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 48f7433dac6f5ac4e76b6a8841b3db0d45c5f19d..d28815325ef027ce1013d3eec241ba9a8a2ff98a 100644 (file)
--- 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