2 * mmap support for qemu
4 * Copyright (c) 2003 Fabrice Bellard
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.
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.
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/>.
19 #include "qemu/osdep.h"
23 #include "user-internals.h"
24 #include "user-mmap.h"
26 static pthread_mutex_t mmap_mutex
= PTHREAD_MUTEX_INITIALIZER
;
27 static __thread
int mmap_lock_count
;
31 if (mmap_lock_count
++ == 0) {
32 pthread_mutex_lock(&mmap_mutex
);
36 void mmap_unlock(void)
38 if (--mmap_lock_count
== 0) {
39 pthread_mutex_unlock(&mmap_mutex
);
43 bool have_mmap_lock(void)
45 return mmap_lock_count
> 0 ? true : false;
48 /* Grab lock to make sure things are in a consistent state after fork(). */
49 void mmap_fork_start(void)
53 pthread_mutex_lock(&mmap_mutex
);
56 void mmap_fork_end(int child
)
59 pthread_mutex_init(&mmap_mutex
, NULL
);
61 pthread_mutex_unlock(&mmap_mutex
);
65 * Validate target prot bitmask.
66 * Return the prot bitmask for the host in *HOST_PROT.
67 * Return 0 if the target prot bitmask is invalid, otherwise
68 * the internal qemu page_flags (which will include PAGE_VALID).
70 static int validate_prot_to_pageflags(int *host_prot
, int prot
)
72 int valid
= PROT_READ
| PROT_WRITE
| PROT_EXEC
| TARGET_PROT_SEM
;
73 int page_flags
= (prot
& PAGE_BITS
) | PAGE_VALID
;
76 * For the host, we need not pass anything except read/write/exec.
77 * While PROT_SEM is allowed by all hosts, it is also ignored, so
78 * don't bother transforming guest bit to host bit. Any other
79 * target-specific prot bits will not be understood by the host
80 * and will need to be encoded into page_flags for qemu emulation.
82 * Pages that are executable by the guest will never be executed
83 * by the host, but the host will need to be able to read them.
85 *host_prot
= (prot
& (PROT_READ
| PROT_WRITE
))
86 | (prot
& PROT_EXEC
? PROT_READ
: 0);
90 ARMCPU
*cpu
= ARM_CPU(thread_cpu
);
93 * The PROT_BTI bit is only accepted if the cpu supports the feature.
94 * Since this is the unusual case, don't bother checking unless
95 * the bit has been requested. If set and valid, record the bit
96 * within QEMU's page_flags.
98 if ((prot
& TARGET_PROT_BTI
) && cpu_isar_feature(aa64_bti
, cpu
)) {
99 valid
|= TARGET_PROT_BTI
;
100 page_flags
|= PAGE_BTI
;
102 /* Similarly for the PROT_MTE bit. */
103 if ((prot
& TARGET_PROT_MTE
) && cpu_isar_feature(aa64_mte
, cpu
)) {
104 valid
|= TARGET_PROT_MTE
;
105 page_flags
|= PAGE_MTE
;
110 return prot
& ~valid
? 0 : page_flags
;
113 /* NOTE: all the constants are the HOST ones, but addresses are target. */
114 int target_mprotect(abi_ulong start
, abi_ulong len
, int target_prot
)
116 abi_ulong end
, host_start
, host_end
, addr
;
117 int prot1
, ret
, page_flags
, host_prot
;
119 trace_target_mprotect(start
, len
, target_prot
);
121 if ((start
& ~TARGET_PAGE_MASK
) != 0) {
122 return -TARGET_EINVAL
;
124 page_flags
= validate_prot_to_pageflags(&host_prot
, target_prot
);
126 return -TARGET_EINVAL
;
128 len
= TARGET_PAGE_ALIGN(len
);
130 if (!guest_range_valid_untagged(start
, len
)) {
131 return -TARGET_ENOMEM
;
138 host_start
= start
& qemu_host_page_mask
;
139 host_end
= HOST_PAGE_ALIGN(end
);
140 if (start
> host_start
) {
141 /* handle host page containing start */
143 for (addr
= host_start
; addr
< start
; addr
+= TARGET_PAGE_SIZE
) {
144 prot1
|= page_get_flags(addr
);
146 if (host_end
== host_start
+ qemu_host_page_size
) {
147 for (addr
= end
; addr
< host_end
; addr
+= TARGET_PAGE_SIZE
) {
148 prot1
|= page_get_flags(addr
);
152 ret
= mprotect(g2h_untagged(host_start
), qemu_host_page_size
,
157 host_start
