xref: /linux/arch/um/Kconfig (revision 52338415) 
1# SPDX-License-Identifier: GPL-2.0
2
3menu "UML-specific options"
4
5config UML
6	bool
7	default y
8	select ARCH_HAS_KCOV
9	select ARCH_NO_PREEMPT
10	select HAVE_ARCH_AUDITSYSCALL
11	select HAVE_ARCH_SECCOMP_FILTER
12	select HAVE_ASM_MODVERSIONS
13	select HAVE_UID16
14	select HAVE_FUTEX_CMPXCHG if FUTEX
15	select HAVE_DEBUG_KMEMLEAK
16	select HAVE_DEBUG_BUGVERBOSE
17	select GENERIC_IRQ_SHOW
18	select GENERIC_CPU_DEVICES
19	select GENERIC_CLOCKEVENTS
20	select HAVE_GCC_PLUGINS
21	select TTY # Needed for line.c
22
23config MMU
24	bool
25	default y
26
27config NO_IOMEM
28	def_bool y
29
30config ISA
31	bool
32
33config SBUS
34	bool
35
36config TRACE_IRQFLAGS_SUPPORT
37	bool
38	default y
39
40config LOCKDEP_SUPPORT
41	bool
42	default y
43
44config STACKTRACE_SUPPORT
45	bool
46	default y
47	select STACKTRACE
48
49config GENERIC_CALIBRATE_DELAY
50	bool
51	default y
52
53config HZ
54	int
55	default 100
56
57config NR_CPUS
58	int
59	range 1 1
60	default 1
61
62source "arch/$(HEADER_ARCH)/um/Kconfig"
63
64config STATIC_LINK
65	bool "Force a static link"
66	default n
67	help
68	  This option gives you the ability to force a static link of UML.
69	  Normally, UML is linked as a shared binary.  This is inconvenient for
70	  use in a chroot jail.  So, if you intend to run UML inside a chroot,
71	  you probably want to say Y here.
72	  Additionally, this option enables using higher memory spaces (up to
73	  2.75G) for UML.
74
75config LD_SCRIPT_STATIC
76	bool
77	default y
78	depends on STATIC_LINK
79
80config LD_SCRIPT_DYN
81	bool
82	default y
83	depends on !LD_SCRIPT_STATIC
84	select MODULE_REL_CRCS if MODVERSIONS
85
86config HOSTFS
87	tristate "Host filesystem"
88	help
89	  While the User-Mode Linux port uses its own root file system for
90	  booting and normal file access, this module lets the UML user
91	  access files stored on the host.  It does not require any
92	  network connection between the Host and UML.  An example use of
93	  this might be:
94
95	  mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
96
97	  where /tmp/fromhost is an empty directory inside UML and
98	  /tmp/umlshare is a directory on the host with files the UML user
99	  wishes to access.
100
101	  For more information, see
102	  <http://user-mode-linux.sourceforge.net/hostfs.html>.
103
104	  If you'd like to be able to work with files stored on the host,
105	  say Y or M here; otherwise say N.
106
107config MCONSOLE
108	bool "Management console"
109	depends on PROC_FS
110	default y
111	help
112	  The user mode linux management console is a low-level interface to
113	  the kernel, somewhat like the i386 SysRq interface.  Since there is
114	  a full-blown operating system running under every user mode linux
115	  instance, there is much greater flexibility possible than with the
116	  SysRq mechanism.
117
118	  If you answer 'Y' to this option, to use this feature, you need the
119	  mconsole client (called uml_mconsole) which is present in CVS in
120	  2.4.5-9um and later (path /tools/mconsole), and is also in the
121	  distribution RPM package in 2.4.6 and later.
122
123	  It is safe to say 'Y' here.
124
125config MAGIC_SYSRQ
126	bool "Magic SysRq key"
127	depends on MCONSOLE
128	help
129	  If you say Y here, you will have some control over the system even
130	  if the system crashes for example during kernel debugging (e.g., you
131	  will be able to flush the buffer cache to disk, reboot the system
132	  immediately or dump some status information). A key for each of the
133	  possible requests is provided.
134
135	  This is the feature normally accomplished by pressing a key
136	  while holding SysRq (Alt+PrintScreen).
137
138	  On UML, this is accomplished by sending a "sysrq" command with
139	  mconsole, followed by the letter for the requested command.
140
141	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
142	  unless you really know what this hack does.
143
144config KERNEL_STACK_ORDER
145	int "Kernel stack size order"
146	default 2 if 64BIT
147	range 2 10 if 64BIT
148	default 1 if !64BIT
149	help
150	  This option determines the size of UML kernel stacks.  They will
151	  be 1 << order pages.  The default is OK unless you're running Valgrind
152	  on UML, in which case, set this to 3.
153	  It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
154	  older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
155	  increase in the size of the state which needs to be saved when handling
156          signals.
157
158config MMAPPER
159	tristate "iomem emulation driver"
160	help
161	  This driver allows a host file to be used as emulated IO memory inside
162	  UML.
163
164config NO_DMA
165	def_bool y
166
167config PGTABLE_LEVELS
168	int
169	default 3 if 3_LEVEL_PGTABLES
170	default 2
171
172config SECCOMP
173	def_bool y
174	prompt "Enable seccomp to safely compute untrusted bytecode"
175	---help---
176	  This kernel feature is useful for number crunching applications
177	  that may need to compute untrusted bytecode during their
178	  execution. By using pipes or other transports made available to
179	  the process as file descriptors supporting the read/write
180	  syscalls, it's possible to isolate those applications in
181	  their own address space using seccomp. Once seccomp is
182	  enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
183	  and the task is only allowed to execute a few safe syscalls
184	  defined by each seccomp mode.
185
186	  If unsure, say Y.
187
188config UML_TIME_TRAVEL_SUPPORT
189	bool
190	prompt "Support time-travel mode (e.g. for test execution)"
191	help
192	  Enable this option to support time travel inside the UML instance.
193
194	  After enabling this option, two modes are accessible at runtime
195	  (selected by the kernel command line), see the kernel's command-
196	  line help for more details.
197
198	  It is safe to say Y, but you probably don't need this.
199
200endmenu
201
202source "arch/um/drivers/Kconfig"
203