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Linux/arch/m68k/sun3/mmu_emu.c

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  1 /*
  2 ** Tablewalk MMU emulator
  3 **
  4 ** by Toshiyasu Morita
  5 **
  6 ** Started 1/16/98 @ 2:22 am
  7 */
  8 
  9 #include <linux/mman.h>
 10 #include <linux/mm.h>
 11 #include <linux/kernel.h>
 12 #include <linux/ptrace.h>
 13 #include <linux/delay.h>
 14 #include <linux/bootmem.h>
 15 #include <linux/bitops.h>
 16 #include <linux/module.h>
 17 
 18 #include <asm/setup.h>
 19 #include <asm/traps.h>
 20 #include <asm/uaccess.h>
 21 #include <asm/page.h>
 22 #include <asm/pgtable.h>
 23 #include <asm/sun3mmu.h>
 24 #include <asm/segment.h>
 25 #include <asm/oplib.h>
 26 #include <asm/mmu_context.h>
 27 #include <asm/dvma.h>
 28 
 29 
 30 #undef DEBUG_MMU_EMU
 31 #define DEBUG_PROM_MAPS
 32 
 33 /*
 34 ** Defines
 35 */
 36 
 37 #define CONTEXTS_NUM            8
 38 #define SEGMAPS_PER_CONTEXT_NUM 2048
 39 #define PAGES_PER_SEGMENT       16
 40 #define PMEGS_NUM               256
 41 #define PMEG_MASK               0xFF
 42 
 43 /*
 44 ** Globals
 45 */
 46 
 47 unsigned long m68k_vmalloc_end;
 48 EXPORT_SYMBOL(m68k_vmalloc_end);
 49 
 50 unsigned long pmeg_vaddr[PMEGS_NUM];
 51 unsigned char pmeg_alloc[PMEGS_NUM];
 52 unsigned char pmeg_ctx[PMEGS_NUM];
 53 
 54 /* pointers to the mm structs for each task in each
 55    context. 0xffffffff is a marker for kernel context */
 56 static struct mm_struct *ctx_alloc[CONTEXTS_NUM] = {
 57     [0] = (struct mm_struct *)0xffffffff
 58 };
 59 
 60 /* has this context been mmdrop'd? */
 61 static unsigned char ctx_avail = CONTEXTS_NUM-1;
 62 
 63 /* array of pages to be marked off for the rom when we do mem_init later */
 64 /* 256 pages lets the rom take up to 2mb of physical ram..  I really
 65    hope it never wants mote than that. */
 66 unsigned long rom_pages[256];
 67 
 68 /* Print a PTE value in symbolic form. For debugging. */
 69 void print_pte (pte_t pte)
 70 {
 71 #if 0
 72         /* Verbose version. */
 73         unsigned long val = pte_val (pte);
 74         printk (" pte=%lx [addr=%lx",
 75                 val, (val & SUN3_PAGE_PGNUM_MASK) << PAGE_SHIFT);
 76         if (val & SUN3_PAGE_VALID)      printk (" valid");
 77         if (val & SUN3_PAGE_WRITEABLE)  printk (" write");
 78         if (val & SUN3_PAGE_SYSTEM)     printk (" sys");
 79         if (val & SUN3_PAGE_NOCACHE)    printk (" nocache");
 80         if (val & SUN3_PAGE_ACCESSED)   printk (" accessed");
 81         if (val & SUN3_PAGE_MODIFIED)   printk (" modified");
 82         switch (val & SUN3_PAGE_TYPE_MASK) {
 83                 case SUN3_PAGE_TYPE_MEMORY: printk (" memory"); break;
 84                 case SUN3_PAGE_TYPE_IO:     printk (" io");     break;
 85                 case SUN3_PAGE_TYPE_VME16:  printk (" vme16");  break;
 86                 case SUN3_PAGE_TYPE_VME32:  printk (" vme32");  break;
 87         }
 88         printk ("]\n");
 89 #else
 90         /* Terse version. More likely to fit on a line. */
 91         unsigned long val = pte_val (pte);
 92         char flags[7], *type;
 93 
 94         flags[0] = (val & SUN3_PAGE_VALID)     ? 'v' : '-';
 95         flags[1] = (val & SUN3_PAGE_WRITEABLE) ? 'w' : '-';
 96         flags[2] = (val & SUN3_PAGE_SYSTEM)    ? 's' : '-';
 97         flags[3] = (val & SUN3_PAGE_NOCACHE)   ? 'x' : '-';
 98         flags[4] = (val & SUN3_PAGE_ACCESSED)  ? 'a' : '-';
 99         flags[5] = (val & SUN3_PAGE_MODIFIED)  ? 'm' : '-';
100         flags[6] = '\0';
101 
102         switch (val & SUN3_PAGE_TYPE_MASK) {
103                 case SUN3_PAGE_TYPE_MEMORY: type = "memory"; break;
104                 case SUN3_PAGE_TYPE_IO:     type = "io"    ; break;
105                 case SUN3_PAGE_TYPE_VME16:  type = "vme16" ; break;
106                 case SUN3_PAGE_TYPE_VME32:  type = "vme32" ; break;
107                 default: type = "unknown?"; break;
108         }
109 
110         printk (" pte=%08lx [%07lx %s %s]\n",
111                 val, (val & SUN3_PAGE_PGNUM_MASK) << PAGE_SHIFT, flags, type);
112 #endif
113 }
114 
115 /* Print the PTE value for a given virtual address. For debugging. */
116 void print_pte_vaddr (unsigned long vaddr)
117 {
118         printk (" vaddr=%lx [%02lx]", vaddr, sun3_get_segmap (vaddr));
119         print_pte (__pte (sun3_get_pte (vaddr)));
120 }
121 
122 /*
123  * Initialise the MMU emulator.
