1/*
2 * Copyright (C) 2009 Wind River Systems Inc
3 * Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
4 *
5 * based on arch/mips/mm/fault.c which is:
6 *
7 * Copyright (C) 1995-2000 Ralf Baechle
8 *
9 * This file is subject to the terms and conditions of the GNU General Public
10 * License. See the file "COPYING" in the main directory of this archive
11 * for more details.
12 */
13
14#include <linux/signal.h>
15#include <linux/sched.h>
16#include <linux/sched/debug.h>
17#include <linux/interrupt.h>
18#include <linux/kernel.h>
19#include <linux/errno.h>
20#include <linux/string.h>
21#include <linux/types.h>
22#include <linux/ptrace.h>
23#include <linux/mman.h>
24#include <linux/mm.h>
25#include <linux/extable.h>
26#include <linux/uaccess.h>
27#include <linux/perf_event.h>
28
29#include <asm/mmu_context.h>
30#include <asm/traps.h>
31
32#define EXC_SUPERV_INSN_ACCESS 9 /* Supervisor only instruction address */
33#define EXC_SUPERV_DATA_ACCESS 11 /* Supervisor only data address */
34#define EXC_X_PROTECTION_FAULT 13 /* TLB permission violation (x) */
35#define EXC_R_PROTECTION_FAULT 14 /* TLB permission violation (r) */
36#define EXC_W_PROTECTION_FAULT 15 /* TLB permission violation (w) */
37
38/*
39 * This routine handles page faults. It determines the address,
40 * and the problem, and then passes it off to one of the appropriate
41 * routines.
42 */
43asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
44 unsigned long address)
45{
46 struct vm_area_struct *vma = NULL;
47 struct task_struct *tsk = current;
48 struct mm_struct *mm = tsk->mm;
49 int code = SEGV_MAPERR;
50 vm_fault_t fault;
51 unsigned int flags = FAULT_FLAG_DEFAULT;
52
53 cause >>= 2;
54
55 /* Restart the instruction */
56 regs->ea -= 4;
57
58 /*
59 * We fault-in kernel-space virtual memory on-demand. The
60 * 'reference' page table is init_mm.pgd.
61 *
62 * NOTE! We MUST NOT take any locks for this case. We may
63 * be in an interrupt or a critical region, and should
64 * only copy the information from the master page table,
65 * nothing more.
66 */
67 if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END)) {
68 if (user_mode(regs))
69 goto bad_area_nosemaphore;
70 else
71 goto vmalloc_fault;
72 }
73
74 if (unlikely(address >= TASK_SIZE))
75 goto bad_area_nosemaphore;
76
77 /*
78 * If we're in an interrupt or have no user
79 * context, we must not take the fault..
80 */
81 if (faulthandler_disabled() || !mm)
82 goto bad_area_nosemaphore;
83
84 if (user_mode(regs))
85 flags |= FAULT_FLAG_USER;
86
87 perf_sw_event(event_id: PERF_COUNT_SW_PAGE_FAULTS, nr: 1, regs, addr: address);
88
89retry:
90 vma = lock_mm_and_find_vma(mm, address, regs);
91 if (!vma)
92 goto bad_area_nosemaphore;
93/*
94 * Ok, we have a good vm_area for this memory access, so
95 * we can handle it..
96 */
97 code = SEGV_ACCERR;
98
99 switch (cause) {
100 case EXC_SUPERV_INSN_ACCESS:
101 goto bad_area;
102 case EXC_SUPERV_DATA_ACCESS:
103 goto bad_area;
104 case EXC_X_PROTECTION_FAULT:
105 if (!(vma->vm_flags & VM_EXEC))
106 goto bad_area;
107 break;
108 case EXC_R_PROTECTION_FAULT:
109 if (!(vma->vm_flags & VM_READ))
110 goto bad_area;
111 break;
112 case EXC_W_PROTECTION_FAULT:
113 if (!(vma->vm_flags & VM_WRITE))
114 goto bad_area;
115 flags = FAULT_FLAG_WRITE;
116 break;
117 }
118
119 /*
120 * If for any reason at all we couldn't handle the fault,
121 * make sure we exit gracefully rather than endlessly redo
122 * the fault.
