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CONFIG_X86_LEGACY_VM86: Legacy VM86 support (obsolete)

General informations

The Linux kernel configuration item CONFIG_X86_LEGACY_VM86 has multiple definitions:

Legacy VM86 support (obsolete) found in arch/x86/Kconfig

The configuration item CONFIG_X86_LEGACY_VM86:

Help text

This option allows user programs to put the CPU into V8086 mode, which is an 80286-era approximation of 16-bit real mode.

Some very old versions of X and/or vbetool require this option for user mode setting. Similarly, DOSEMU will use it if available to accelerate real mode DOS programs. However, any recent version of DOSEMU, X, or vbetool should be fully functional even without kernel VM86 support, as they will all fall back to (pretty well performing) software emulation.

Anything that works on a 64-bit kernel is unlikely to need this option, as 64-bit kernels don't, and can't, support V8086 mode. This option is also unrelated to 16-bit protected mode and is not needed to run most 16-bit programs under Wine.

Enabling this option adds considerable attack surface to the kernel and slows down system calls and exception handling.

Unless you use very old userspace or need the last drop of performance in your real mode DOS games and can't use KVM, say N here.

Legacy VM86 support found in arch/x86/Kconfig

The configuration item CONFIG_X86_LEGACY_VM86:

Help text

This option allows user programs to put the CPU into V8086 mode, which is an 80286-era approximation of 16-bit real mode.

Some very old versions of X and/or vbetool require this option for user mode setting. Similarly, DOSEMU will use it if available to accelerate real mode DOS programs. However, any recent version of DOSEMU, X, or vbetool should be fully functional even without kernel VM86 support, as they will all fall back to software emulation. Nevertheless, if you are using a 16-bit DOS program where 16-bit performance matters, vm86 mode might be faster than emulation and you might want to enable this option.

Note that any app that works on a 64-bit kernel is unlikely to need this option, as 64-bit kernels don't, and can't, support V8086 mode. This option is also unrelated to 16-bit protected mode and is not needed to run most 16-bit programs under Wine.

Enabling this option increases the complexity of the kernel and slows down exception handling a tiny bit.

If unsure, say N here.

Hardware

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