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mmu_context.h
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1 /*
2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License
6  * as published by the Free Software Foundation, version 2.
7  *
8  * This program is distributed in the hope that it will be useful, but
9  * WITHOUT ANY WARRANTY; without even the implied warranty of
10  * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11  * NON INFRINGEMENT. See the GNU General Public License for
12  * more details.
13  */
14 
15 #ifndef _ASM_TILE_MMU_CONTEXT_H
16 #define _ASM_TILE_MMU_CONTEXT_H
17 
18 #include <linux/smp.h>
19 #include <asm/setup.h>
20 #include <asm/page.h>
21 #include <asm/pgalloc.h>
22 #include <asm/pgtable.h>
23 #include <asm/tlbflush.h>
24 #include <asm/homecache.h>
25 #include <asm-generic/mm_hooks.h>
26 
27 static inline int
28 init_new_context(struct task_struct *tsk, struct mm_struct *mm)
29 {
30  return 0;
31 }
32 
33 /*
34  * Note that arch/tile/kernel/head_NN.S and arch/tile/mm/migrate_NN.S
35  * also call hv_install_context().
36  */
37 static inline void __install_page_table(pgd_t *pgdir, int asid, pgprot_t prot)
38 {
39  /* FIXME: DIRECTIO should not always be set. FIXME. */
40  int rc = hv_install_context(__pa(pgdir), prot, asid,
42  if (rc < 0)
43  panic("hv_install_context failed: %d", rc);
44 }
45 
46 static inline void install_page_table(pgd_t *pgdir, int asid)
47 {
48  pte_t *ptep = virt_to_pte(NULL, (unsigned long)pgdir);
49  __install_page_table(pgdir, asid, *ptep);
50 }
51 
52 /*
53  * "Lazy" TLB mode is entered when we are switching to a kernel task,
54  * which borrows the mm of the previous task. The goal of this
55  * optimization is to avoid having to install a new page table. On
56  * early x86 machines (where the concept originated) you couldn't do
57  * anything short of a full page table install for invalidation, so
58  * handling a remote TLB invalidate required doing a page table
59  * re-install. Someone clearly decided that it was silly to keep
60  * doing this while in "lazy" TLB mode, so the optimization involves
61  * installing the swapper page table instead the first time one
62  * occurs, and clearing the cpu out of cpu_vm_mask, so the cpu running
63  * the kernel task doesn't need to take any more interrupts. At that
64  * point it's then necessary to explicitly reinstall it when context
65  * switching back to the original mm.
66  *
67  * On Tile, we have to do a page-table install whenever DMA is enabled,
68  * so in that case lazy mode doesn't help anyway. And more generally,
69  * we have efficient per-page TLB shootdown, and don't expect to spend
70  * that much time in kernel tasks in general, so just leaving the
71  * kernel task borrowing the old page table, but handling TLB
72  * shootdowns, is a reasonable thing to do. And importantly, this
73  * lets us use the hypervisor's internal APIs for TLB shootdown, which
74  * means we don't have to worry about having TLB shootdowns blocked
75  * when Linux is disabling interrupts; see the page migration code for
76  * an example of where it's important for TLB shootdowns to complete
77  * even when interrupts are disabled at the Linux level.
78  */
79 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *t)
80 {
81 #if CHIP_HAS_TILE_DMA()
82  /*
83  * We have to do an "identity" page table switch in order to
84  * clear any pending DMA interrupts.
85  */
86  if (current->thread.tile_dma_state.enabled)
87  install_page_table(mm->pgd, __get_cpu_var(current_asid));
88 #endif
89 }
90 
91 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
92  struct task_struct *tsk)
93 {
94  if (likely(prev != next)) {
95 
96  int cpu = smp_processor_id();
97 
98  /* Pick new ASID. */
99  int asid = __get_cpu_var(current_asid) + 1;
100  if (asid > max_asid) {
101  asid = min_asid;
102  local_flush_tlb();
103  }
104  __get_cpu_var(current_asid) = asid;
105 
106  /* Clear cpu from the old mm, and set it in the new one. */
107  cpumask_clear_cpu(cpu, mm_cpumask(prev));
108  cpumask_set_cpu(cpu, mm_cpumask(next));
109 
110  /* Re-load page tables */
111  install_page_table(next->pgd, asid);
112 
113  /* See how we should set the red/black cache info */
114  check_mm_caching(prev, next);
115 
116  /*
117  * Since we're changing to a new mm, we have to flush
118  * the icache in case some physical page now being mapped
119  * has subsequently been repurposed and has new code.
120  */
121  __flush_icache();
122 
123  }
124 }
125 
126 static inline void activate_mm(struct mm_struct *prev_mm,
127  struct mm_struct *next_mm)
128 {
129  switch_mm(prev_mm, next_mm, NULL);
130 }
131 
132 #define destroy_context(mm) do { } while (0)
133 #define deactivate_mm(tsk, mm) do { } while (0)
134 
135 #endif /* _ASM_TILE_MMU_CONTEXT_H */