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x86/vm86: Fix the misleading CONFIG_VM86 Kconfig help text

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The CONFIG_VM86 Kconfig help text is actively misleading, so fix it:

  - Don't mark it 'obsolete' in the text as we'll support the ABI as long as CPUs
    support it.

  - Qualify the part about software emulation and mention that for some apps you
    want a real vm86 mode.

  - Don't scare users away from the option, instead explain what it does.

Reported-by: Stas Sergeev <stsp@list.ru>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar 2015-09-05 08:58:10 +02:00
parent 7c5b190e11
commit 1e6428124f
1 changed files with 12 additions and 11 deletions
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23
arch/x86/Kconfig
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@ -1004,7 +1004,7 @@ config X86_THERMAL_VECTOR
depends on X86_MCE_INTEL
config X86_LEGACY_VM86
bool "Legacy VM86 support (obsolete)"
bool "Legacy VM86 support"
default n
depends on X86_32
---help---
@ -1016,19 +1016,20 @@ config X86_LEGACY_VM86
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.
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.
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.
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 adds considerable attack surface to the
kernel and slows down system calls and exception handling.
Enabling this option increases the complexity of the kernel
and slows down exception handling a tiny bit.
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.
If unsure, say N here.
config VM86
bool