1/*
2 * OpenRISC fault.c
3 *
4 * Linux architectural port borrowing liberally from similar works of
5 * others.  All original copyrights apply as per the original source
6 * declaration.
7 *
8 * Modifications for the OpenRISC architecture:
9 * Copyright (C) 2003 Matjaz Breskvar <phoenix@bsemi.com>
10 * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
11 *
12 *      This program is free software; you can redistribute it and/or
13 *      modify it under the terms of the GNU General Public License
14 *      as published by the Free Software Foundation; either version
15 *      2 of the License, or (at your option) any later version.
16 */
17
18#include <linux/mm.h>
19#include <linux/interrupt.h>
20#include <linux/module.h>
21#include <linux/sched.h>
22
23#include <asm/uaccess.h>
24#include <asm/siginfo.h>
25#include <asm/signal.h>
26
27#define NUM_TLB_ENTRIES 64
28#define TLB_OFFSET(add) (((add) >> PAGE_SHIFT) & (NUM_TLB_ENTRIES-1))
29
30unsigned long pte_misses;	/* updated by do_page_fault() */
31unsigned long pte_errors;	/* updated by do_page_fault() */
32
33/* __PHX__ :: - check the vmalloc_fault in do_page_fault()
34 *            - also look into include/asm-or32/mmu_context.h
35 */
36volatile pgd_t *current_pgd;
37
38extern void die(char *, struct pt_regs *, long);
39
40/*
41 * This routine handles page faults.  It determines the address,
42 * and the problem, and then passes it off to one of the appropriate
43 * routines.
44 *
45 * If this routine detects a bad access, it returns 1, otherwise it
46 * returns 0.
47 */
48
49asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
50			      unsigned long vector, int write_acc)
51{
52	struct task_struct *tsk;
53	struct mm_struct *mm;
54	struct vm_area_struct *vma;
55	siginfo_t info;
56	int fault;
57	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
58
59	tsk = current;
60
61	/*
62	 * We fault-in kernel-space virtual memory on-demand. The
63	 * 'reference' page table is init_mm.pgd.
64	 *
65	 * NOTE! We MUST NOT take any locks for this case. We may
66	 * be in an interrupt or a critical region, and should
67	 * only copy the information from the master page table,
68	 * nothing more.
69	 *
70	 * NOTE2: This is done so that, when updating the vmalloc
71	 * mappings we don't have to walk all processes pgdirs and
72	 * add the high mappings all at once. Instead we do it as they
73	 * are used. However vmalloc'ed page entries have the PAGE_GLOBAL
74	 * bit set so sometimes the TLB can use a lingering entry.
75	 *
76	 * This verifies that the fault happens in kernel space
77	 * and that the fault was not a protection error.
78	 */
79
80	if (address >= VMALLOC_START &&
81	    (vector != 0x300 && vector != 0x400) &&
82	    !user_mode(regs))
83		goto vmalloc_fault;
84
85	/* If exceptions were enabled, we can reenable them here */
86	if (user_mode(regs)) {
87		/* Exception was in userspace: reenable interrupts */
88		local_irq_enable();
89		flags |= FAULT_FLAG_USER;
90	} else {
91		/* If exception was in a syscall, then IRQ's may have
92		 * been enabled or disabled.  If they were enabled,
93		 * reenable them.
94		 */
95		if (regs->sr && (SPR_SR_IEE | SPR_SR_TEE))
96			local_irq_enable();
97	}
98
99	mm = tsk->mm;
100	info.si_code = SEGV_MAPERR;
101
102	/*
103	 * If we're in an interrupt or have no user
104	 * context, we must not take the fault..
105	 */
106
107	if (in_interrupt() || !mm)
108		goto no_context;
109
110retry:
111	down_read(&mm->mmap_sem);
112	vma = find_vma(mm, address);
113
114	if (!vma)
115		goto bad_area;
116
117	if (vma->vm_start <= address)
118		goto good_area;
119
120	if (!(vma->vm_flags & VM_GROWSDOWN))
121		goto bad_area;
122
123	if (user_mode(regs)) {
124		/*
125		 * accessing the stack below usp is always a bug.
126		 * we get page-aligned addresses so we can only check
127		 * if we're within a page from usp, but that might be
128		 * enough to catch brutal errors at least.
129		 */
130		if (address + PAGE_SIZE < regs->sp)
131			goto bad_area;
132	}
133	if (expand_stack(vma, address))
134		goto bad_area;
135
136	/*
137	 * Ok, we have a good vm_area for this memory access, so
138	 * we can handle it..
139	 */
140
141good_area:
142	info.si_code = SEGV_ACCERR;
143
144	/* first do some preliminary protection checks */
145
146	if (write_acc) {
147		if (!(vma->vm_flags & VM_WRITE))
148			goto bad_area;
149		flags |= FAULT_FLAG_WRITE;
150	} else {
151		/* not present */
152		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
153			goto bad_area;
154	}
155
156	/* are we trying to execute nonexecutable area */
157	if ((vector == 0x400) && !(vma->vm_page_prot.pgprot & _PAGE_EXEC))
158		goto bad_area;
159
160	/*
161	 * If for any reason at all we couldn't handle the fault,
162	 * make sure we exit gracefully rather than endlessly redo
163	 * the fault.
