Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 7 Nov 2019 11:27:56 +0100
From:   Willy Tarreau <w@1wt.eu>
To:     hpa@zytor.com
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Stephen Hemminger <stephen@networkplumber.org>,
        Juergen Gross <jgross@suse.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage
 further
Message-ID: <20191107102756.GD15536@1wt.eu>
References: <20191106193459.581614484@linutronix.de>
 <20191106202806.241007755@linutronix.de>
 <CAHk-=wjXcS--G3Wd8ZGEOdCNRAWPaUneyN1ryShQL-_yi1kvOA@mail.gmail.com>
 <20191107082541.GF30739@gmail.com>
 <20191107091704.GA15536@1wt.eu>
 <alpine.DEB.2.21.1911071058260.4256@nanos.tec.linutronix.de>
 <71DE81AC-3AD4-47B3-9CBA-A2C7841A3370@zytor.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <71DE81AC-3AD4-47B3-9CBA-A2C7841A3370@zytor.com>
User-Agent: Mutt/1.6.1 (2016-04-27)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 07, 2019 at 02:19:19AM -0800, hpa@zytor.com wrote:
> >Changing ioperm(single port, port range) to be ioperm(all) is going to
> >break a bunch of test cases which actually check whether the permission
> >is restricted to a single I/O port or the requested port range.
> >
> >Thanks,
> >
> >	tglx
> 
> This seems very undesirable... as much as we might wish otherwise, the port
> bitmap is the equivalent to the MMU, and there are definitely users doing
> direct device I/O out there.

Doing these, sure, but doing these while ranges are really checked ?
I mean, the MMU grants you access to the pages you were assigned. Here
with the I/O bitmap you just have to ask for access to port X and you
get it. I could understand the benefit if we had EBUSY in return but
that's not the case, you can actually request access to a port range
another device driver or process is currently using, and mess up with
what it does even by accident. I remember streaming 1-bit music in
userland from the LED of my floppy drive in the late-90s, it used to
cause some trouble to the floppy driver when using mtools in parallel :-)

Willy