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 09:59:17 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
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

On Fri, Jul 31, 2015 at 9:50 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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?

My best guess would be some very old X11 drivers that needed
interrupts to run the Video BIOS code.

--
Brian Gerst
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