164	 */
165
166	fault = handle_mm_fault(mm, vma, address, flags);
167
168	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
169		return;
170
171	if (unlikely(fault & VM_FAULT_ERROR)) {
172		if (fault & VM_FAULT_OOM)
173			goto out_of_memory;
174		else if (fault & VM_FAULT_SIGSEGV)
175			goto bad_area;
176		else if (fault & VM_FAULT_SIGBUS)
177			goto do_sigbus;
178		BUG();
179	}
180
181	if (flags & FAULT_FLAG_ALLOW_RETRY) {
182		/*RGD modeled on Cris */
183		if (fault & VM_FAULT_MAJOR)
184			tsk->maj_flt++;
185		else
186			tsk->min_flt++;
187		if (fault & VM_FAULT_RETRY) {
188			flags &= ~FAULT_FLAG_ALLOW_RETRY;
189			flags |= FAULT_FLAG_TRIED;
190
191			 /* No need to up_read(&mm->mmap_sem) as we would
192			 * have already released it in __lock_page_or_retry
193			 * in mm/filemap.c.
194			 */
195
196			goto retry;
197		}
198	}
199
200	up_read(&mm->mmap_sem);
201	return;
202
203	/*
204	 * Something tried to access memory that isn't in our memory map..
205	 * Fix it, but check if it's kernel or user first..
206	 */
207
208bad_area:
209	up_read(&mm->mmap_sem);
210
211bad_area_nosemaphore:
212
213	/* User mode accesses just cause a SIGSEGV */
214
215	if (user_mode(regs)) {
216		info.si_signo = SIGSEGV;
217		info.si_errno = 0;
218		/* info.si_code has been set above */
219		info.si_addr = (void *)address;
220		force_sig_info(SIGSEGV, &info, tsk);
221		return;
222	}
223
224no_context:
225
226	/* Are we prepared to handle this kernel fault?
227	 *
228	 * (The kernel has valid exception-points in the source
229	 *  when it acesses user-memory. When it fails in one
230	 *  of those points, we find it in a table and do a jump
231	 *  to some fixup code that loads an appropriate error
232	 *  code)
233	 */
234
235	{
236		const struct exception_table_entry *entry;
237
238		__asm__ __volatile__("l.nop 42");
239
240		if ((entry = search_exception_tables(regs->pc)) != NULL) {
241			/* Adjust the instruction pointer in the stackframe */
242			regs->pc = entry->fixup;
243			return;
244		}
245	}
246
247	/*
248	 * Oops. The kernel tried to access some bad page. We'll have to
249	 * terminate things with extreme prejudice.
250	 */
251
252	if ((unsigned long)(address) < PAGE_SIZE)
253		printk(KERN_ALERT
254		       "Unable to handle kernel NULL pointer dereference");
255	else
256		printk(KERN_ALERT "Unable to handle kernel access");
257	printk(" at virtual address 0x%08lx\n", address);
258
259	die("Oops", regs, write_acc);
260
261	do_exit(SIGKILL);
262
263	/*
264	 * We ran out of memory, or some other thing happened to us that made
265	 * us unable to handle the page fault gracefully.
266	 */
267
268out_of_memory:
269	__asm__ __volatile__("l.nop 42");
270	__asm__ __volatile__("l.nop 1");
271
272	up_read(&mm->mmap_sem);
273	if (!user_mode(regs))
274		goto no_context;
275	pagefault_out_of_memory();
276	return;
277
278do_sigbus:
279	up_read(&mm->mmap_sem);
280
281	/*
282	 * Send a sigbus, regardless of whether we were in kernel
283	 * or user mode.
284	 */
285	info.si_signo = SIGBUS;
286	info.si_errno = 0;
287	info.si_code = BUS_ADRERR;
288	info.si_addr = (void *)address;
289	force_sig_info(SIGBUS, &info, tsk);
290
291	/* Kernel mode? Handle exceptions or die */
292	if (!user_mode(regs))
293		goto no_context;
294	return;
295
296vmalloc_fault:
297	{
298		/*
299		 * Synchronize this task's top level page-table
300		 * with the 'reference' page table.
301		 *
302		 * Use current_pgd instead of tsk->active_mm->pgd
303		 * since the latter might be unavailable if this
304		 * code is executed in a misfortunately run irq
305		 * (like inside schedule() between switch_mm and
306		 *  switch_to...).
307		 */
308
309		int offset = pgd_index(address);
310		pgd_t *pgd, *pgd_k;
311		pud_t *pud, *pud_k;
312		pmd_t *pmd, *pmd_k;
313		pte_t *pte_k;
314
315/*
316		phx_warn("do_page_fault(): vmalloc_fault will not work, "
317			 "since current_pgd assign a proper value somewhere\n"
318			 "anyhow we don't need this at the moment\n");
319
320		phx_mmu("vmalloc_fault");
321*/
322		pgd = (pgd_t *)current_pgd + offset;
323		pgd_k = init_mm.pgd + offset;
324
325		/* Since we're two-level, we don't need to do both
326		 * set_pgd and set_pmd (they do the same thing). If
327		 * we go three-level at some point, do the right thing
328		 * with pgd_present and set_pgd here.
329		 *
330		 * Also, since the vmalloc area is global, we don't
331		 * need to copy individual PTE's, it is enough to
332		 * copy the pgd pointer into the pte page of the
333		 * root task. If that is there, we'll find our pte if
334		 * it exists.
335		 */
336
337		pud = pud_offset(pgd, address);
338		pud_k = pud_offset(pgd_k, address);
339		if (!pud_present(*pud_k))
340			goto no_context;
341
342		pmd = pmd_offset(pud, address);
343		pmd_k = pmd_offset(pud_k, address);
344
345		if (!pmd_present(*pmd_k))
346			goto bad_area_nosemaphore;
347
348		set_pmd(pmd, *pmd_k);
349
350		/* Make sure the actual PTE exists as well to
351		 * catch kernel vmalloc-area accesses to non-mapped
352		 * addresses. If we don't do this, this will just
353		 * silently loop forever.
354		 */
355
356		pte_k = pte_offset_kernel(pmd_k, address);
357		if (!pte_present(*pte_k))
358			goto no_context;
359
360		return;
361	}
362}
363