xref: /openbmc/qemu/bsd-user/mmap.c (revision 36d5d891559f6b9f0bae4907669de9bfdf5d4d94)
1 /*
2  *  mmap support for qemu
3  *
4  *  Copyright (c) 2003 - 2008 Fabrice Bellard
5  *
6  *  This program is free software; you can redistribute it and/or modify
7  *  it under the terms of the GNU General Public License as published by
8  *  the Free Software Foundation; either version 2 of the License, or
9  *  (at your option) any later version.
10  *
11  *  This program is distributed in the hope that it will be useful,
12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  *  GNU General Public License for more details.
15  *
16  *  You should have received a copy of the GNU General Public License
17  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
18  */
19 #include "qemu/osdep.h"
20 
21 #include "qemu.h"
22 #include "qemu-common.h"
23 
24 //#define DEBUG_MMAP
25 
26 static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
27 static __thread int mmap_lock_count;
28 
29 void mmap_lock(void)
30 {
31     if (mmap_lock_count++ == 0) {
32         pthread_mutex_lock(&mmap_mutex);
33     }
34 }
35 
36 void mmap_unlock(void)
37 {
38     if (--mmap_lock_count == 0) {
39         pthread_mutex_unlock(&mmap_mutex);
40     }
41 }
42 
43 bool have_mmap_lock(void)
44 {
45     return mmap_lock_count > 0 ? true : false;
46 }
47 
48 /* Grab lock to make sure things are in a consistent state after fork().  */
49 void mmap_fork_start(void)
50 {
51     if (mmap_lock_count)
52         abort();
53     pthread_mutex_lock(&mmap_mutex);
54 }
55 
56 void mmap_fork_end(int child)
57 {
58     if (child)
59         pthread_mutex_init(&mmap_mutex, NULL);
60     else
61         pthread_mutex_unlock(&mmap_mutex);
62 }
63 
64 /* NOTE: all the constants are the HOST ones, but addresses are target. */
65 int target_mprotect(abi_ulong start, abi_ulong len, int prot)
66 {
67     abi_ulong end, host_start, host_end, addr;
68     int prot1, ret;
69 
70 #ifdef DEBUG_MMAP
71     printf("mprotect: start=0x" TARGET_ABI_FMT_lx
72            "len=0x" TARGET_ABI_FMT_lx " prot=%c%c%c\n", start, len,
73            prot & PROT_READ ? 'r' : '-',
74            prot & PROT_WRITE ? 'w' : '-',
75            prot & PROT_EXEC ? 'x' : '-');
76 #endif
77 
78     if ((start & ~TARGET_PAGE_MASK) != 0)
79         return -EINVAL;
80     len = TARGET_PAGE_ALIGN(len);
81     end = start + len;
82     if (end < start)
83         return -EINVAL;
84     prot &= PROT_READ | PROT_WRITE | PROT_EXEC;
85     if (len == 0)
86         return 0;
87 
88     mmap_lock();
89     host_start = start & qemu_host_page_mask;
90     host_end = HOST_PAGE_ALIGN(end);
91     if (start > host_start) {
92         /* handle host page containing start */
93         prot1 = prot;
94         for (addr = host_start; addr < start; addr += TARGET_PAGE_SIZE) {
95             prot1 |= page_get_flags(addr);
96         }
97         if (host_end == host_start + qemu_host_page_size) {
98             for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
99                 prot1 |= page_get_flags(addr);
100             }
101             end = host_end;
102         }
103         ret = mprotect(g2h_untagged(host_start),
104                        qemu_host_page_size, prot1 & PAGE_BITS);
105         if (ret != 0)
106             goto error;
107         host_start += qemu_host_page_size;
108     }
109     if (end < host_end) {
110         prot1 = prot;
111         for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
112             prot1 |= page_get_flags(addr);
113         }
114         ret = mprotect(g2h_untagged(host_end - qemu_host_page_size),
115                        qemu_host_page_size, prot1 & PAGE_BITS);
116         if (ret != 0)
117             goto error;
118         host_end -= qemu_host_page_size;
119     }
120 
121     /* handle the pages in the middle */
122     if (host_start < host_end) {
123         ret = mprotect(g2h_untagged(host_start), host_end - host_start, prot);
124         if (ret != 0)
125             goto error;
126     }
127     page_set_flags(start, start + len, prot | PAGE_VALID);
128     mmap_unlock();
129     return 0;
