include/asm-ppc64/mmu_context.h

   1 #ifndef __PPC64_MMU_CONTEXT_H
   2 #define __PPC64_MMU_CONTEXT_H
   3
   4 #include <linux/config.h>
   5 #include <linux/kernel.h>
   6 #include <linux/mm.h>
   7 #include <asm/mmu.h>
   8 #include <asm/cputable.h>
   9
  10 /*
  11  * Copyright (C) 2001 PPC 64 Team, IBM Corp
  12  *
  13  * This program is free software; you can redistribute it and/or
  14  * modify it under the terms of the GNU General Public License
  15  * as published by the Free Software Foundation; either version
  16  * 2 of the License, or (at your option) any later version.
  17  */
  18
  19 /*
  20  * Every architecture must define this function. It's the fastest
  21  * way of searching a 140-bit bitmap where the first 100 bits are
  22  * unlikely to be set. It's guaranteed that at least one of the 140
  23  * bits is cleared.
  24  */
  25 static inline int sched_find_first_bit(unsigned long *b)
  26 {
  27         if (unlikely(b[0]))
  28                 return __ffs(b[0]);
  29         if (unlikely(b[1]))
  30                 return __ffs(b[1]) + 64;
  31         return __ffs(b[2]) + 128;
  32 }
  33
  34 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
  35 {
  36 }
  37
  38 #define NO_CONTEXT      0
  39 #define MAX_CONTEXT     (0x100000-1)
  40
  41 extern int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
  42 extern void destroy_context(struct mm_struct *mm);
  43
  44 extern void switch_stab(struct task_struct *tsk, struct mm_struct *mm);
  45 extern void switch_slb(struct task_struct *tsk, struct mm_struct *mm);
  46
  47 /*
  48  * switch_mm is the entry point called from the architecture independent
  49  * code in kernel/sched.c
  50  */
  51 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
  52                              struct task_struct *tsk)
  53 {
  54         if (!cpu_isset(smp_processor_id(), next->cpu_vm_mask))
  55                 cpu_set(smp_processor_id(), next->cpu_vm_mask);
  56
  57         /* No need to flush userspace segments if the mm doesnt change */
  58         if (prev == next)
  59                 return;
  60
  61 #ifdef CONFIG_ALTIVEC
  62         if (cpu_has_feature(CPU_FTR_ALTIVEC))
  63                 asm volatile ("dssall");
  64 #endif /* CONFIG_ALTIVEC */
  65
  66         if (cpu_has_feature(CPU_FTR_SLB))
  67                 switch_slb(tsk, next);
  68         else
  69                 switch_stab(tsk, next);
  70 }
  71
  72 #define deactivate_mm(tsk,mm)   do { } while (0)
  73
  74 /*
  75  * After we have set current->mm to a new value, this activates
  76  * the context for the new mm so we see the new mappings.
  77  */
  78 static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
  79 {
  80         unsigned long flags;
  81
  82         local_irq_save(flags);
  83         switch_mm(prev, next, current);
  84         local_irq_restore(flags);
  85 }
  86
  87 /* VSID allocation
  88  * ===============
  89  *
  90  * We first generate a 36-bit "proto-VSID".  For kernel addresses this
  91  * is equal to the ESID, for user addresses it is:
  92  *      (context << 15) | (esid & 0x7fff)
  93  *
  94  * The two forms are distinguishable because the top bit is 0 for user
  95  * addresses, whereas the top two bits are 1 for kernel addresses.
  96  * Proto-VSIDs with the top two bits equal to 0b10 are reserved for
  97  * now.
  98  *
  99  * The proto-VSIDs are then scrambled into real VSIDs with the
 100  * multiplicative hash:
 101  *
 102  *      VSID = (proto-VSID * VSID_MULTIPLIER) % VSID_MODULUS
 103  *      where   VSID_MULTIPLIER = 268435399 = 0xFFFFFC7
 104  *              VSID_MODULUS = 2^36-1 = 0xFFFFFFFFF
 105  *
 106  * This scramble is only well defined for proto-VSIDs below
 107  * 0xFFFFFFFFF, so both proto-VSID and actual VSID 0xFFFFFFFFF are
 108  * reserved.  VSID_MULTIPLIER is prime, so in particular it is
 109  * co-prime to VSID_MODULUS, making this a 1:1 scrambling function.
 110  * Because the modulus is 2^n-1 we can compute it efficiently without
 111  * a divide or extra multiply (see below).
 112  *
 113  * This scheme has several advantages over older methods:
 114  *
 115  *      - We have VSIDs allocated for every kernel address
 116  * (i.e. everything above 0xC000000000000000), except the very top
 117  * segment, which simplifies several things.
 118  *
 119  *      - We allow for 15 significant bits of ESID and 20 bits of
 120  * context for user addresses.  i.e. 8T (43 bits) of address space for
 121  * up to 1M contexts (although the page table structure and context
 122  * allocation will need changes to take advantage of this).
 123  *
 124  *      - The scramble function gives robust scattering in the hash
 125  * table (at least based on some initial results).  The previous
 126  * method was more susceptible to pathological cases giving excessive
 127  * hash collisions.
 128  */
 129
 130 /*
 131  * WARNING - If you change these you must make sure the asm
 132  * implementations in slb_allocate(), do_stab_bolted and mmu.h
 133  * (ASM_VSID_SCRAMBLE macro) are changed accordingly.
 134  *
 135  * You'll also need to change the precomputed VSID values in head.S
 136  * which are used by the iSeries firmware.
 137  */
 138
 139 static inline unsigned long vsid_scramble(unsigned long protovsid)
 140 {
 141 #if 0
 142         /* The code below is equivalent to this function for arguments
 143          * < 2^VSID_BITS, which is all this should ever be called
 144          * with.  However gcc is not clever enough to compute the
 145          * modulus (2^n-1) without a second multiply. */
 146         return ((protovsid * VSID_MULTIPLIER) % VSID_MODULUS);
 147 #else /* 1 */
 148         unsigned long x;
 149
 150         x = protovsid * VSID_MULTIPLIER;
 151         x = (x >> VSID_BITS) + (x & VSID_MODULUS);
 152         return (x + ((x+1) >> VSID_BITS)) & VSID_MODULUS;
 153 #endif /* 1 */
 154 }
 155
 156 /* This is only valid for addresses >= KERNELBASE */
 157 static inline unsigned long get_kernel_vsid(unsigned long ea)
 158 {
 159         return vsid_scramble(ea >> SID_SHIFT);
 160 }
 161
 162 /* This is only valid for user addresses (which are below 2^41) */
 163 static inline unsigned long get_vsid(unsigned long context, unsigned long ea)
 164 {
 165         return vsid_scramble((context << USER_ESID_BITS)
 166                              | (ea >> SID_SHIFT));
 167 }
 168
 169 #endif /* __PPC64_MMU_CONTEXT_H */