1/*
  2 * Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
  3 *  Lennox Wu <lennox.wu@sunplusct.com>
  4 *  Chen Liqin <liqin.chen@sunplusct.com>
  5 * Copyright (C) 2012 Regents of the University of California
  6 *
  7 * This program is free software; you can redistribute it and/or modify
  8 * it under the terms of the GNU General Public License as published by
  9 * the Free Software Foundation; either version 2 of the License, or
 10 * (at your option) any later version.
 11 *
 12 * This program is distributed in the hope that it will be useful,
 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15 * GNU General Public License for more details.
 16 *
 17 * You should have received a copy of the GNU General Public License
 18 * along with this program; if not, see the file COPYING, or write
 19 * to the Free Software Foundation, Inc.,
 20 */
 21
 22
 23#include <linux/mm.h>
 24#include <linux/kernel.h>
 25#include <linux/interrupt.h>
 26#include <linux/perf_event.h>
 27#include <linux/signal.h>
 28#include <linux/uaccess.h>
 29
 30#include <asm/pgalloc.h>
 31#include <asm/ptrace.h>
 32
 33/*
 34 * This routine handles page faults.  It determines the address and the
 35 * problem, and then passes it off to one of the appropriate routines.
 36 */
 37asmlinkage void do_page_fault(struct pt_regs *regs)
 38{
 39	struct task_struct *tsk;
 40	struct vm_area_struct *vma;
 41	struct mm_struct *mm;
 42	unsigned long addr, cause;
 43	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 44	int fault, code = SEGV_MAPERR;
 45
 46	cause = regs->scause;
 47	addr = regs->sbadaddr;
 48
 49	tsk = current;
 50	mm = tsk->mm;
 51
 52	/*
 53	 * Fault-in kernel-space virtual memory on-demand.
 54	 * The 'reference' page table is init_mm.pgd.
 55	 *
 56	 * NOTE! We MUST NOT take any locks for this case. We may
 57	 * be in an interrupt or a critical region, and should
 58	 * only copy the information from the master page table,
 59	 * nothing more.
 60	 */
 61	if (unlikely((addr >= VMALLOC_START) && (addr <= VMALLOC_END)))
 62		goto vmalloc_fault;
 63
 64	/* Enable interrupts if they were enabled in the parent context. */
 65	if (likely(regs->sstatus & SR_SPIE))
 66		local_irq_enable();
 67
 68	/*
 69	 * If we're in an interrupt, have no user context, or are running
 70	 * in an atomic region, then we must not take the fault.
 71	 */
 72	if (unlikely(faulthandler_disabled() || !mm))
 73		goto no_context;
 74
 75	if (user_mode(regs))
 76		flags |= FAULT_FLAG_USER;
 77
 78	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 79
 80retry:
 81	down_read(&mm->mmap_sem);
 82	vma = find_vma(mm, addr);
 83	if (unlikely(!vma))
 84		goto bad_area;
 85	if (likely(vma->vm_start <= addr))
 86		goto good_area;
 87	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
 88		goto bad_area;
 89	if (unlikely(expand_stack(vma, addr)))
 90		goto bad_area;
 91
 92	/*
 93	 * Ok, we have a good vm_area for this memory access, so
 94	 * we can handle it.
 95	 */
 96good_area:
 97	code = SEGV_ACCERR;
 98
 99	switch (cause) {
100	case EXC_INST_PAGE_FAULT:
101		if (!(vma->vm_flags & VM_EXEC))
102			goto bad_area;
103		break;
104	case EXC_LOAD_PAGE_FAULT:
105		if (!(vma->vm_flags & VM_READ))
106			goto bad_area;
107		break;
108	case EXC_STORE_PAGE_FAULT:
109		if (!(vma->vm_flags & VM_WRITE))
110			goto bad_area;
111		flags |= FAULT_FLAG_WRITE;
112		break;
113	default:
114		panic("%s: unhandled cause %lu", __func__, cause);
115	}
116
117	/*
118	 * If for any reason at all we could not handle the fault,
119	 * make sure we exit gracefully rather than endlessly redo
120	 * the fault.
121	 */
122	fault = handle_mm_fault(vma, addr, flags);
123
124	/*
125	 * If we need to retry but a fatal signal is pending, handle the
126	 * signal first. We do not need to release the mmap_sem because it
127	 * would already be released in __lock_page_or_retry in mm/filemap.c.
128	 */
129	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
130		return;
131
132	if (unlikely(fault & VM_FAULT_ERROR)) {
133		if (fault & VM_FAULT_OOM)
134			goto out_of_memory;
135		else if (fault & VM_FAULT_SIGBUS)
136			goto do_sigbus;
137		BUG();
138	}
139
140	/*
141	 * Major/minor page fault accounting is only done on the
142	 * initial attempt. If we go through a retry, it is extremely
143	 * likely that the page will be found in page cache at that point.