130 error:
131     mmap_unlock();
132     return ret;
133 }
134 
135 /* map an incomplete host page */
136 static int mmap_frag(abi_ulong real_start,
137                      abi_ulong start, abi_ulong end,
138                      int prot, int flags, int fd, abi_ulong offset)
139 {
140     abi_ulong real_end, addr;
141     void *host_start;
142     int prot1, prot_new;
143 
144     real_end = real_start + qemu_host_page_size;
145     host_start = g2h_untagged(real_start);
146 
147     /* get the protection of the target pages outside the mapping */
148     prot1 = 0;
149     for (addr = real_start; addr < real_end; addr++) {
150         if (addr < start || addr >= end)
151             prot1 |= page_get_flags(addr);
152     }
153 
154     if (prot1 == 0) {
155         /* no page was there, so we allocate one */
156         void *p = mmap(host_start, qemu_host_page_size, prot,
157                        flags | MAP_ANON, -1, 0);
158         if (p == MAP_FAILED)
159             return -1;
160         prot1 = prot;
161     }
162     prot1 &= PAGE_BITS;
163 
164     prot_new = prot | prot1;
165     if (!(flags & MAP_ANON)) {
166         /* msync() won't work here, so we return an error if write is
167            possible while it is a shared mapping */
168         if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED &&
169             (prot & PROT_WRITE))
170             return -1;
171 
172         /* adjust protection to be able to read */
173         if (!(prot1 & PROT_WRITE))
174             mprotect(host_start, qemu_host_page_size, prot1 | PROT_WRITE);
175 
176         /* read the corresponding file data */
177         if (pread(fd, g2h_untagged(start), end - start, offset) == -1) {
178             return -1;
179         }
180 
181         /* put final protection */
182         if (prot_new != (prot1 | PROT_WRITE))
183             mprotect(host_start, qemu_host_page_size, prot_new);
184     } else {
185         if (prot_new != prot1) {
186             mprotect(host_start, qemu_host_page_size, prot_new);
187         }
188         if (prot_new & PROT_WRITE) {
189             memset(g2h_untagged(start), 0, end - start);
190         }
191     }
192     return 0;
193 }
194 
195 #if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
196 # define TASK_UNMAPPED_BASE  (1ul << 38)
197 #else
198 # define TASK_UNMAPPED_BASE  0x40000000
199 #endif
200 abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
201 
202 unsigned long last_brk;
203 
204 /*
205  * Subroutine of mmap_find_vma, used when we have pre-allocated a chunk of guest
206  * address space.
207  */
208 static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size,
209                                         abi_ulong alignment)
210 {
211     abi_ulong addr;
212     abi_ulong end_addr;
213     int prot;
214     int looped = 0;
215 
216     if (size > reserved_va) {
217         return (abi_ulong)-1;
218     }
219 
220     size = HOST_PAGE_ALIGN(size) + alignment;
221     end_addr = start + size;
222     if (end_addr > reserved_va) {
223         end_addr = reserved_va;
224     }
225     addr = end_addr - qemu_host_page_size;
226 
227     while (1) {
228         if (addr > end_addr) {
229             if (looped) {
230                 return (abi_ulong)-1;
231             }
232             end_addr = reserved_va;
233             addr = end_addr - qemu_host_page_size;
234             looped = 1;
235             continue;
236         }
237         prot = page_get_flags(addr);
238         if (prot) {
239             end_addr = addr;
240         }
241         if (end_addr - addr >= size) {
242             break;
243         }
244         addr -= qemu_host_page_size;
245     }
246 
247     if (start == mmap_next_start) {
248         mmap_next_start = addr;
249     }
250     /* addr is sufficiently low to align it up */
251     if (alignment != 0) {
252         addr = (addr + alignment) & ~(alignment - 1);
253     }
254     return addr;
255 }
256 
257 /*
258  * Find and reserve a free memory area of size 'size'. The search
259  * starts at 'start'.
260  * It must be called with mmap_lock() held.
