1#!/usr/bin/env python
2#
3# Copyright (C) 2024 The Android Open Source Project
4#
5# Licensed under the Apache License, Version 2.0 (the "License");
6# you may not use this file except in compliance with the License.
7# You may obtain a copy of the License at
8#
9#      http://www.apache.org/licenses/LICENSE-2.0
10#
11# Unless required by applicable law or agreed to in writing, software
12# distributed under the License is distributed on an "AS IS" BASIS,
13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14# See the License for the specific language governing permissions and
15# limitations under the License.
16#
17"""Utils to determine whether to enable UFFD GC."""
18
19import re
20import sys
21
22
23def should_enable_uffd_gc(kernel_version_file):
24  with open(kernel_version_file, 'r') as f:
25    kernel_version = f.read().strip()
26  return should_enable_uffd_gc_impl(kernel_version)
27
28def should_enable_uffd_gc_impl(kernel_version):
29  # See https://source.android.com/docs/core/architecture/kernel/gki-versioning#determine-release
30  p = r"^(?P<w>\d+)[.](?P<x>\d+)[.](?P<y>\d+)(-android(?P<z>\d+)-(?P<k>\d+).*$)?"
31  m = re.match(p, kernel_version)
32  if m is not None:
33    if m.group('z') is not None:
34      android_release = int(m.group('z'))
35      # No need to check w, x, y because all Android 12 kernels have backports.
36      return android_release >= 12
37    else:
38      # Old kernel or non-GKI kernel.
39      version = int(m.group('w'))
40      patch_level = int(m.group('x'))
41      if version < 5:
42        # Old kernel.
43        return False
44      elif (version == 5 and patch_level >= 7) or version >= 6:
45        # New non-GKI kernel. 5.7 supports MREMAP_DONTUNMAP without the need for
46        # backports.
47        return True
48      else:
49        # Non-GKI kernel between 5 and 5.6. It may have backports.
50        raise exit_with_error(kernel_version)
51  elif kernel_version == '<unknown-kernel>':
52    # The kernel information isn't available to the build system, probably
53    # because PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS is set to false. We
54    # assume that the kernel supports UFFD GC because it is the case for most of
55    # the products today and it is the future.
56    return True
57  else:
58    # Unrecognizable non-GKI kernel.
59    raise exit_with_error(kernel_version)
60
61def exit_with_error(kernel_version):
62  sys.exit(f"""
63Unable to determine UFFD GC flag for kernel version "{kernel_version}".
64You can fix this by explicitly setting PRODUCT_ENABLE_UFFD_GC to "true" or
65"false" based on the kernel version.
661. Set PRODUCT_ENABLE_UFFD_GC to "true" if the kernel supports userfaultfd(2)
67   and MREMAP_DONTUNMAP.
682. Set PRODUCT_ENABLE_UFFD_GC to "false" otherwise.""")
69