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 <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>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 48f7433..d288153 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1004,7 +1004,7 @@
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 @@
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