261  * Return -1 if error.
262  */
263 static abi_ulong mmap_find_vma_aligned(abi_ulong start, abi_ulong size,
264                                        abi_ulong alignment)
265 {
266     void *ptr, *prev;
267     abi_ulong addr;
268     int flags;
269     int wrapped, repeat;
270 
271     /* If 'start' == 0, then a default start address is used. */
272     if (start == 0) {
273         start = mmap_next_start;
274     } else {
275         start &= qemu_host_page_mask;
276     }
277 
278     size = HOST_PAGE_ALIGN(size);
279 
280     if (reserved_va) {
281         return mmap_find_vma_reserved(start, size,
282             (alignment != 0 ? 1 << alignment : 0));
283     }
284 
285     addr = start;
286     wrapped = repeat = 0;
287     prev = 0;
288     flags = MAP_ANONYMOUS | MAP_PRIVATE;
289     if (alignment != 0) {
290         flags |= MAP_ALIGNED(alignment);
291     }
292 
293     for (;; prev = ptr) {
294         /*
295          * Reserve needed memory area to avoid a race.
296          * It should be discarded using:
297          *  - mmap() with MAP_FIXED flag
298          *  - mremap() with MREMAP_FIXED flag
299          *  - shmat() with SHM_REMAP flag
300          */
301         ptr = mmap(g2h_untagged(addr), size, PROT_NONE,
302                    flags, -1, 0);
303 
304         /* ENOMEM, if host address space has no memory */
305         if (ptr == MAP_FAILED) {
306             return (abi_ulong)-1;
307         }
308 
309         /*
310          * Count the number of sequential returns of the same address.
311          * This is used to modify the search algorithm below.
312          */
313         repeat = (ptr == prev ? repeat + 1 : 0);
314 
315         if (h2g_valid(ptr + size - 1)) {
316             addr = h2g(ptr);
317 
318             if ((addr & ~TARGET_PAGE_MASK) == 0) {
319                 /* Success.  */
320                 if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
321                     mmap_next_start = addr + size;
322                 }
323                 return addr;
324             }
325 
326             /* The address is not properly aligned for the target.  */
327             switch (repeat) {
328             case 0:
329                 /*
330                  * Assume the result that the kernel gave us is the
331                  * first with enough free space, so start again at the
332                  * next higher target page.
333                  */
334                 addr = TARGET_PAGE_ALIGN(addr);
335                 break;
336             case 1:
337                 /*
338                  * Sometimes the kernel decides to perform the allocation
339                  * at the top end of memory instead.
340                  */
341                 addr &= TARGET_PAGE_MASK;
342                 break;
343             case 2:
344                 /* Start over at low memory.  */
345                 addr = 0;
346                 break;
347             default:
348                 /* Fail.  This unaligned block must the last.  */
349                 addr = -1;
350                 break;
351             }
352         } else {
353             /*
354              * Since the result the kernel gave didn't fit, start
355              * again at low memory.  If any repetition, fail.
356              */
357             addr = (repeat ? -1 : 0);
358         }
359 
360         /* Unmap and try again.  */
361         munmap(ptr, size);
362 
363         /* ENOMEM if we checked the whole of the target address space.  */
364         if (addr == (abi_ulong)-1) {
365             return (abi_ulong)-1;
366         } else if (addr == 0) {
367             if (wrapped) {
368                 return (abi_ulong)-1;
369             }
370             wrapped = 1;
371             /*
372              * Don't actually use 0 when wrapping, instead indicate
373              * that we'd truly like an allocation in low memory.