+= qemu_host_page_size
;
159 if (end
< host_end
) {
161 for (addr
= end
; addr
< host_end
; addr
+= TARGET_PAGE_SIZE
) {
162 prot1
|= page_get_flags(addr
);
164 ret
= mprotect(g2h_untagged(host_end
- qemu_host_page_size
),
165 qemu_host_page_size
, prot1
& PAGE_BITS
);
169 host_end
-= qemu_host_page_size
;
172 /* handle the pages in the middle */
173 if (host_start
< host_end
) {
174 ret
= mprotect(g2h_untagged(host_start
),
175 host_end
- host_start
, host_prot
);
181 page_set_flags(start
, start
+ len
, page_flags
);
182 tb_invalidate_phys_range(start
, start
+ len
);
190 /* map an incomplete host page */
191 static int mmap_frag(abi_ulong real_start
,
192 abi_ulong start
, abi_ulong end
,
193 int prot
, int flags
, int fd
, abi_ulong offset
)
195 abi_ulong real_end
, addr
;
199 real_end
= real_start
+ qemu_host_page_size
;
200 host_start
= g2h_untagged(real_start
);
202 /* get the protection of the target pages outside the mapping */
204 for(addr
= real_start
; addr
< real_end
; addr
++) {
205 if (addr
< start
|| addr
>= end
)
206 prot1
|= page_get_flags(addr
);
210 /* no page was there, so we allocate one */
211 void *p
= mmap(host_start
, qemu_host_page_size
, prot
,
212 flags
| MAP_ANONYMOUS
, -1, 0);
219 prot_new
= prot
| prot1
;
220 if (!(flags
& MAP_ANONYMOUS
)) {
221 /* msync() won't work here, so we return an error if write is
222 possible while it is a shared mapping */
223 if ((flags
& MAP_TYPE
) == MAP_SHARED
&&
227 /* adjust protection to be able to read */
228 if (!(prot1
& PROT_WRITE
))
229 mprotect(host_start
, qemu_host_page_size
, prot1
| PROT_WRITE
);
231 /* read the corresponding file data */
232 if (pread(fd
, g2h_untagged(start
), end
- start
, offset
) == -1)
235 /* put final protection */
236 if (prot_new
!= (prot1
| PROT_WRITE
))
237 mprotect(host_start
, qemu_host_page_size
, prot_new
);
239 if (prot_new
!= prot1
) {
240 mprotect(host_start
, qemu_host_page_size
, prot_new
);
242 if (prot_new
& PROT_WRITE
) {
243 memset(g2h_untagged(start
), 0, end
- start
);
249 #if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
250 #ifdef TARGET_AARCH64
251 # define TASK_UNMAPPED_BASE 0x5500000000
253 # define TASK_UNMAPPED_BASE (1ul << 38)
256 # define TASK_UNMAPPED_BASE 0x40000000
258 abi_ulong mmap_next_start
= TASK_UNMAPPED_BASE
;
260 unsigned long last_brk
;
262 /* Subroutine of mmap_find_vma, used when we have pre-allocated a chunk
263 of guest address space. */
264 static abi_ulong
mmap_find_vma_reserved(abi_ulong start
, abi_ulong size
,
267 abi_ulong addr
, end_addr
, incr
= qemu_host_page_size
;
271 if (size
> reserved_va
) {
272 return (abi_ulong
)-1;
275 /* Note that start and size have already been aligned by mmap_find_vma. */
277 end_addr
= start
+ size
;
278 if (start
> reserved_va
- size
) {
279 /* Start at the top of the address space. */
280 end_addr
= ((reserved_va
- size
) & -align
) + size
;
284 /* Search downward from END_ADDR, checking to see if a page is in use. */
288 if (addr
> end_addr
) {
290 /* Failure. The entire address space has been searched. */
291 return (abi_ulong
)-1;
293 /* Re-start at the top of the address space. */
294 addr
= end_addr
= ((reserved_va
- size
) & -align
) + size
;
297 prot
= page_get_flags(addr
);
299 /* Page in use. Restart below this page. */
300 addr
= end_addr
= ((addr
- size
) & -align
) + size
;
301 } else if (addr
&& addr
+ size
== end_addr
) {
302 /* Success! All pages between ADDR and END_ADDR are free. */
303 if (start
== mmap_next_start
) {
304 mmap_next_start
= addr
;
313 * Find and reserve a free memory area of size 'size'. The search
315 * It must be called with mmap_lock() held.
