linux-kernel - Re: [PATCH v4 10/10] x86: Support compiling out userspace IO (iopl and ioperm)

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Message-ID: <5457D6FF.5060800@amacapital.net>
Date:	Mon, 03 Nov 2014 11:26:55 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Josh Triplett <josh@...htriplett.org>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, x86@...nel.org
Subject: Re: [PATCH v4 10/10] x86: Support compiling out userspace IO (iopl
 and ioperm)

On 11/03/2014 07:27 AM, One Thousand Gnomes wrote:
>>> This isn't unreasonable but there are drivers with userspace helpers that
>>> use iopl/ioperm type functionality where you should be doing a SELECT of
>>> X86_IOPORT. The one that comes to mind is the uvesa driver. From a quick
>>> scan it may these days be the only mainstream one that needs the select
>>> adding.
>>
>> Should kernel drivers really express dependencies that only their
>> (current instances of) corresponding userspace components need?
>> Something seems wrong about that.
> 
> uvesafb will always need X86_IOPORT. It's kind of implicit in the design.
> I'm not suggesting that fbdev should select X86_IOPORT but in the uvesafb
> case at least it's completely useless to have one and not the other.

Are there any users of uvesafb at all?  Last time I changed that driver,
I tried to test it, and I was unable to find a copy of the userspace helper.

--Andy

> 
>> IO_BITMAP_LONGS already gets defined to (0/sizeof(long)).  And as far as
>> I can tell, that would only work for init_tss_io, not anything else.
>> Even then, that would only work with a zero-size array left around in
>> tss_struct, which doesn't seem appropriate.  The remaining ifdefs wrap
>> code that GCC could not constant-fold away, and making that code
>> constant-foldable seems significantly more invasive than the ifdefs.
> 
> OK
> 

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