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

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Message-ID: <20141103164539.GA18104@cloud>
Date:	Mon, 3 Nov 2014 08:45:39 -0800
From:	josh@...htriplett.org
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
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 Mon, Nov 03, 2014 at 03:27:48PM +0000, 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.

OK, fair enough.  Do you want the patch series respun to add that select
in patch 10/10, or would you consider it sufficient to add that in a
followup patch, since the kernel will build and boot either way (so it
won't break bisection)?

Related to that: Is it intentional that FB_UVESA doesn't depend on X86,
even though FB_VESA does?  Does v86d run on non-x86 hardware via
emulation?  If so, should FB_UVESA have "select X86_IOPORT if X86"?

- Josh Triplett
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