316 * Return -1 if error.
318 abi_ulong
mmap_find_vma(abi_ulong start
, abi_ulong size
, abi_ulong align
)
324 align
= MAX(align
, qemu_host_page_size
);
326 /* If 'start' == 0, then a default start address is used. */
328 start
= mmap_next_start
;
330 start
&= qemu_host_page_mask
;
332 start
= ROUND_UP(start
, align
);
334 size
= HOST_PAGE_ALIGN(size
);
337 return mmap_find_vma_reserved(start
, size
, align
);
341 wrapped
= repeat
= 0;
344 for (;; prev
= ptr
) {
346 * Reserve needed memory area to avoid a race.
347 * It should be discarded using:
348 * - mmap() with MAP_FIXED flag
349 * - mremap() with MREMAP_FIXED flag
350 * - shmat() with SHM_REMAP flag
352 ptr
= mmap(g2h_untagged(addr
), size
, PROT_NONE
,
353 MAP_ANONYMOUS
|MAP_PRIVATE
|MAP_NORESERVE
, -1, 0);
355 /* ENOMEM, if host address space has no memory */
356 if (ptr
== MAP_FAILED
) {
357 return (abi_ulong
)-1;
360 /* Count the number of sequential returns of the same address.
361 This is used to modify the search algorithm below. */
362 repeat
= (ptr
== prev
? repeat
+ 1 : 0);
364 if (h2g_valid(ptr
+ size
- 1)) {
367 if ((addr
& (align
- 1)) == 0) {
369 if (start
== mmap_next_start
&& addr
>= TASK_UNMAPPED_BASE
) {
370 mmap_next_start
= addr
+ size
;
375 /* The address is not properly aligned for the target. */
378 /* Assume the result that the kernel gave us is the
379 first with enough free space, so start again at the
380 next higher target page. */
381 addr
= ROUND_UP(addr
, align
);
384 /* Sometimes the kernel decides to perform the allocation
385 at the top end of memory instead. */
389 /* Start over at low memory. */
393 /* Fail. This unaligned block must the last. */
398 /* Since the result the kernel gave didn't fit, start
399 again at low memory. If any repetition, fail. */
400 addr
= (repeat
? -1 : 0);
403 /* Unmap and try again. */
406 /* ENOMEM if we checked the whole of the target address space. */
407 if (addr
== (abi_ulong
)-1) {
408 return (abi_ulong
)-1;
409 } else if (addr
== 0) {
411 return (abi_ulong
)-1;
414 /* Don't actually use 0 when wrapping, instead indicate
415 that we'd truly like an allocation in low memory. */
416 addr
= (mmap_min_addr
> TARGET_PAGE_SIZE
417 ? TARGET_PAGE_ALIGN(mmap_min_addr
)
419 } else if (wrapped
&& addr
>= start
) {
420 return (abi_ulong
)-1;
425 /* NOTE: all the constants are the HOST ones */
426 abi_long
target_mmap(abi_ulong start
, abi_ulong len
, int target_prot
,
427 int flags
, int fd
, abi_ulong offset
)
429 abi_ulong ret
, end
, real_start
, real_end
, retaddr
, host_offset
, host_len
;
430 int page_flags
, host_prot
;
433 trace_target_mmap(start
, len
, target_prot
, flags
, fd
, offset
);
440 page_flags
= validate_prot_to_pageflags(&host_prot
, target_prot
);
446 /* Also check for overflows... */
447 len
= TARGET_PAGE_ALIGN(len
);
453 if (offset
& ~TARGET_PAGE_MASK
) {
459 * If we're mapping shared memory, ensure we generate code for parallel
460 * execution and flush old translations. This will work up to the level
461 * supported by the host -- anything that requires EXCP_ATOMIC will not
462 * be atomic with respect to an external process.
