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1 | /* |
2 | * Support for RAM backed by mmaped host memory. | |
3 | * | |
4 | * Copyright (c) 2015 Red Hat, Inc. | |
5 | * | |
6 | * Authors: | |
7 | * Michael S. Tsirkin <mst@redhat.com> | |
8 | * | |
9 | * This work is licensed under the terms of the GNU GPL, version 2 or | |
10 | * later. See the COPYING file in the top-level directory. | |
11 | */ | |
12 | #include <qemu/mmap-alloc.h> | |
13 | #include <sys/types.h> | |
14 | #include <sys/mman.h> | |
15 | #include <assert.h> | |
16 | ||
17 | void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) | |
18 | { | |
19 | /* | |
20 | * Note: this always allocates at least one extra page of virtual address | |
21 | * space, even if size is already aligned. | |
22 | */ | |
23 | size_t total = size + align; | |
24 | void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); | |
25 | size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; | |
26 | void *ptr1; | |
27 | ||
28 | if (ptr == MAP_FAILED) { | |
9d4ec937 | 29 | return MAP_FAILED; |
794e8f30 MT |
30 | } |
31 | ||
32 | /* Make sure align is a power of 2 */ | |
33 | assert(!(align & (align - 1))); | |
34 | /* Always align to host page size */ | |
35 | assert(align >= getpagesize()); | |
36 | ||
37 | ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE, | |
38 | MAP_FIXED | | |
39 | (fd == -1 ? MAP_ANONYMOUS : 0) | | |
40 | (shared ? MAP_SHARED : MAP_PRIVATE), | |
41 | fd, 0); | |
42 | if (ptr1 == MAP_FAILED) { | |
43 | munmap(ptr, total); | |
9d4ec937 | 44 | return MAP_FAILED; |
794e8f30 MT |
45 | } |
46 | ||
47 | ptr += offset; | |
48 | total -= offset; | |
49 | ||
50 | if (offset > 0) { | |
51 | munmap(ptr - offset, offset); | |
52 | } | |
53 | ||
54 | /* | |
55 | * Leave a single PROT_NONE page allocated after the RAM block, to serve as | |
56 | * a guard page guarding against potential buffer overflows. | |
57 | */ | |
58 | if (total > size + getpagesize()) { | |
59 | munmap(ptr + size + getpagesize(), total - size - getpagesize()); | |
60 | } | |
61 | ||
62 | return ptr; | |
63 | } | |
64 | ||
65 | void qemu_ram_munmap(void *ptr, size_t size) | |
66 | { | |
67 | if (ptr) { | |
68 | /* Unmap both the RAM block and the guard page */ | |
69 | munmap(ptr, size + getpagesize()); | |
70 | } | |
71 | } |