144	 */
145	if (flags & FAULT_FLAG_ALLOW_RETRY) {
146		if (fault & VM_FAULT_MAJOR) {
147			tsk->maj_flt++;
148			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ,
149				      1, regs, addr);
150		} else {
151			tsk->min_flt++;
152			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
153				      1, regs, addr);
154		}
155		if (fault & VM_FAULT_RETRY) {
156			/*
157			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
158			 * of starvation.
159			 */
160			flags &= ~(FAULT_FLAG_ALLOW_RETRY);
161			flags |= FAULT_FLAG_TRIED;
162
163			/*
164			 * No need to up_read(&mm->mmap_sem) as we would
165			 * have already released it in __lock_page_or_retry
166			 * in mm/filemap.c.
167			 */
168			goto retry;
169		}
170	}
171
172	up_read(&mm->mmap_sem);
173	return;
174
175	/*
176	 * Something tried to access memory that isn't in our memory map.
177	 * Fix it, but check if it's kernel or user first.
178	 */
179bad_area:
180	up_read(&mm->mmap_sem);
181	/* User mode accesses just cause a SIGSEGV */
182	if (user_mode(regs)) {
183		do_trap(regs, SIGSEGV, code, addr, tsk);
184		return;
185	}
186
187no_context:
188	/* Are we prepared to handle this kernel fault? */
189	if (fixup_exception(regs))
190		return;
191
192	/*
193	 * Oops. The kernel tried to access some bad page. We'll have to
194	 * terminate things with extreme prejudice.
195	 */
196	bust_spinlocks(1);
197	pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n",
198		(addr < PAGE_SIZE) ? "NULL pointer dereference" :
199		"paging request", addr);
200	die(regs, "Oops");
201	do_exit(SIGKILL);
202
203	/*
204	 * We ran out of memory, call the OOM killer, and return the userspace
205	 * (which will retry the fault, or kill us if we got oom-killed).
206	 */
207out_of_memory:
208	up_read(&mm->mmap_sem);
209	if (!user_mode(regs))
210		goto no_context;
211	pagefault_out_of_memory();
212	return;
213
214do_sigbus:
215	up_read(&mm->mmap_sem);
216	/* Kernel mode? Handle exceptions or die */
217	if (!user_mode(regs))
218		goto no_context;
219	do_trap(regs, SIGBUS, BUS_ADRERR, addr, tsk);
220	return;
221
222vmalloc_fault:
223	{
224		pgd_t *pgd, *pgd_k;
225		pud_t *pud, *pud_k;
226		p4d_t *p4d, *p4d_k;
227		pmd_t *pmd, *pmd_k;
228		pte_t *pte_k;
229		int index;
230
231		if (user_mode(regs))
232			goto bad_area;
233
234		/*
235		 * Synchronize this task's top level page-table
236		 * with the 'reference' page table.
237		 *
238		 * Do _not_ use "tsk->active_mm->pgd" here.
239		 * We might be inside an interrupt in the middle
240		 * of a task switch.
241		 *
242		 * Note: Use the old spbtr name instead of using the current
243		 * satp name to support binutils 2.29 which doesn't know about
244		 * the privileged ISA 1.10 yet.
245		 */
246		index = pgd_index(addr);
247		pgd = (pgd_t *)pfn_to_virt(csr_read(sptbr)) + index;
248		pgd_k = init_mm.pgd + index;
249
250		if (!pgd_present(*pgd_k))
251			goto no_context;
252		set_pgd(pgd, *pgd_k);
253
254		p4d = p4d_offset(pgd, addr);
255		p4d_k = p4d_offset(pgd_k, addr);
256		if (!p4d_present(*p4d_k))
257			goto no_context;
258
259		pud = pud_offset(p4d, addr);
260		pud_k = pud_offset(p4d_k, addr);
261		if (!pud_present(*pud_k))
262			goto no_context;
263
264		/*
265		 * Since the vmalloc area is global, it is unnecessary
266		 * to copy individual PTEs
267		 */
268		pmd = pmd_offset(pud, addr);
269		pmd_k = pmd_offset(pud_k, addr);
270		if (!pmd_present(*pmd_k))
271			goto no_context;
272		set_pmd(pmd, *pmd_k);
273
274		/*
275		 * Make sure the actual PTE exists as well to
276		 * catch kernel vmalloc-area accesses to non-mapped
277		 * addresses. If we don't do this, this will just
278		 * silently loop forever.
279		 */
280		pte_k = pte_offset_kernel(pmd_k, addr);
281		if (!pte_present(*pte_k))
282			goto no_context;
283		return;
284	}
285}