464 if (flags
& MAP_SHARED
) {
465 CPUState
*cpu
= thread_cpu
;
466 if (!(cpu
->tcg_cflags
& CF_PARALLEL
)) {
467 cpu
->tcg_cflags
|= CF_PARALLEL
;
472 real_start
= start
& qemu_host_page_mask
;
473 host_offset
= offset
& qemu_host_page_mask
;
475 /* If the user is asking for the kernel to find a location, do that
476 before we truncate the length for mapping files below. */
477 if (!(flags
& MAP_FIXED
)) {
478 host_len
= len
+ offset
- host_offset
;
479 host_len
= HOST_PAGE_ALIGN(host_len
);
480 start
= mmap_find_vma(real_start
, host_len
, TARGET_PAGE_SIZE
);
481 if (start
== (abi_ulong
)-1) {
487 /* When mapping files into a memory area larger than the file, accesses
488 to pages beyond the file size will cause a SIGBUS.
490 For example, if mmaping a file of 100 bytes on a host with 4K pages
491 emulating a target with 8K pages, the target expects to be able to
492 access the first 8K. But the host will trap us on any access beyond
495 When emulating a target with a larger page-size than the hosts, we
496 may need to truncate file maps at EOF and add extra anonymous pages
497 up to the targets page boundary. */
499 if ((qemu_real_host_page_size() < qemu_host_page_size
) &&
500 !(flags
& MAP_ANONYMOUS
)) {
503 if (fstat (fd
, &sb
) == -1)
506 /* Are we trying to create a map beyond EOF?. */
507 if (offset
+ len
> sb
.st_size
) {
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 len
= REAL_HOST_PAGE_ALIGN(sb
.st_size
- offset
);
515 if (!(flags
& MAP_FIXED
)) {
516 unsigned long host_start
;
519 host_len
= len
+ offset
- host_offset
;
520 host_len
= HOST_PAGE_ALIGN(host_len
);
522 /* Note: we prefer to control the mapping address. It is
523 especially important if qemu_host_page_size >
524 qemu_real_host_page_size */
525 p
= mmap(g2h_untagged(start
), host_len
, host_prot
,
526 flags
| MAP_FIXED
| MAP_ANONYMOUS
, -1, 0);
527 if (p
== MAP_FAILED
) {
530 /* update start so that it points to the file position at 'offset' */
531 host_start
= (unsigned long)p
;
532 if (!(flags
& MAP_ANONYMOUS
)) {
533 p
= mmap(g2h_untagged(start
), len
, host_prot
,
534 flags
| MAP_FIXED
, fd
, host_offset
);
535 if (p
== MAP_FAILED
) {
536 munmap(g2h_untagged(start
), host_len
);
539 host_start
+= offset
- host_offset
;
541 start
= h2g(host_start
);
543 if (start
& ~TARGET_PAGE_MASK
) {
548 real_end
= HOST_PAGE_ALIGN(end
);
551 * Test if requested memory area fits target address space
552 * It can fail only on 64-bit host with 32-bit target.
553 * On any other target/host host mmap() handles this error correctly.
555 if (end
< start
|| !guest_range_valid_untagged(start
, len
)) {
560 /* worst case: we cannot map the file because the offset is not
561 aligned, so we read it */
562 if (!(flags
& MAP_ANONYMOUS
) &&
563 (offset
& ~qemu_host_page_mask
) != (start
& ~qemu_host_page_mask
)) {
564 /* msync() won't work here, so we return an error if write is
565 possible while it is a shared mapping */
566 if ((flags
& MAP_TYPE
) == MAP_SHARED
&&
567 (host_prot
& PROT_WRITE
)) {
571 retaddr
= target_mmap(start
, len
, target_prot
| PROT_WRITE
,
572 MAP_FIXED
| MAP_PRIVATE
| MAP_ANONYMOUS
,
576 if (pread(fd
, g2h_untagged(start
), len
, offset
) == -1)
578 if (!(host_prot
& PROT_WRITE
)) {
579 ret
= target_mprotect(start
, len
, target_prot
);
585 /* handle the start of the mapping */
586 if (start
> real_start
) {
