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

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Date:	Fri, 31 Jul 2015 15:50:38 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 5/8] x86/vm86: Add a separate config option for hardware
 IRQ handling


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

> On Fri, Jul 31, 2015 at 4:57 AM, Ingo Molnar <mingo@...nel.org> wrote:
> >
> > * Brian Gerst <brgerst@...il.com> wrote:
> >
> >> Allow disabling hardware interrupt support for vm86.
> >>
> >> Signed-off-by: Brian Gerst <brgerst@...il.com>
> >> ---
> >>  arch/x86/Kconfig                   |  8 ++++++++
> >>  arch/x86/include/asm/irq_vectors.h | 10 ----------
> >>  arch/x86/include/asm/vm86.h        | 20 ++++++++++++++++++--
> >>  arch/x86/kernel/vm86_32.c          | 12 ++++++++++--
> >>  4 files changed, 36 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> >> index cbd2d62..7c7ec31 100644
> >> --- a/arch/x86/Kconfig
> >> +++ b/arch/x86/Kconfig
> >> @@ -1067,6 +1067,14 @@ config VM86
> >>         bool
> >>         default X86_LEGACY_VM86
> >>
> >> +config VM86_INTERRUPTS
> >> +     bool "Enable VM86 interrupt support"
> >> +     default y
> >> +     depends on VM86
> >> +     ---help---
> >> +       This option allows VM86 programs to request interrupts for
> >> +       real mode hardware drivers.
> >
> > So I'm wondering what the justification for this is. People can disable vm86
> > already via CONFIG_X86_LEGACY_VM86. The extra config just uglifies the code
> > unnecessarily.
> >
> > Thanks,
> >
> >         Ingo
> 
> 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?

Thanks,

	Ingo
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