374              */
375             addr = TARGET_PAGE_SIZE;
376         } else if (wrapped && addr >= start) {
377             return (abi_ulong)-1;
378         }
379     }
380 }
381 
382 abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
383 {
384     return mmap_find_vma_aligned(start, size, 0);
385 }
386 
387 /* NOTE: all the constants are the HOST ones */
388 abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
389                      int flags, int fd, off_t offset)
390 {
391     abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;
392 
393     mmap_lock();
394 #ifdef DEBUG_MMAP
395     {
396         printf("mmap: start=0x" TARGET_ABI_FMT_lx
397                " len=0x" TARGET_ABI_FMT_lx " prot=%c%c%c flags=",
398                start, len,
399                prot & PROT_READ ? 'r' : '-',
400                prot & PROT_WRITE ? 'w' : '-',
401                prot & PROT_EXEC ? 'x' : '-');
402         if (flags & MAP_ALIGNMENT_MASK) {
403             printf("MAP_ALIGNED(%u) ", (flags & MAP_ALIGNMENT_MASK)
404                     >> MAP_ALIGNMENT_SHIFT);
405         }
406         if (flags & MAP_GUARD) {
407             printf("MAP_GUARD ");
408         }
409         if (flags & MAP_FIXED) {
410             printf("MAP_FIXED ");
411         }
412         if (flags & MAP_ANONYMOUS) {
413             printf("MAP_ANON ");
414         }
415         if (flags & MAP_EXCL) {
416             printf("MAP_EXCL ");
417         }
418         if (flags & MAP_PRIVATE) {
419             printf("MAP_PRIVATE ");
420         }
421         if (flags & MAP_SHARED) {
422             printf("MAP_SHARED ");
423         }
424         if (flags & MAP_NOCORE) {
425             printf("MAP_NOCORE ");
426         }
427         if (flags & MAP_STACK) {
428             printf("MAP_STACK ");
429         }
430         printf("fd=%d offset=0x%llx\n", fd, offset);
431     }
432 #endif
433 
434     if ((flags & MAP_ANONYMOUS) && fd != -1) {
435         errno = EINVAL;
436         goto fail;
437     }
438     if (flags & MAP_STACK) {
439         if ((fd != -1) || ((prot & (PROT_READ | PROT_WRITE)) !=
440                     (PROT_READ | PROT_WRITE))) {
441             errno = EINVAL;
442             goto fail;
443         }
444     }
445     if ((flags & MAP_GUARD) && (prot != PROT_NONE || fd != -1 ||
446         offset != 0 || (flags & (MAP_SHARED | MAP_PRIVATE |
447         /* MAP_PREFAULT | */ /* MAP_PREFAULT not in mman.h */
448         MAP_PREFAULT_READ | MAP_ANON | MAP_STACK)) != 0)) {
449         errno = EINVAL;
450         goto fail;
451     }
452 
453     if (offset & ~TARGET_PAGE_MASK) {
454         errno = EINVAL;
455         goto fail;
456     }
457 
458     len = TARGET_PAGE_ALIGN(len);
459     if (len == 0) {
460         errno = EINVAL;
461         goto fail;
462     }
463     real_start = start & qemu_host_page_mask;
464     host_offset = offset & qemu_host_page_mask;
465 
466     /*
467      * If the user is asking for the kernel to find a location, do that
468      * before we truncate the length for mapping files below.
469      */
470     if (!(flags & MAP_FIXED)) {
471         host_len = len + offset - host_offset;
472         host_len = HOST_PAGE_ALIGN(host_len);
473         if ((flags & MAP_ALIGNMENT_MASK) != 0)
474             start = mmap_find_vma_aligned(real_start, host_len,
475                 (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT);
476         else
477             start = mmap_find_vma(real_start, host_len);
478         if (start == (abi_ulong)-1) {
479             errno = ENOMEM;
480             goto fail;
481         }
482     }
483 
484     /*
485      * When mapping files into a memory area larger than the file, accesses
486      * to pages beyond the file size will cause a SIGBUS.
487      *
488      * For example, if mmaping a file of 100 bytes on a host with 4K pages
489      * emulating a target with 8K pages, the target expects to be able to
490      * access the first 8K. But the host will trap us on any access beyond
491      * 4K.
492      *
493      * When emulating a target with a larger page-size than the hosts, we
494      * may need to truncate file maps at EOF and add extra anonymous pages
495      * up to the targets page boundary.
496      */
497 
498     if ((qemu_real_host_page_size < qemu_host_page_size) && fd != -1) {
499         struct stat sb;
500 
501         if (fstat(fd, &sb) == -1) {
502             goto fail;
503         }
504 
505         /* Are we trying to create a map beyond EOF?.  */
506         if (offset + len > sb.st_size) {
507             /*
508              * If so, truncate the file map at eof aligned with
509              * the hosts real pagesize. Additional anonymous maps
510              * will be created beyond EOF.