124  */
125 void mmu_emu_init(unsigned long bootmem_end)
126 {
127         unsigned long seg, num;
128         int i,j;
129 
130         memset(rom_pages, 0, sizeof(rom_pages));
131         memset(pmeg_vaddr, 0, sizeof(pmeg_vaddr));
132         memset(pmeg_alloc, 0, sizeof(pmeg_alloc));
133         memset(pmeg_ctx, 0, sizeof(pmeg_ctx));
134 
135         /* pmeg align the end of bootmem, adding another pmeg,
136          * later bootmem allocations will likely need it */
137         bootmem_end = (bootmem_end + (2 * SUN3_PMEG_SIZE)) & ~SUN3_PMEG_MASK;
138 
139         /* mark all of the pmegs used thus far as reserved */
140         for (i=0; i < __pa(bootmem_end) / SUN3_PMEG_SIZE ; ++i)
141                 pmeg_alloc[i] = 2;
142 
143 
144         /* I'm thinking that most of the top pmeg's are going to be
145            used for something, and we probably shouldn't risk it */
146         for(num = 0xf0; num <= 0xff; num++)
147                 pmeg_alloc[num] = 2;
148 
149         /* liberate all existing mappings in the rest of kernel space */
150         for(seg = bootmem_end; seg < 0x0f800000; seg += SUN3_PMEG_SIZE) {
151                 i = sun3_get_segmap(seg);
152 
153                 if(!pmeg_alloc[i]) {
154 #ifdef DEBUG_MMU_EMU
155                         printk("freed: ");
156                         print_pte_vaddr (seg);
157 #endif
158                         sun3_put_segmap(seg, SUN3_INVALID_PMEG);
159                 }
160         }
161 
162         j = 0;
163         for (num=0, seg=0x0F800000; seg<0x10000000; seg+=16*PAGE_SIZE) {
164                 if (sun3_get_segmap (seg) != SUN3_INVALID_PMEG) {
165 #ifdef DEBUG_PROM_MAPS
166                         for(i = 0; i < 16; i++) {
167                                 printk ("mapped:");
168                                 print_pte_vaddr (seg + (i*PAGE_SIZE));
169                                 break;
170                         }
171 #endif
172                         // the lowest mapping here is the end of our
173                         // vmalloc region
174                         if (!m68k_vmalloc_end)
175                                 m68k_vmalloc_end = seg;
176 
177                         // mark the segmap alloc'd, and reserve any
178                         // of the first 0xbff pages the hardware is
179                         // already using...  does any sun3 support > 24mb?
