #ifdef CONFIG_ALTIVEC
 173         if (cpu_has_feature(CPU_FTR_ALTIVEC))
 174         asm volatile ("dssall;\n"
 175 #ifndef CONFIG_POWER4
 176          "sync;\n" /* G4 needs a sync here, G5 apparently not */
 177 #endif
 178          : : );
 179 #endif /* CONFIG_ALTIVEC */
 180
 181         tsk->thread.pgdir = next->pgd;
 182
 183         if (!cpu_isset(smp_processor_id(), next->cpu_vm_mask))
 184                 cpu_set(smp_processor_id(), next->cpu_vm_mask);
 185
 186         /* No need to flush userspace segments if the mm doesnt change */
 187         if (prev == next)
 188                 return;
 189
 190         /* Setup new userspace context */
 191         get_mmu_context(next);
 192         set_context(next->context.id, next->pgd);
 193 }
 194
 195 #define deactivate_mm(tsk,mm)   do { } while (0)
 196
 197 /*
 198  * After we have set current->mm to a new value, this activates
 199  * the context for the new mm so we see the new mappings.
 200  */
 201 #define activate_mm(active_mm, mm)   switch_mm(active_mm, mm, current)
 202
 203 extern void mmu_context_init(void);
 204
 205
 206 #else
 207
 208 #include <linux/kernel.h>
 209 #include <linux/mm.h>
 210 #include <linux/sched.h>
 211
 212 /*
 213  * Copyright (C) 2001 PPC 64 Team, IBM Corp
 214  *
 215  * This program is free software; you can redistribute it and/or
 216  * modify it under the terms of the GNU General Public License
 217  * as published by the Free Software Foundation; either version
 218  * 2 of the License, or (at your option) any later version.
 219  */
 220
 221 static inline void enter_lazy_tlb(struct mm_struct *mm,
 222                                   struct task_struct *tsk)
 223 {
 224 }
 225
 226 /*
 227  * The proto-VSID space has 2^35 - 1 segments available for user mappings.
 228  * Each segment contains 2^28 bytes.  Each context maps 2^44 bytes,
 229  * so we can support 2^19-1 contexts (19 == 35 + 28 - 44).
 230  */
 231 #define NO_CONTEXT      0
 232 #define MAX_CONTEXT     ((1UL << 19) - 1)
 233
 234 extern int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
 235 extern void destroy_context(struct mm_struct *mm);
 236
 237 extern void switch_stab(struct task_struct *tsk, struct mm_struct *mm);
 238 extern void switch_slb(struct task_struct *tsk, struct mm_struct *mm);
 239
 240 /*
 241  * switch_mm is the entry point called from the architecture independent
 242  * code in kernel/sched.c
 243  */
 244 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 245                              struct task_struct *tsk)
 246 {
 247         if (!cpu_isset(smp_processor_id(), next->cpu_vm_mask))
 248                 cpu_set(smp_processor_id(), next->cpu_vm_mask);
 249
 250         /* No need to flush userspace segments if the mm doesnt change */
 251         if (prev == next)
 252                 return;
 253
 254 #ifdef CONFIG_ALTIVEC
 255         if (cpu_has_feature(CPU_FTR_ALTIVEC))
 256                 asm volatile ("dssall");
 257 #endif /* CONFIG_ALTIVEC */
 258
 259         if (cpu_has_feature(CPU_FTR_SLB))
 260                 switch_slb(tsk, next);
 261         else
 262                 switch_stab(tsk, next);
 263 }
 264
 265 #define deactivate_mm(tsk,mm)   do { } while (0)
 266
 267 /*
 268  * After we have set current->mm to a new value, this activates
 269  * the context for the new mm so we see the new mappings.
 270  */
 271 static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
 272 {
 273         unsigned long flags;
 274
 275         local_irq_save(flags);
 276         switch_mm(prev, next, current);
 277         local_irq_restore(flags);
 278 }
 279
 280 #endif /* CONFIG_PPC64 */
 281 #endif /* __KERNEL__ */
 282 #endif /* __ASM_POWERPC_MMU_CONTEXT_H */