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