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Linus Torvalds1da177e2005-04-16 15:20:36 -07001#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
52static 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
Kumar Gala33d9e9b2005-06-25 14:54:37 -070066#elif defined(CONFIG_E200) || defined(CONFIG_E500)
Linus Torvalds1da177e2005-04-16 15:20:36 -070067#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 */
89extern 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 */
95extern 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 */
102extern 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
111extern atomic_t nr_free_contexts;
112extern struct mm_struct *context_mm[LAST_CONTEXT+1];
113extern void steal_context(void);
114#endif
115
116/*
117 * Get a new mmu context for the address space described by `mm'.
118 */
119static 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 */
150static inline void destroy_context(struct mm_struct *mm)
151{
Guillaume Autranddca3b82005-07-13 01:10:45 -0700152 preempt_disable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153 if (mm->context != NO_CONTEXT) {
154 clear_bit(mm->context, context_map);
155 mm->context = NO_CONTEXT;
156#ifdef FEW_CONTEXTS
157 atomic_inc(&nr_free_contexts);
158#endif
159 }
Guillaume Autranddca3b82005-07-13 01:10:45 -0700160 preempt_enable();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161}
162
163static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
164 struct task_struct *tsk)
165{
166#ifdef CONFIG_ALTIVEC
167 asm volatile (
168 BEGIN_FTR_SECTION
169 "dssall;\n"
170#ifndef CONFIG_POWER4
171 "sync;\n" /* G4 needs a sync here, G5 apparently not */
172#endif
173 END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
174 : : );
175#endif /* CONFIG_ALTIVEC */
176
177 tsk->thread.pgdir = next->pgd;
178
179 /* No need to flush userspace segments if the mm doesnt change */
180 if (prev == next)
181 return;
182
183 /* Setup new userspace context */
184 get_mmu_context(next);
185 set_context(next->context, next->pgd);
186}
187
188#define deactivate_mm(tsk,mm) do { } while (0)
189
190/*
191 * After we have set current->mm to a new value, this activates
192 * the context for the new mm so we see the new mappings.
193 */
194#define activate_mm(active_mm, mm) switch_mm(active_mm, mm, current)
195
196extern void mmu_context_init(void);
197
198#endif /* __PPC_MMU_CONTEXT_H */
199#endif /* __KERNEL__ */