587 if (real_end
== real_start
+ qemu_host_page_size
) {
588 /* one single host page */
589 ret
= mmap_frag(real_start
, start
, end
,
590 host_prot
, flags
, fd
, offset
);
595 ret
= mmap_frag(real_start
, start
, real_start
+ qemu_host_page_size
,
596 host_prot
, flags
, fd
, offset
);
599 real_start
+= qemu_host_page_size
;
601 /* handle the end of the mapping */
602 if (end
< real_end
) {
603 ret
= mmap_frag(real_end
- qemu_host_page_size
,
604 real_end
- qemu_host_page_size
, end
,
605 host_prot
, flags
, fd
,
606 offset
+ real_end
- qemu_host_page_size
- start
);
609 real_end
-= qemu_host_page_size
;
612 /* map the middle (easier) */
613 if (real_start
< real_end
) {
615 unsigned long offset1
;
616 if (flags
& MAP_ANONYMOUS
)
619 offset1
= offset
+ real_start
- start
;
620 p
= mmap(g2h_untagged(real_start
), real_end
- real_start
,
621 host_prot
, flags
, fd
, offset1
);
627 if (flags
& MAP_ANONYMOUS
) {
628 page_flags
|= PAGE_ANON
;
630 page_flags
|= PAGE_RESET
;
631 page_set_flags(start
, start
+ len
, page_flags
);
633 trace_target_mmap_complete(start
);
634 if (qemu_loglevel_mask(CPU_LOG_PAGE
)) {
635 FILE *f
= qemu_log_trylock();
637 fprintf(f
, "page layout changed following mmap\n");
642 tb_invalidate_phys_range(start
, start
+ len
);
650 static void mmap_reserve(abi_ulong start
, abi_ulong size
)
652 abi_ulong real_start
;
658 real_start
= start
& qemu_host_page_mask
;
659 real_end
= HOST_PAGE_ALIGN(start
+ size
);
661 if (start
> real_start
) {
662 /* handle host page containing start */
664 for (addr
= real_start
; addr
< start
; addr
+= TARGET_PAGE_SIZE
) {
665 prot
|= page_get_flags(addr
);
667 if (real_end
== real_start
+ qemu_host_page_size
) {
668 for (addr
= end
; addr
< real_end
; addr
+= TARGET_PAGE_SIZE
) {
669 prot
|= page_get_flags(addr
);
674 real_start
+= qemu_host_page_size
;
676 if (end
< real_end
) {
678 for (addr
= end
; addr
< real_end
; addr
+= TARGET_PAGE_SIZE
) {
679 prot
|= page_get_flags(addr
);
682 real_end
-= qemu_host_page_size
;
684 if (real_start
!= real_end
) {
685 mmap(g2h_untagged(real_start
), real_end
- real_start
, PROT_NONE
,
686 MAP_FIXED
| MAP_ANONYMOUS
| MAP_PRIVATE
| MAP_NORESERVE
,
691 int target_munmap(abi_ulong start
, abi_ulong len
)
693 abi_ulong end
, real_start
, real_end
, addr
;
696 trace_target_munmap(start
, len
);
698 if (start
& ~TARGET_PAGE_MASK
)
699 return -TARGET_EINVAL
;
700 len
= TARGET_PAGE_ALIGN(len
);
701 if (len
== 0 || !guest_range_valid_untagged(start
, len
)) {
702 return -TARGET_EINVAL
;
707 real_start
= start
& qemu_host_page_mask
;
708 real_end
= HOST_PAGE_ALIGN(end
);
710 if (start
> real_start
) {
711 /* handle host page containing start */
713 for(addr
= real_start
; addr
< start
; addr
+= TARGET_PAGE_SIZE
) {
714 prot
|= page_get_flags(addr
);
716 if (real_end
== real_start
+ qemu_host_page_size
) {
717 for(addr
= end
; addr
< real_end
; addr
+= TARGET_PAGE_SIZE
) {
718 prot
|= page_get_flags(addr
);
723 real_start
+= qemu_host_page_size
;
725 if (end
< real_end
) {
727 for(addr
= end
; addr
< real_end
; addr
+= TARGET_PAGE_SIZE
) {
728 prot
|= page_get_flags(addr
);
731 real_end
-= qemu_host_page_size
;
735 /* unmap what we can */
736 if (real_start
< real_end
) {
738 mmap_reserve(real_start
, real_end
- real_start
);
740 ret
= munmap(g2h_untagged(real_start
), real_end
- real_start
);
745 page_set_flags(start
