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 08:10:51 -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 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.

--
Brian Gerst
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