180                         pmeg_alloc[sun3_get_segmap(seg)] = 2;
181                 }
182         }
183 
184         dvma_init();
185 
186 
187         /* blank everything below the kernel, and we've got the base
188            mapping to start all the contexts off with... */
189         for(seg = 0; seg < PAGE_OFFSET; seg += SUN3_PMEG_SIZE)
190                 sun3_put_segmap(seg, SUN3_INVALID_PMEG);
191 
192         set_fs(MAKE_MM_SEG(3));
193         for(seg = 0; seg < 0x10000000; seg += SUN3_PMEG_SIZE) {
194                 i = sun3_get_segmap(seg);
195                 for(j = 1; j < CONTEXTS_NUM; j++)
196                         (*(romvec->pv_setctxt))(j, (void *)seg, i);
197         }
198         set_fs(KERNEL_DS);
199 
200 }
201 
202 /* erase the mappings for a dead context.  Uses the pg_dir for hints
203    as the pmeg tables proved somewhat unreliable, and unmapping all of
204    TASK_SIZE was much slower and no more stable. */
205 /* todo: find a better way to keep track of the pmegs used by a
206    context for when they're cleared */
207 void clear_context(unsigned long context)
208 {
209      unsigned char oldctx;
210      unsigned long i;
211 
212      if(context) {
213              if(!ctx_alloc[context])
214                      panic("clear_context: context not allocated\n");
215 
216              ctx_alloc[context]->context = SUN3_INVALID_CONTEXT;
217              ctx_alloc[context] = (struct mm_struct *)0;
218              ctx_avail++;
219      }
220 
221      oldctx = sun3_get_context();
222 
223      sun3_put_context(context);
224 
225      for(i = 0; i < SUN3_INVALID_PMEG; i++) {
226              if((pmeg_ctx[i] == context) && (pmeg_alloc[i] == 1)) {
227                      sun3_put_segmap(pmeg_vaddr[i], SUN3_INVALID_PMEG);
228                      pmeg_ctx[i] = 0;
229                      pmeg_alloc[i] = 0;
230                      pmeg_vaddr[i] = 0;
231              }
232      }
233 
234      sun3_put_context(oldctx);
235 }
236 
237 /* gets an empty context.  if full, kills the next context listed to
238    die first */
239 /* This context invalidation scheme is, well, totally arbitrary, I'm
240    sure it could be much more intelligent...  but it gets the job done
241    for now without much overhead in making it's decision. */
242 /* todo: come up with optimized scheme for flushing contexts */
243 unsigned long get_free_context(struct mm_struct *mm)
244 {
245         unsigned long new = 1;
246         static unsigned char next_to_die = 1;
247 
248         if(!ctx_avail) {
249                 /* kill someone to get our context */
250                 new = next_to_die;
251                 clear_context(new);
252                 next_to_die = (next_to_die + 1) & 0x7;
253                 if(!next_to_die)
254                         next_to_die++;
255         } else {
256                 while(new < CONTEXTS_NUM) {
257                         if(ctx_alloc[new])
258                                 new++;
259                         else
260                                 break;
261                 }
262                 // check to make sure one was really free...
263                 if(new == CONTEXTS_NUM)
264                         panic("get_free_context: failed to find free context");
265         }
266 
267         ctx_alloc[new] = mm;
268         ctx_avail--;
269 
270         return new;
271 }
272 
273 /*
274  * Dynamically select a `spare' PMEG and use it to map virtual `vaddr' in
275  * `context'. Maintain internal PMEG management structures. This doesn't
276  * actually map the physical address, but does clear the old mappings.
277  */
278 //todo: better allocation scheme? but is extra complexity worthwhile?
279 //todo: only clear old entries if necessary? how to tell?
280 
281 inline void mmu_emu_map_pmeg (int context, int vaddr)
282 {
283         static unsigned char curr_pmeg = 128;
284         int i;
285 
286         /* Round address to PMEG boundary. */
287         vaddr &= ~SUN3_PMEG_MASK;
288 
289         /* Find a spare one. */
290         while (pmeg_alloc[curr_pmeg] == 2)
291                 ++curr_pmeg;
292 
293 
294 #ifdef DEBUG_MMU_EMU
295 printk("mmu_emu_map_pmeg: pmeg %x to context %d vaddr %x\n",
296        curr_pmeg, context, vaddr);
297 #endif
298 
299         /* Invalidate old mapping for the pmeg, if any */
300         if (pmeg_alloc[curr_pmeg] == 1) {
301                 sun3_put_context(pmeg_ctx[curr_pmeg]);
302                 sun3_put_segmap (pmeg_vaddr[curr_pmeg], SUN3_INVALID_PMEG);
303                 sun3_put_context(context);
304         }
305 
306         /* Update PMEG management structures. */
307         // don't take pmeg's away from the kernel...
