Re: [PATCH 5/8] x86/vm86: Add a separate config option for hardware IRQ handling

[Ingo Molnar <mingo@kernel.org>]

* Brian Gerst <brgerst@gmail.com> wrote:

> >> Disabling even less-used code that could have system stability impact. We've 
> >> discouraged user-mode drivers for a very long time.  Ironically, other than 
> >> being configured through the vm86 syscall, there isn't really anything 
> >> vm86-specific about it.  All it does is register an IRQ handler that sends a 
> >> signal to the task.
> >
> > So is this actually used by anything? Could we get away with disabling it, 
> > just to see whether anything cares?
> 
> My best guess would be some very old X11 drivers that needed interrupts to run 
> the Video BIOS code.

So let's keep it - but not complicate it with another layer of disabling logic. 
People that rely on legacies will enable vm86 as a single block - they won't 
necessarily know how deeply they rely on it.

What _would_ be useful is to have a 3-mode vm86 sysctl:

   1: enabled
   0: disabled
  -1: disabled permanently (one-shot disabling after bootup)

That way a distro can permanently disable vm86 for a particular bootup by setting 
it to -1 in /etc/sysctl.conf.

The kernel should default that setting to '0'.

Thanks,

	Ingo