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Linux/arch/xtensa/mm/fault.c

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  1 // TODO VM_EXEC flag work-around, cache aliasing
  2 /*
  3  * arch/xtensa/mm/fault.c
  4  *
  5  * This file is subject to the terms and conditions of the GNU General Public
  6  * License.  See the file "COPYING" in the main directory of this archive
  7  * for more details.
  8  *
  9  * Copyright (C) 2001 - 2010 Tensilica Inc.
 10  *
 11  * Chris Zankel <chris@zankel.net>
 12  * Joe Taylor   <joe@tensilica.com, joetylr@yahoo.com>
 13  */
 14 
 15 #include <linux/mm.h>
 16 #include <linux/extable.h>
 17 #include <linux/hardirq.h>
 18 #include <linux/perf_event.h>
 19 #include <linux/uaccess.h>
 20 #include <asm/mmu_context.h>
 21 #include <asm/cacheflush.h>
 22 #include <asm/hardirq.h>
 23 #include <asm/pgalloc.h>
 24 
 25 DEFINE_PER_CPU(unsigned long, asid_cache) = ASID_USER_FIRST;
 26 void bad_page_fault(struct pt_regs*, unsigned long, int);
 27 
 28 /*
 29  * This routine handles page faults.  It determines the address,
 30  * and the problem, and then passes it off to one of the appropriate
 31  * routines.
 32  *
 33  * Note: does not handle Miss and MultiHit.
 34  */
 35 
 36 void do_page_fault(struct pt_regs *regs)
 37 {
 38         struct vm_area_struct * vma;
 39         struct mm_struct *mm = current->mm;
 40         unsigned int exccause = regs->exccause;
 41         unsigned int address = regs->excvaddr;
 42         int code;
 43 
 44         int is_write, is_exec;
 45         vm_fault_t fault;
 46         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 47 
 48         code = SEGV_MAPERR;
 49 
 50         /* We fault-in kernel-space virtual memory on-demand. The
 51          * 'reference' page table is init_mm.pgd.
 52          */
 53         if (address >= TASK_SIZE && !user_mode(regs))
 54                 goto vmalloc_fault;
 55 
 56         /* If we're in an interrupt or have no user
 57          * context, we must not take the fault..
 58          */
 59         if (faulthandler_disabled() || !mm) {
 60                 bad_page_fault(regs, address, SIGSEGV);
 61                 return;
 62         }
 63 
 64         is_write = (exccause == EXCCAUSE_STORE_CACHE_ATTRIBUTE) ? 1 : 0;
 65         is_exec =  (exccause == EXCCAUSE_ITLB_PRIVILEGE ||
 66                     exccause == EXCCAUSE_ITLB_MISS ||
 67                     exccause == EXCCAUSE_FETCH_CACHE_ATTRIBUTE) ? 1 : 0;
 68 
 69         pr_debug("[%s:%d:%08x:%d:%08lx:%s%s]\n",
 70                  current->comm, current->pid,
 71                  address, exccause, regs->pc,
 72                  is_write ? "w" : "", is_exec ? "x" : "");
 73 
 74         if (user_mode(regs))
 75                 flags |= FAULT_FLAG_USER;
 76 retry:
 77         down_read(&mm->mmap_sem);
 78         vma = find_vma(mm, address);
 79 
 80         if (!vma)
 81                 goto bad_area;
 82         if (vma->vm_start <= address)
 83                 goto good_area;
 84         if (!(vma->vm_flags & VM_GROWSDOWN))
 85                 goto bad_area;
 86         if (expand_stack(vma, address))
 87                 goto bad_area;
 88 
 89         /* Ok, we have a good vm_area for this memory access, so
 90          * we can handle it..
 91          */
 92 
 93 good_area:
 94         code = SEGV_ACCERR;
 95 
 96         if (is_write) {
 97                 if (!(vma->vm_flags & VM_WRITE))
 98                         goto bad_area;
 99                 flags |= FAULT_FLAG_WRITE;
100         } else if (is_exec) {
101                 if (!(vma->vm_flags & VM_EXEC))
102                         goto bad_area;
103         } else  /* Allow read even from write-only pages. */
104                 if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
105                         goto bad_area;
106 
107         /* If for any reason at all we couldn't handle the fault,
108          * make sure we exit gracefully rather than endlessly redo
109          * the fault.
