ea517bef7dc552a10ac6ed424ca06aa50670c303
[muen/linux.git] / mm / vmacache.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2014 Davidlohr Bueso.
4  */
5 #include <linux/sched/signal.h>
6 #include <linux/sched/task.h>
7 #include <linux/mm.h>
8 #include <linux/vmacache.h>
9 #include <asm/pgtable.h>
10
11 /*
12  * Hash based on the pmd of addr if configured with MMU, which provides a good
13  * hit rate for workloads with spatial locality.  Otherwise, use pages.
14  */
15 #ifdef CONFIG_MMU
16 #define VMACACHE_SHIFT  PMD_SHIFT
17 #else
18 #define VMACACHE_SHIFT  PAGE_SHIFT
19 #endif
20 #define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
21
22 /*
23  * Flush vma caches for threads that share a given mm.
24  *
25  * The operation is safe because the caller holds the mmap_sem
26  * exclusively and other threads accessing the vma cache will
27  * have mmap_sem held at least for read, so no extra locking
28  * is required to maintain the vma cache.
29  */
30 void vmacache_flush_all(struct mm_struct *mm)
31 {
32         struct task_struct *g, *p;
33
34         count_vm_vmacache_event(VMACACHE_FULL_FLUSHES);
35
36         /*
37          * Single threaded tasks need not iterate the entire
38          * list of process. We can avoid the flushing as well
39          * since the mm's seqnum was increased and don't have
40          * to worry about other threads' seqnum. Current's
41          * flush will occur upon the next lookup.
42          */
43         if (atomic_read(&mm->mm_users) == 1)
44                 return;
45
46         rcu_read_lock();
47         for_each_process_thread(g, p) {
48                 /*
49                  * Only flush the vmacache pointers as the
50                  * mm seqnum is already set and curr's will
51                  * be set upon invalidation when the next
52                  * lookup is done.
53                  */
54                 if (mm == p->mm)
55                         vmacache_flush(p);
56         }
57         rcu_read_unlock();
58 }
59
60 /*
61  * This task may be accessing a foreign mm via (for example)
62  * get_user_pages()->find_vma().  The vmacache is task-local and this
63  * task's vmacache pertains to a different mm (ie, its own).  There is
64  * nothing we can do here.
65  *
66  * Also handle the case where a kernel thread has adopted this mm via use_mm().
67  * That kernel thread's vmacache is not applicable to this mm.
68  */
69 static inline bool vmacache_valid_mm(struct mm_struct *mm)
70 {
71         return current->mm == mm && !(current->flags & PF_KTHREAD);
72 }
73
74 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
75 {
76         if (vmacache_valid_mm(newvma->vm_mm))
77                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
78 }
79
80 static bool vmacache_valid(struct mm_struct *mm)
81 {
82         struct task_struct *curr;
83
84         if (!vmacache_valid_mm(mm))
85                 return false;
86
87         curr = current;
88         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
89                 /*
90                  * First attempt will always be invalid, initialize
91                  * the new cache for this task here.
92                  */
93                 curr->vmacache.seqnum = mm->vmacache_seqnum;
94                 vmacache_flush(curr);
95                 return false;
96         }
97         return true;
98 }
99
100 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
101 {
102         int idx = VMACACHE_HASH(addr);
103         int i;
104
105         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
106
107         if (!vmacache_valid(mm))
108                 return NULL;
109
110         for (i = 0; i < VMACACHE_SIZE; i++) {
111                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
112
113                 if (vma) {
114 #ifdef CONFIG_DEBUG_VM_VMACACHE
115                         if (WARN_ON_ONCE(vma->vm_mm != mm))
116                                 break;
117 #endif
118                         if (vma->vm_start <= addr && vma->vm_end > addr) {
119                                 count_vm_vmacache_event(VMACACHE_FIND_HITS);
120                                 return vma;
121                         }
122                 }
123                 if (++idx == VMACACHE_SIZE)
124                         idx = 0;
125         }
126
127         return NULL;
128 }
129
130 #ifndef CONFIG_MMU
131 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
132                                            unsigned long start,
133                                            unsigned long end)
134 {
135         int idx = VMACACHE_HASH(start);
136         int i;
137
138         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
139
140         if (!vmacache_valid(mm))
141                 return NULL;
142
143         for (i = 0; i < VMACACHE_SIZE; i++) {
144                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
145
146                 if (vma && vma->vm_start == start && vma->vm_end == end) {
147                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
148                         return vma;
149                 }
150                 if (++idx == VMACACHE_SIZE)
151                         idx = 0;
152         }
153
154         return NULL;
155 }
156 #endif