xref: /linux/arch/um/Kconfig (revision 846f9e1fb9b9a2c4eecefa2fdbfb51e975a7d532)

# SPDX-License-Identifier: GPL-2.0

menu "UML-specific options"

config UML
	bool
	default y
	select ARCH_HAS_KCOV
	select ARCH_NO_PREEMPT
	select HAVE_ARCH_AUDITSYSCALL
	select HAVE_ARCH_SECCOMP_FILTER
	select HAVE_ASM_MODVERSIONS
	select HAVE_UID16
	select HAVE_FUTEX_CMPXCHG if FUTEX
	select HAVE_DEBUG_KMEMLEAK
	select HAVE_DEBUG_BUGVERBOSE
	select HAVE_COPY_THREAD_TLS
	select NO_DMA
	select GENERIC_IRQ_SHOW
	select GENERIC_CPU_DEVICES
	select GENERIC_CLOCKEVENTS
	select HAVE_GCC_PLUGINS
	select TTY # Needed for line.c

config MMU
	bool
	default y

config NO_IOMEM
	def_bool y

config ISA
	bool

config SBUS
	bool

config TRACE_IRQFLAGS_SUPPORT
	bool
	default y

config LOCKDEP_SUPPORT
	bool
	default y

config STACKTRACE_SUPPORT
	bool
	default y
	select STACKTRACE

config GENERIC_CALIBRATE_DELAY
	bool
	default y

config HZ
	int
	default 100

config NR_CPUS
	int
	range 1 1
	default 1

source "arch/$(HEADER_ARCH)/um/Kconfig"

config FORBID_STATIC_LINK
	bool

config STATIC_LINK
	bool "Force a static link"
	depends on !FORBID_STATIC_LINK
	help
	  This option gives you the ability to force a static link of UML.
	  Normally, UML is linked as a shared binary.  This is inconvenient for
	  use in a chroot jail.  So, if you intend to run UML inside a chroot,
	  you probably want to say Y here.
	  Additionally, this option enables using higher memory spaces (up to
	  2.75G) for UML.

	  NOTE: This option is incompatible with some networking features which
	  depend on features that require being dynamically loaded (like NSS).

config LD_SCRIPT_STATIC
	bool
	default y
	depends on STATIC_LINK

config LD_SCRIPT_DYN
	bool
	default y
	depends on !LD_SCRIPT_STATIC
	select MODULE_REL_CRCS if MODVERSIONS

config HOSTFS
	tristate "Host filesystem"
	help
	  While the User-Mode Linux port uses its own root file system for
	  booting and normal file access, this module lets the UML user
	  access files stored on the host.  It does not require any
	  network connection between the Host and UML.  An example use of
	  this might be:

	  mount none /tmp/fromhost -t hostfs -o /tmp/umlshare

	  where /tmp/fromhost is an empty directory inside UML and
	  /tmp/umlshare is a directory on the host with files the UML user
	  wishes to access.

	  For more information, see
	  <http://user-mode-linux.sourceforge.net/hostfs.html>.

	  If you'd like to be able to work with files stored on the host,
	  say Y or M here; otherwise say N.

config MCONSOLE
	bool "Management console"
	depends on PROC_FS
	default y
	help
	  The user mode linux management console is a low-level interface to
	  the kernel, somewhat like the i386 SysRq interface.  Since there is
	  a full-blown operating system running under every user mode linux
	  instance, there is much greater flexibility possible than with the
	  SysRq mechanism.

	  If you answer 'Y' to this option, to use this feature, you need the
	  mconsole client (called uml_mconsole) which is present in CVS in
	  2.4.5-9um and later (path /tools/mconsole), and is also in the
	  distribution RPM package in 2.4.6 and later.

	  It is safe to say 'Y' here.

config MAGIC_SYSRQ
	bool "Magic SysRq key"
	depends on MCONSOLE
	help
	  If you say Y here, you will have some control over the system even
	  if the system crashes for example during kernel debugging (e.g., you
	  will be able to flush the buffer cache to disk, reboot the system
	  immediately or dump some status information). A key for each of the
	  possible requests is provided.

	  This is the feature normally accomplished by pressing a key
	  while holding SysRq (Alt+PrintScreen).

	  On UML, this is accomplished by sending a "sysrq" command with
	  mconsole, followed by the letter for the requested command.

	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
	  unless you really know what this hack does.

config KERNEL_STACK_ORDER
	int "Kernel stack size order"
	default 2 if 64BIT
	range 2 10 if 64BIT
	default 1 if !64BIT
	help
	  This option determines the size of UML kernel stacks.  They will
	  be 1 << order pages.  The default is OK unless you're running Valgrind
	  on UML, in which case, set this to 3.
	  It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
	  older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
	  increase in the size of the state which needs to be saved when handling
	  signals.

config MMAPPER
	tristate "iomem emulation driver"
	help
	  This driver allows a host file to be used as emulated IO memory inside
	  UML.

config PGTABLE_LEVELS
	int
	default 3 if 3_LEVEL_PGTABLES
	default 2

config SECCOMP
	def_bool y
	prompt "Enable seccomp to safely compute untrusted bytecode"
	help
	  This kernel feature is useful for number crunching applications
	  that may need to compute untrusted bytecode during their
	  execution. By using pipes or other transports made available to
	  the process as file descriptors supporting the read/write
	  syscalls, it's possible to isolate those applications in
	  their own address space using seccomp. Once seccomp is
	  enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
	  and the task is only allowed to execute a few safe syscalls
	  defined by each seccomp mode.

	  If unsure, say Y.

config UML_TIME_TRAVEL_SUPPORT
	bool
	prompt "Support time-travel mode (e.g. for test execution)"
	# inf-cpu mode is incompatible with the benchmarking
	depends on !RAID6_PQ_BENCHMARK
	depends on !SMP
	help
	  Enable this option to support time travel inside the UML instance.

	  After enabling this option, two modes are accessible at runtime
	  (selected by the kernel command line), see the kernel's command-
	  line help for more details.

	  It is safe to say Y, but you probably don't need this.

endmenu

source "arch/um/drivers/Kconfig"