, start
+ len
, 0);
746 tb_invalidate_phys_range(start
, start
+ len
);
752 abi_long
target_mremap(abi_ulong old_addr
, abi_ulong old_size
,
753 abi_ulong new_size
, unsigned long flags
,
759 if (!guest_range_valid_untagged(old_addr
, old_size
) ||
760 ((flags
& MREMAP_FIXED
) &&
761 !guest_range_valid_untagged(new_addr
, new_size
)) ||
762 ((flags
& MREMAP_MAYMOVE
) == 0 &&
763 !guest_range_valid_untagged(old_addr
, new_size
))) {
770 if (flags
& MREMAP_FIXED
) {
771 host_addr
= mremap(g2h_untagged(old_addr
), old_size
, new_size
,
772 flags
, g2h_untagged(new_addr
));
774 if (reserved_va
&& host_addr
!= MAP_FAILED
) {
775 /* If new and old addresses overlap then the above mremap will
776 already have failed with EINVAL. */
777 mmap_reserve(old_addr
, old_size
);
779 } else if (flags
& MREMAP_MAYMOVE
) {
780 abi_ulong mmap_start
;
782 mmap_start
= mmap_find_vma(0, new_size
, TARGET_PAGE_SIZE
);
784 if (mmap_start
== -1) {
786 host_addr
= MAP_FAILED
;
788 host_addr
= mremap(g2h_untagged(old_addr
), old_size
, new_size
,
789 flags
| MREMAP_FIXED
,
790 g2h_untagged(mmap_start
));
792 mmap_reserve(old_addr
, old_size
);
797 if (reserved_va
&& old_size
< new_size
) {
799 for (addr
= old_addr
+ old_size
;
800 addr
< old_addr
+ new_size
;
802 prot
|= page_get_flags(addr
);
806 host_addr
= mremap(g2h_untagged(old_addr
),
807 old_size
, new_size
, flags
);
809 if (host_addr
!= MAP_FAILED
) {
810 /* Check if address fits target address space */
811 if (!guest_range_valid_untagged(h2g(host_addr
), new_size
)) {
812 /* Revert mremap() changes */
813 host_addr
= mremap(g2h_untagged(old_addr
),
814 new_size
, old_size
, flags
);
816 host_addr
= MAP_FAILED
;
817 } else if (reserved_va
&& old_size
> new_size
) {
818 mmap_reserve(old_addr
+ old_size
, old_size
- new_size
);
823 host_addr
= MAP_FAILED
;
827 if (host_addr
== MAP_FAILED
) {
830 new_addr
= h2g(host_addr
);
831 prot
= page_get_flags(old_addr
);
832 page_set_flags(old_addr
, old_addr
+ old_size
, 0);
833 page_set_flags(new_addr
, new_addr
+ new_size
,
834 prot
| PAGE_VALID
| PAGE_RESET
);
836 tb_invalidate_phys_range(new_addr
, new_addr
+ new_size
);
841 static bool can_passthrough_madv_dontneed(abi_ulong start
, abi_ulong end
)
845 if ((start
| end
) & ~qemu_host_page_mask
) {
849 for (addr
= start
; addr
< end
; addr
+= TARGET_PAGE_SIZE
) {
850 if (!(page_get_flags(addr
) & PAGE_ANON
)) {
858 abi_long
target_madvise(abi_ulong start
, abi_ulong len_in
, int advice
)
863 if (start
& ~TARGET_PAGE_MASK
) {
864 return -TARGET_EINVAL
;
866 len
= TARGET_PAGE_ALIGN(len_in
);
868 if (len_in
&& !len
) {
869 return -TARGET_EINVAL
;
874 return -TARGET_EINVAL
;
881 if (!guest_range_valid_untagged(start
, len
)) {
882 return -TARGET_EINVAL
;
886 * A straight passthrough may not be safe because qemu sometimes turns
887 * private file-backed mappings into anonymous mappings.
889 * This is a hint, so ignoring and returning success is ok.
891 * This breaks MADV_DONTNEED, completely implementing which is quite
892 * complicated. However, there is one low-hanging fruit: host-page-aligned
893 * anonymous mappings. In this case passthrough is safe, so do it.
896 if (advice
== MADV_DONTNEED
&&
897 can_passthrough_madv_dontneed(start
, end
)) {
898 ret
= get_errno(madvise(g2h_untagged(start
), len
, MADV_DONTNEED
));
900 page_reset_target_data(start
, start
+ len
);