511              */
512             len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
513         }
514     }
515 
516     if (!(flags & MAP_FIXED)) {
517         unsigned long host_start;
518         void *p;
519 
520         host_len = len + offset - host_offset;
521         host_len = HOST_PAGE_ALIGN(host_len);
522 
523         /*
524          * Note: we prefer to control the mapping address. It is
525          * especially important if qemu_host_page_size >
526          * qemu_real_host_page_size
527          */
528         p = mmap(g2h_untagged(start), host_len, prot,
529                  flags | MAP_FIXED | ((fd != -1) ? MAP_ANONYMOUS : 0), -1, 0);
530         if (p == MAP_FAILED)
531             goto fail;
532         /* update start so that it points to the file position at 'offset' */
533         host_start = (unsigned long)p;
534         if (fd != -1) {
535             p = mmap(g2h_untagged(start), len, prot,
536                      flags | MAP_FIXED, fd, host_offset);
537             if (p == MAP_FAILED) {
538                 munmap(g2h_untagged(start), host_len);
539                 goto fail;
540             }
541             host_start += offset - host_offset;
542         }
543         start = h2g(host_start);
544     } else {
545         if (start & ~TARGET_PAGE_MASK) {
546             errno = EINVAL;
547             goto fail;
548         }
549         end = start + len;
550         real_end = HOST_PAGE_ALIGN(end);
551 
552         /*
553          * Test if requested memory area fits target address space
554          * It can fail only on 64-bit host with 32-bit target.
555          * On any other target/host host mmap() handles this error correctly.
556          */
557 #if TARGET_ABI_BITS == 32 && HOST_LONG_BITS == 64
558         if ((unsigned long)start + len - 1 > (abi_ulong) -1) {
559             errno = EINVAL;
560             goto fail;
561         }
562 #endif
563 
564         /*
565          * worst case: we cannot map the file because the offset is not
566          * aligned, so we read it
567          */
568         if (!(flags & MAP_ANON) &&
569             (offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
570             /*
571              * msync() won't work here, so we return an error if write is
572              * possible while it is a shared mapping
573              */
574             if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED &&
575                 (prot & PROT_WRITE)) {
576                 errno = EINVAL;
577                 goto fail;
578             }
579             retaddr = target_mmap(start, len, prot | PROT_WRITE,
580                                   MAP_FIXED | MAP_PRIVATE | MAP_ANON,
581                                   -1, 0);
582             if (retaddr == -1)
583                 goto fail;
584             if (pread(fd, g2h_untagged(start), len, offset) == -1) {
585                 goto fail;
586             }
587             if (!(prot & PROT_WRITE)) {
588                 ret = target_mprotect(start, len, prot);
589                 if (ret != 0) {
590                     start = ret;
591                     goto the_end;
592                 }
593             }
594             goto the_end;
595         }
596 
597         /* handle the start of the mapping */
598         if (start > real_start) {
599             if (real_end == real_start + qemu_host_page_size) {
600                 /* one single host page */
601                 ret = mmap_frag(real_start, start, end,
602                                 prot, flags, fd, offset);
603                 if (ret == -1)
604                     goto fail;
605                 goto the_end1;
606             }
607             ret = mmap_frag(real_start, start, real_start + qemu_host_page_size,
608                             prot, flags, fd, offset);
609             if (ret == -1)
610                 goto fail;
611             real_start += qemu_host_page_size;
612         }
613         /* handle the end of the mapping */
614         if (end < real_end) {
615             ret = mmap_frag(real_end - qemu_host_page_size,
616                             real_end - qemu_host_page_size, end,
617                             prot, flags, fd,
618                             offset + real_end - qemu_host_page_size - start);
619             if (ret == -1)
620                 goto fail;
621             real_end -= qemu_host_page_size;
622         }
623 
624         /* map the middle (easier) */
625         if (real_start < real_end) {
626             void *p;
627             unsigned long offset1;