123 */
124 fault = handle_mm_fault(vma, address, flags, regs);
125
126 if (fault_signal_pending(fault_flags: fault, regs)) {
127 if (!user_mode(regs))
128 goto no_context;
129 return;
130 }
131
132 /* The fault is fully completed (including releasing mmap lock) */
133 if (fault & VM_FAULT_COMPLETED)
134 return;
135
136 if (unlikely(fault & VM_FAULT_ERROR)) {
137 if (fault & VM_FAULT_OOM)
138 goto out_of_memory;
139 else if (fault & VM_FAULT_SIGSEGV)
140 goto bad_area;
141 else if (fault & VM_FAULT_SIGBUS)
142 goto do_sigbus;
143 BUG();
144 }
145
146 if (fault & VM_FAULT_RETRY) {
147 flags |= FAULT_FLAG_TRIED;
148
149 /*
150 * No need to mmap_read_unlock(mm) as we would
151 * have already released it in __lock_page_or_retry
152 * in mm/filemap.c.
153 */
154
155 goto retry;
156 }
157
158 mmap_read_unlock(mm);
159 return;
160
161/*
162 * Something tried to access memory that isn't in our memory map..
163 * Fix it, but check if it's kernel or user first..
164 */
165bad_area:
166 mmap_read_unlock(mm);
167
168bad_area_nosemaphore:
169 /* User mode accesses just cause a SIGSEGV */
170 if (user_mode(regs)) {
171 if (unhandled_signal(current, SIGSEGV) && printk_ratelimit()) {
172 pr_info("%s: unhandled page fault (%d) at 0x%08lx, "
173 "cause %ld\n", current->comm, SIGSEGV, address, cause);
174 show_regs(regs);
175 }
176 _exception(SIGSEGV, regs, code, address);
177 return;
178 }
179
180no_context:
181 /* Are we prepared to handle this kernel fault? */
182 if (fixup_exception(regs))
183 return;
184
185 /*
186 * Oops. The kernel tried to access some bad page. We'll have to
187 * terminate things with extreme prejudice.
188 */
189 bust_spinlocks(yes: 1);
190
191 pr_alert("Unable to handle kernel %s at virtual address %08lx",
192 address < PAGE_SIZE ? "NULL pointer dereference" :
193 "paging request", address);
194 pr_alert("ea = %08lx, ra = %08lx, cause = %ld\n", regs->ea, regs->ra,
195 cause);
196 panic(fmt: "Oops");
197 return;
198
199/*
200 * We ran out of memory, or some other thing happened to us that made
201 * us unable to handle the page fault gracefully.
202 */
203out_of_memory:
204 mmap_read_unlock(mm);
205 if (!user_mode(regs))
206 goto no_context;
207 pagefault_out_of_memory();
208 return;
209
210do_sigbus:
211 mmap_read_unlock(mm);
212
213 /* Kernel mode? Handle exceptions or die */
214 if (!user_mode(regs))
215 goto no_context;
216
217 _exception(SIGBUS, regs, BUS_ADRERR, address);
218 return;
219
220vmalloc_fault:
221 {
222 /*
223 * Synchronize this task's top level page-table
224 * with the 'reference' page table.
225 *
226 * Do _not_ use "tsk" here. We might be inside
227 * an interrupt in the middle of a task switch..
228 */
229 int offset = pgd_index(address);
230 pgd_t *pgd, *pgd_k;
231 p4d_t *p4d, *p4d_k;
232 pud_t *pud, *pud_k;
233 pmd_t *pmd, *pmd_k;
234 pte_t *pte_k;
235
236 pgd = pgd_current + offset;
237 pgd_k = init_mm.pgd + offset;
238
239 if (!pgd_present(pgd: *pgd_k))
240 goto no_context;
241 set_pgd(pgd, *pgd_k);
242
243 p4d = p4d_offset(pgd, address);
244 p4d_k = p4d_offset(pgd: pgd_k, address);
245 if (!p4d_present(p4d: *p4d_k))
246 goto no_context;
247 pud = pud_offset(p4d, address);
248 pud_k = pud_offset(p4d: p4d_k, address);
249 if (!pud_present(pud: *pud_k))
250 goto no_context;
251 pmd = pmd_offset(pud, address);
252 pmd_k = pmd_offset(pud: pud_k, address);
253 if (!pmd_present(pmd: *pmd_k))
254 goto no_context;
255 set_pmd(pmdp: pmd, pmd: *pmd_k);
256
257 pte_k = pte_offset_kernel(pmd: pmd_k, address);
258 if (!pte_present(a: *pte_k))
259 goto no_context;
260
261 flush_tlb_kernel_page(address);
262 return;
263 }
264}
265

source code of linux/arch/nios2/mm/fault.c