308         if(vaddr >= PAGE_OFFSET) {
309                 /* map kernel pmegs into all contexts */
310                 unsigned char i;
311 
312                 for(i = 0; i < CONTEXTS_NUM; i++) {
313                         sun3_put_context(i);
314                         sun3_put_segmap (vaddr, curr_pmeg);
315                 }
316                 sun3_put_context(context);
317                 pmeg_alloc[curr_pmeg] = 2;
318                 pmeg_ctx[curr_pmeg] = 0;
319 
320         }
321         else {
322                 pmeg_alloc[curr_pmeg] = 1;
323                 pmeg_ctx[curr_pmeg] = context;
324                 sun3_put_segmap (vaddr, curr_pmeg);
325 
326         }
327         pmeg_vaddr[curr_pmeg] = vaddr;
328 
329         /* Set hardware mapping and clear the old PTE entries. */
330         for (i=0; i<SUN3_PMEG_SIZE; i+=SUN3_PTE_SIZE)
331                 sun3_put_pte (vaddr + i, SUN3_PAGE_SYSTEM);
332 
333         /* Consider a different one next time. */
334         ++curr_pmeg;
335 }
336 
337 /*
338  * Handle a pagefault at virtual address `vaddr'; check if there should be a
339  * page there (specifically, whether the software pagetables indicate that
340  * there is). This is necessary due to the limited size of the second-level
341  * Sun3 hardware pagetables (256 groups of 16 pages). If there should be a
342  * mapping present, we select a `spare' PMEG and use it to create a mapping.
343  * `read_flag' is nonzero for a read fault; zero for a write. Returns nonzero
344  * if we successfully handled the fault.
345  */
346 //todo: should we bump minor pagefault counter? if so, here or in caller?
347 //todo: possibly inline this into bus_error030 in <asm/buserror.h> ?
348 
349 // kernel_fault is set when a kernel page couldn't be demand mapped,
350 // and forces another try using the kernel page table.  basically a
351 // hack so that vmalloc would work correctly.
352 
353 int mmu_emu_handle_fault (unsigned long vaddr, int read_flag, int kernel_fault)
354 {
355         unsigned long segment, offset;
356         unsigned char context;
357         pte_t *pte;
358         pgd_t * crp;
359 
360         if(current->mm == NULL) {
361                 crp = swapper_pg_dir;
362                 context = 0;
363         } else {
364                 context = current->mm->context;
365                 if(kernel_fault)
366                         crp = swapper_pg_dir;
367                 else
368                         crp = current->mm->pgd;
369         }
370 
371 #ifdef DEBUG_MMU_EMU
372         printk ("mmu_emu_handle_fault: vaddr=%lx type=%s crp=%p\n",
373                 vaddr, read_flag ? "read" : "write", crp);
374 #endif
375 
376         segment = (vaddr >> SUN3_PMEG_SIZE_BITS) & 0x7FF;
377         offset  = (vaddr >> SUN3_PTE_SIZE_BITS) & 0xF;
378 
379 #ifdef DEBUG_MMU_EMU
380         printk ("mmu_emu_handle_fault: segment=%lx offset=%lx\n", segment, offset);
381 #endif
382 
383         pte = (pte_t *) pgd_val (*(crp + segment));
384 
385 //todo: next line should check for valid pmd properly.
386         if (!pte) {
387 //                printk ("mmu_emu_handle_fault: invalid pmd\n");
388                 return 0;
389         }
390 
391         pte = (pte_t *) __va ((unsigned long)(pte + offset));
392 
393         /* Make sure this is a valid page */
394         if (!(pte_val (*pte) & SUN3_PAGE_VALID))
395                 return 0;
396 
397         /* Make sure there's a pmeg allocated for the page */
398         if (sun3_get_segmap (vaddr&~SUN3_PMEG_MASK) == SUN3_INVALID_PMEG)
399                 mmu_emu_map_pmeg (context, vaddr);
400 
401         /* Write the pte value to hardware MMU */
402         sun3_put_pte (vaddr&PAGE_MASK, pte_val (*pte));
403 
404         /* Update software copy of the pte value */
405 // I'm not sure this is necessary. If this is required, we ought to simply
406 // copy this out when we reuse the PMEG or at some other convenient time.
407 // Doing it here is fairly meaningless, anyway, as we only know about the
408 // first access to a given page. --m
409         if (!read_flag) {
410                 if (pte_val (*pte) & SUN3_PAGE_WRITEABLE)
411                         pte_val (*pte) |= (SUN3_PAGE_ACCESSED
412                                            | SUN3_PAGE_MODIFIED);
413                 else
414                         return 0;       /* Write-protect error. */
415         } else
416                 pte_val (*pte) |= SUN3_PAGE_ACCESSED;
417 
418 #ifdef DEBUG_MMU_EMU
419         printk ("seg:%d crp:%p ->", get_fs().seg, crp);
420         print_pte_vaddr (vaddr);
421         printk ("\n");
422 #endif
423 
424         return 1;
425 }
426 

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