1 /*
2 * Copyright (C) 2019 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "berberis/base/memfd_backed_mmap.h"
18
19 #include <sys/mman.h>
20 #include <unistd.h>
21
22 #include "berberis/base/fd.h"
23 #include "berberis/base/large_mmap.h"
24 #include "berberis/base/logging.h"
25 #include "berberis/base/mmap.h"
26
27 namespace berberis {
28
29 // Creates memfd region of memfd_file_size bytes filled with value.
CreateAndFillMemfd(const char * name,size_t memfd_file_size,uintptr_t value)30 int CreateAndFillMemfd(const char* name, size_t memfd_file_size, uintptr_t value) {
31 const size_t kPageSize = sysconf(_SC_PAGE_SIZE);
32 CHECK_EQ(memfd_file_size % sizeof(value), 0);
33 CHECK_EQ(memfd_file_size % kPageSize, 0);
34
35 // Use intermediate map to fully initialize file content. It lets compiler
36 // optimize the loop below and limits WriteFully to fd to one call. Running
37 // the Memfd.uintptr_t test on this showed 4x performance improvement.
38 uintptr_t* memfd_file_content = static_cast<uintptr_t*>(MmapOrDie(memfd_file_size));
39
40 for (size_t i = 0; i < memfd_file_size / sizeof(value); ++i) {
41 memfd_file_content[i] = value;
42 }
43
44 int memfd = CreateMemfdOrDie(name);
45
46 WriteFullyOrDie(memfd, memfd_file_content, memfd_file_size);
47
48 MunmapOrDie(memfd_file_content, memfd_file_size);
49
50 return memfd;
51 }
52
53 // Allocates a region of map_size bytes and backs it in chunks with memfd region
54 // of memfd_file_size bytes.
CreateMemfdBackedMapOrDie(int memfd,size_t map_size,size_t memfd_file_size)55 void* CreateMemfdBackedMapOrDie(int memfd, size_t map_size, size_t memfd_file_size) {
56 const size_t kPageSize = sysconf(_SC_PAGE_SIZE);
57 CHECK_EQ(map_size % memfd_file_size, 0);
58 CHECK_EQ(memfd_file_size % kPageSize, 0);
59
60 // Reserving memory for the map. Instruct kernel to not commit any RAM to
61 // the map by using MAP_NORESERVE. It would be a waste anyways since
62 // this region is used to create memfd backed mmaps.
63 uint8_t* ptr = static_cast<uint8_t*>(
64 LargeMmapImplOrDie({.size = map_size, .flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE}));
65
66 // map memfd
67 for (size_t i = 0; i < map_size / memfd_file_size; ++i) {
68 MmapImplOrDie({.addr = ptr + (i * memfd_file_size),
69 .size = memfd_file_size,
70 .flags = MAP_PRIVATE | MAP_FIXED,
71 .fd = memfd});
72 }
73
74 return ptr;
75 }
76
77 } // namespace berberis
78