1/* Page Fault Handling for ARC (TLB Miss / ProtV)
2 *
3 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 */
9
10#include <linux/signal.h>
11#include <linux/interrupt.h>
12#include <linux/sched.h>
13#include <linux/errno.h>
14#include <linux/ptrace.h>
15#include <linux/uaccess.h>
16#include <linux/kdebug.h>
17#include <linux/perf_event.h>
18#include <asm/pgalloc.h>
19#include <asm/mmu.h>
20
21/*
22 * kernel virtual address is required to implement vmalloc/pkmap/fixmap
23 * Refer to asm/processor.h for System Memory Map
24 *
25 * It simply copies the PMD entry (pointer to 2nd level page table or hugepage)
26 * from swapper pgdir to task pgdir. The 2nd level table/page is thus shared
27 */
28noinline static int handle_kernel_vaddr_fault(unsigned long address)
29{
30	/*
31	 * Synchronize this task's top level page-table
32	 * with the 'reference' page table.
33	 */
34	pgd_t *pgd, *pgd_k;
35	pud_t *pud, *pud_k;
36	pmd_t *pmd, *pmd_k;
37
38	pgd = pgd_offset_fast(current->active_mm, address);
39	pgd_k = pgd_offset_k(address);
40
41	if (!pgd_present(*pgd_k))
42		goto bad_area;
43
44	pud = pud_offset(pgd, address);
45	pud_k = pud_offset(pgd_k, address);
46	if (!pud_present(*pud_k))
47		goto bad_area;
48
49	pmd = pmd_offset(pud, address);
50	pmd_k = pmd_offset(pud_k, address);
51	if (!pmd_present(*pmd_k))
52		goto bad_area;
53
54	set_pmd(pmd, *pmd_k);
55
56	/* XXX: create the TLB entry here */
57	return 0;
58
59bad_area:
60	return 1;
61}
62
63void do_page_fault(unsigned long address, struct pt_regs *regs)
64{
65	struct vm_area_struct *vma = NULL;
66	struct task_struct *tsk = current;
67	struct mm_struct *mm = tsk->mm;
68	siginfo_t info;
69	int fault, ret;
70	int write = regs->ecr_cause & ECR_C_PROTV_STORE;  /* ST/EX */
71	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
72
73	/*
74	 * We fault-in kernel-space virtual memory on-demand. The
75	 * 'reference' page table is init_mm.pgd.
76	 *
77	 * NOTE! We MUST NOT take any locks for this case. We may
78	 * be in an interrupt or a critical region, and should
79	 * only copy the information from the master page table,
80	 * nothing more.
81	 */
82	if (address >= VMALLOC_START) {
83		ret = handle_kernel_vaddr_fault(address);
84		if (unlikely(ret))
85			goto bad_area_nosemaphore;
86		else
87			return;
88	}
89
90	info.si_code = SEGV_MAPERR;
91
92	/*
93	 * If we're in an interrupt or have no user
94	 * context, we must not take the fault..
95	 */
96	if (faulthandler_disabled() || !mm)
97		goto no_context;
98
99	if (user_mode(regs))
100		flags |= FAULT_FLAG_USER;
101retry:
102	down_read(&mm->mmap_sem);
103	vma = find_vma(mm, address);
104	if (!vma)
105		goto bad_area;
106	if (vma->vm_start <= address)
107		goto good_area;
108	if (!(vma->vm_flags & VM_GROWSDOWN))
109		goto bad_area;
110	if (expand_stack(vma, address))
111		goto bad_area;
112
113	/*
114	 * Ok, we have a good vm_area for this memory access, so
115	 * we can handle it..
116	 */
117good_area:
118	info.si_code = SEGV_ACCERR;
119
120	/* Handle protection violation, execute on heap or stack */
121
122	if ((regs->ecr_vec == ECR_V_PROTV) &&
123	    (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
124		goto bad_area;
125
126	if (write) {
127		if (!(vma->vm_flags & VM_WRITE))
128			goto bad_area;
129		flags |= FAULT_FLAG_WRITE;
130	} else {
131		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
132			goto bad_area;
133	}
134
135	/*
136	 * If for any reason at all we couldn't handle the fault,
137	 * make sure we exit gracefully rather than endlessly redo
138	 * the fault.
139	 */
140	fault = handle_mm_fault(mm, vma, address, flags);
141
142	/* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
143	if (unlikely(fatal_signal_pending(current))) {
144		if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
145			up_read(&mm->mmap_sem);
146		if (user_mode(regs))
147			return;
148	}
149
150	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
151
152	if (likely(!(fault & VM_FAULT_ERROR))) {
153		if (flags & FAULT_FLAG_ALLOW_RETRY) {
154			/* To avoid updating stats twice for retry case */
155			if (fault & VM_FAULT_MAJOR) {
156				tsk->maj_flt++;
157				perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
158					      regs, address);
159			} else {
160				tsk->min_flt++;
161				perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
162					      regs, address);
163			}
164
165			if (fault & VM_FAULT_RETRY) {
166				flags &= ~FAULT_FLAG_ALLOW_RETRY;
167				flags |= FAULT_FLAG_TRIED;
168				goto retry;
169			}
170		}
171
172		/* Fault Handled Gracefully */
173		up_read(&mm->mmap_sem);
174		return;
175	}
176
177	if (fault & VM_FAULT_OOM)
178		goto out_of_memory;
179	else if (fault & VM_FAULT_SIGSEGV)
180		goto bad_area;
181	else if (fault & VM_FAULT_SIGBUS)
182		goto do_sigbus;
183
184	/* no man's land */
185	BUG();
186
187	/*
188	 * Something tried to access memory that isn't in our memory map..
189	 * Fix it, but check if it's kernel or user first..
190	 */
191bad_area:
192	up_read(&mm->mmap_sem);
193
194bad_area_nosemaphore:
195	/* User mode accesses just cause a SIGSEGV */
196	if (user_mode(regs)) {
197		tsk->thread.fault_address = address;
198		info.si_signo = SIGSEGV;
199		info.si_errno = 0;
200		/* info.si_code has been set above */
201		info.si_addr = (void __user *)address;
202		force_sig_info(SIGSEGV, &info, tsk);
203		return;
204	}
205
206no_context:
207	/* Are we prepared to handle this kernel fault?
208	 *
209	 * (The kernel has valid exception-points in the source
210	 *  when it acesses user-memory. When it fails in one
211	 *  of those points, we find it in a table and do a jump
212	 *  to some fixup code that loads an appropriate error
213	 *  code)
214	 */
215	if (fixup_exception(regs))
216		return;
217
218	die("Oops", regs, address);
219
220out_of_memory:
221	up_read(&mm->mmap_sem);
222
223	if (user_mode(regs)) {
224		pagefault_out_of_memory();
225		return;
226	}
227
228	goto no_context;
229
230do_sigbus:
231	up_read(&mm->mmap_sem);
232
233	if (!user_mode(regs))
234		goto no_context;
235
236	tsk->thread.fault_address = address;
237	info.si_signo = SIGBUS;
238	info.si_errno = 0;
239	info.si_code = BUS_ADRERR;
240	info.si_addr = (void __user *)address;
241	force_sig_info(SIGBUS, &info, tsk);
242}
243