110          */
111         fault = handle_mm_fault(vma, address, flags);
112 
113         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
114                 return;
115 
116         if (unlikely(fault & VM_FAULT_ERROR)) {
117                 if (fault & VM_FAULT_OOM)
118                         goto out_of_memory;
119                 else if (fault & VM_FAULT_SIGSEGV)
120                         goto bad_area;
121                 else if (fault & VM_FAULT_SIGBUS)
122                         goto do_sigbus;
123                 BUG();
124         }
125         if (flags & FAULT_FLAG_ALLOW_RETRY) {
126                 if (fault & VM_FAULT_MAJOR)
127                         current->maj_flt++;
128                 else
129                         current->min_flt++;
130                 if (fault & VM_FAULT_RETRY) {
131                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
132                         flags |= FAULT_FLAG_TRIED;
133 
134                          /* No need to up_read(&mm->mmap_sem) as we would
135                          * have already released it in __lock_page_or_retry
136                          * in mm/filemap.c.
137                          */
138 
139                         goto retry;
140                 }
141         }
142 
143         up_read(&mm->mmap_sem);
144         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
145         if (flags & VM_FAULT_MAJOR)
146                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
147         else
148                 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
149 
150         return;
151 
152         /* Something tried to access memory that isn't in our memory map..
153          * Fix it, but check if it's kernel or user first..
154          */
155 bad_area:
156         up_read(&mm->mmap_sem);
157         if (user_mode(regs)) {
158                 current->thread.bad_vaddr = address;
159                 current->thread.error_code = is_write;
160                 force_sig_fault(SIGSEGV, code, (void *) address, current);
161                 return;
162         }
163         bad_page_fault(regs, address, SIGSEGV);
164         return;
165 
166 
167         /* We ran out of memory, or some other thing happened to us that made
168          * us unable to handle the page fault gracefully.
169          */
170 out_of_memory:
171         up_read(&mm->mmap_sem);
172         if (!user_mode(regs))
173                 bad_page_fault(regs, address, SIGKILL);
174         else
175                 pagefault_out_of_memory();
176         return;
177 
178 do_sigbus:
179         up_read(&mm->mmap_sem);
180 
181         /* Send a sigbus, regardless of whether we were in kernel
182          * or user mode.
183          */
184         current->thread.bad_vaddr = address;
185         force_sig_fault(SIGBUS, BUS_ADRERR, (void *) address, current);
186 
187         /* Kernel mode? Handle exceptions or die */
188         if (!user_mode(regs))
189                 bad_page_fault(regs, address, SIGBUS);
190         return;
191 
192 vmalloc_fault:
193         {
194                 /* Synchronize this task's top level page-table
195                  * with the 'reference' page table.
196                  */
197                 struct mm_struct *act_mm = current->active_mm;
198                 int index = pgd_index(address);
199                 pgd_t *pgd, *pgd_k;
200                 pmd_t *pmd, *pmd_k;
201                 pte_t *pte_k;
202 
203                 if (act_mm == NULL)
204                         goto bad_page_fault;
205 
206                 pgd = act_mm->pgd + index;
207                 pgd_k = init_mm.pgd + index;
208 
209                 if (!pgd_present(*pgd_k))
210                         goto bad_page_fault;
211 
212                 pgd_val(*pgd) = pgd_val(*pgd_k);
213 
214                 pmd = pmd_offset(pgd, address);
215                 pmd_k = pmd_offset(pgd_k, address);
216                 if (!pmd_present(*pmd) || !pmd_present(*pmd_k))
217                         goto bad_page_fault;
218 
219                 pmd_val(*pmd) = pmd_val(*pmd_k);
220                 pte_k = pte_offset_kernel(pmd_k, address);
221 
222                 if (!pte_present(*pte_k))
223                         goto bad_page_fault;
224                 return;
225         }
226 bad_page_fault:
227         bad_page_fault(regs, address, SIGKILL);
228         return;
229 }
230 
231 
232 void
233 bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
234 {
235         extern void die(const char*, struct pt_regs*, long);
236         const struct exception_table_entry *entry;
237 
238         /* Are we prepared to handle this kernel fault?  */
239         if ((entry = search_exception_tables(regs->pc)) != NULL) {
240                 pr_debug("%s: Exception at pc=%#010lx (%lx)\n",
241                          current->comm, regs->pc, entry->fixup);
242                 current->thread.bad_uaddr = address;
243                 regs->pc = entry->fixup;
244                 return;
245         }
246 
247         /* Oops. The kernel tried to access some bad page. We'll have to
248          * terminate things with extreme prejudice.
249          */
250         pr_alert("Unable to handle kernel paging request at virtual "
251                  "address %08lx\n pc = %08lx, ra = %08lx\n",
252                  address, regs->pc, regs->areg[0]);
253         die("Oops", regs, sig);
254         do_exit(sig);
255 }
256 

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