628             if (flags & MAP_ANON)
629                 offset1 = 0;
630             else
631                 offset1 = offset + real_start - start;
632             p = mmap(g2h_untagged(real_start), real_end - real_start,
633                      prot, flags, fd, offset1);
634             if (p == MAP_FAILED)
635                 goto fail;
636         }
637     }
638  the_end1:
639     page_set_flags(start, start + len, prot | PAGE_VALID);
640  the_end:
641 #ifdef DEBUG_MMAP
642     printf("ret=0x" TARGET_ABI_FMT_lx "\n", start);
643     page_dump(stdout);
644     printf("\n");
645 #endif
646     tb_invalidate_phys_range(start, start + len);
647     mmap_unlock();
648     return start;
649 fail:
650     mmap_unlock();
651     return -1;
652 }
653 
654 static void mmap_reserve(abi_ulong start, abi_ulong size)
655 {
656     abi_ulong real_start;
657     abi_ulong real_end;
658     abi_ulong addr;
659     abi_ulong end;
660     int prot;
661 
662     real_start = start & qemu_host_page_mask;
663     real_end = HOST_PAGE_ALIGN(start + size);
664     end = start + size;
665     if (start > real_start) {
666         /* handle host page containing start */
667         prot = 0;
668         for (addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
669             prot |= page_get_flags(addr);
670         }
671         if (real_end == real_start + qemu_host_page_size) {
672             for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
673                 prot |= page_get_flags(addr);
674             }
675             end = real_end;
676         }
677         if (prot != 0) {
678             real_start += qemu_host_page_size;
679         }
680     }
681     if (end < real_end) {
682         prot = 0;
683         for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
684             prot |= page_get_flags(addr);
685         }
686         if (prot != 0) {
687             real_end -= qemu_host_page_size;
688         }
689     }
690     if (real_start != real_end) {
691         mmap(g2h_untagged(real_start), real_end - real_start, PROT_NONE,
692                  MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE,
693                  -1, 0);
694     }
695 }
696 
697 int target_munmap(abi_ulong start, abi_ulong len)
698 {
699     abi_ulong end, real_start, real_end, addr;
700     int prot, ret;
701 
702 #ifdef DEBUG_MMAP
703     printf("munmap: start=0x" TARGET_ABI_FMT_lx " len=0x"
704            TARGET_ABI_FMT_lx "\n",
705            start, len);
706 #endif
707     if (start & ~TARGET_PAGE_MASK)
708         return -EINVAL;
709     len = TARGET_PAGE_ALIGN(len);
710     if (len == 0)
711         return -EINVAL;
712     mmap_lock();
713     end = start + len;
714     real_start = start & qemu_host_page_mask;
715     real_end = HOST_PAGE_ALIGN(end);
716 
717     if (start > real_start) {
718         /* handle host page containing start */
719         prot = 0;
720         for (addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
721             prot |= page_get_flags(addr);
722         }
723         if (real_end == real_start + qemu_host_page_size) {
724             for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
725                 prot |= page_get_flags(addr);
726             }
727             end = real_end;
728         }
729         if (prot != 0)
730             real_start += qemu_host_page_size;
731     }
732     if (end < real_end) {
733         prot = 0;
734         for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
735             prot |= page_get_flags(addr);
736         }
737         if (prot != 0)
738             real_end -= qemu_host_page_size;
739     }
740 
741     ret = 0;
742     /* unmap what we can */
743     if (real_start < real_end) {
744         if (reserved_va) {
745             mmap_reserve(real_start, real_end - real_start);
746         } else {
747             ret = munmap(g2h_untagged(real_start), real_end - real_start);
748         }
749     }
750 
751     if (ret == 0) {
752         page_set_flags(start, start + len, 0);
753         tb_invalidate_phys_range(start, start + len);
754     }
755     mmap_unlock();
756     return ret;
757 }
758 
759 int target_msync(abi_ulong start, abi_ulong len, int flags)
760 {
761     abi_ulong end;
762 
763     if (start & ~TARGET_PAGE_MASK)
764         return -EINVAL;
765     len = TARGET_PAGE_ALIGN(len);
766     end = start + len;
767     if (end < start)
768         return -EINVAL;
769     if (end == start)
770         return 0;
771 
772     start &= qemu_host_page_mask;
773     return msync(g2h_untagged(start), end - start, flags);
774 }
775