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1 | /* | |
2 | * Copyright (C) 2014 Davidlohr Bueso. | |
3 | */ | |
4 | #include <linux/sched/signal.h> | |
5 | #include <linux/sched/task.h> | |
6 | #include <linux/mm.h> | |
7 | #include <linux/vmacache.h> | |
8 | ||
9 | /* | |
10 | * Flush vma caches for threads that share a given mm. | |
11 | * | |
12 | * The operation is safe because the caller holds the mmap_sem | |
13 | * exclusively and other threads accessing the vma cache will | |
14 | * have mmap_sem held at least for read, so no extra locking | |
15 | * is required to maintain the vma cache. | |
16 | */ | |
17 | void vmacache_flush_all(struct mm_struct *mm) | |
18 | { | |
19 | struct task_struct *g, *p; | |
20 | ||
21 | count_vm_vmacache_event(VMACACHE_FULL_FLUSHES); | |
22 | ||
23 | /* | |
24 | * Single threaded tasks need not iterate the entire | |
25 | * list of process. We can avoid the flushing as well | |
26 | * since the mm's seqnum was increased and don't have | |
27 | * to worry about other threads' seqnum. Current's | |
28 | * flush will occur upon the next lookup. | |
29 | */ | |
30 | if (atomic_read(&mm->mm_users) == 1) | |
31 | return; | |
32 | ||
33 | rcu_read_lock(); | |
34 | for_each_process_thread(g, p) { | |
35 | /* | |
36 | * Only flush the vmacache pointers as the | |
37 | * mm seqnum is already set and curr's will | |
38 | * be set upon invalidation when the next | |
39 | * lookup is done. | |
40 | */ | |
41 | if (mm == p->mm) | |
42 | vmacache_flush(p); | |
43 | } | |
44 | rcu_read_unlock(); | |
45 | } | |
46 | ||
47 | /* | |
48 | * This task may be accessing a foreign mm via (for example) | |
49 | * get_user_pages()->find_vma(). The vmacache is task-local and this | |
50 | * task's vmacache pertains to a different mm (ie, its own). There is | |
51 | * nothing we can do here. | |
52 | * | |
53 | * Also handle the case where a kernel thread has adopted this mm via use_mm(). | |
54 | * That kernel thread's vmacache is not applicable to this mm. | |
55 | */ | |
56 | static inline bool vmacache_valid_mm(struct mm_struct *mm) | |
57 | { | |
58 | return current->mm == mm && !(current->flags & PF_KTHREAD); | |
59 | } | |
60 | ||
61 | void vmacache_update(unsigned long addr, struct vm_area_struct *newvma) | |
62 | { | |
63 | if (vmacache_valid_mm(newvma->vm_mm)) | |
64 | current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma; | |
65 | } | |
66 | ||
67 | static bool vmacache_valid(struct mm_struct *mm) | |
68 | { | |
69 | struct task_struct *curr; | |
70 | ||
71 | if (!vmacache_valid_mm(mm)) | |
72 | return false; | |
73 | ||
74 | curr = current; | |
75 | if (mm->vmacache_seqnum != curr->vmacache.seqnum) { | |
76 | /* | |
77 | * First attempt will always be invalid, initialize | |
78 | * the new cache for this task here. | |
79 | */ | |
80 | curr->vmacache.seqnum = mm->vmacache_seqnum; | |
81 | vmacache_flush(curr); | |
82 | return false; | |
83 | } | |
84 | return true; | |
85 | } | |
86 | ||
87 | struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr) | |
88 | { | |
89 | int i; | |
90 | ||
91 | count_vm_vmacache_event(VMACACHE_FIND_CALLS); | |
92 | ||
93 | if (!vmacache_valid(mm)) | |
94 | return NULL; | |
95 | ||
96 | for (i = 0; i < VMACACHE_SIZE; i++) { | |
97 | struct vm_area_struct *vma = current->vmacache.vmas[i]; | |
98 | ||
99 | if (!vma) | |
100 | continue; | |
101 | if (WARN_ON_ONCE(vma->vm_mm != mm)) | |
102 | break; | |
103 | if (vma->vm_start <= addr && vma->vm_end > addr) { | |
104 | count_vm_vmacache_event(VMACACHE_FIND_HITS); | |
105 | return vma; | |
106 | } | |
107 | } | |
108 | ||
109 | return NULL; | |
110 | } | |
111 | ||
112 | #ifndef CONFIG_MMU | |
113 | struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm, | |
114 | unsigned long start, | |
115 | unsigned long end) | |
116 | { | |
117 | int i; | |
118 | ||
119 | count_vm_vmacache_event(VMACACHE_FIND_CALLS); | |
120 | ||
121 | if (!vmacache_valid(mm)) | |
122 | return NULL; | |
123 | ||
124 | for (i = 0; i < VMACACHE_SIZE; i++) { | |
125 | struct vm_area_struct *vma = current->vmacache.vmas[i]; | |
126 | ||
127 | if (vma && vma->vm_start == start && vma->vm_end == end) { | |
128 | count_vm_vmacache_event(VMACACHE_FIND_HITS); | |
129 | return vma; | |
130 | } | |
131 | } | |
132 | ||
133 | return NULL; | |
134 | } | |
135 | #endif |