From 1e6428124fe22906be0de1622c8fed8e50e5de05 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sat, 5 Sep 2015 08:58:10 +0200 Subject: [PATCH] x86/vm86: Fix the misleading CONFIG_VM86 Kconfig help text 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 Cc: Andy Lutomirski Cc: Arjan van de Ven Cc: Austin S Hemmelgarn Cc: Borislav Petkov Cc: Brian Gerst Cc: Josh Boyer Cc: Kees Cook Cc: Linus Torvalds Cc: Matthew Garrett Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- arch/x86/Kconfig | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 48f7433dac6f..d28815325ef0 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -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