arch/um/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2
   3 menu "UML-specific options"
   4
   5 config 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_UID16
  13         select HAVE_FUTEX_CMPXCHG if FUTEX
  14         select HAVE_DEBUG_KMEMLEAK
  15         select HAVE_DEBUG_BUGVERBOSE
  16         select HAVE_COPY_THREAD_TLS
  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
  23 config MMU
  24         bool
  25         default y
  26
  27 config NO_IOMEM
  28         def_bool y
  29
  30 config ISA
  31         bool
  32
  33 config SBUS
  34         bool
  35
  36 config TRACE_IRQFLAGS_SUPPORT
  37         bool
  38         default y
  39
  40 config LOCKDEP_SUPPORT
  41         bool
  42         default y
  43
  44 config STACKTRACE_SUPPORT
  45         bool
  46         default y
  47         select STACKTRACE
  48
  49 config GENERIC_CALIBRATE_DELAY
  50         bool
  51         default y
  52
  53 config HZ
  54         int
  55         default 100
  56
  57 config NR_CPUS
  58         int
  59         range 1 1
  60         default 1
  61
  62 source "arch/$(HEADER_ARCH)/um/Kconfig"
  63
  64 config 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
  75 config LD_SCRIPT_STATIC
  76         bool
  77         default y
  78         depends on STATIC_LINK
  79
  80 config LD_SCRIPT_DYN
  81         bool
  82         default y
  83         depends on !LD_SCRIPT_STATIC
  84         select MODULE_REL_CRCS if MODVERSIONS
  85
  86 config 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
 107 config 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
 125 config 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
 144 config 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
 158 config 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
 164 config NO_DMA
 165         def_bool y
 166
 167 config PGTABLE_LEVELS
 168         int
 169         default 3 if 3_LEVEL_PGTABLES
 170         default 2
 171
 172 config 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
 188 config 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
 200 endmenu
 201
 202 source "arch/um/drivers/Kconfig"