linux-kernel - Re: [PATCH 02/38] Annotate hardware config module parameters in arch/x86/mm/

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Date:   Tue, 18 Apr 2017 13:38:26 +0100
From:   David Howells <dhowells@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org,
        gnomes@...rguk.ukuu.org.uk, gregkh@...uxfoundation.org,
        nouveau@...ts.freedesktop.org, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 02/38] Annotate hardware config module parameters in arch/x86/mm/

Thomas Gleixner <tglx@...utronix.de> wrote:

> > -module_param(mmio_address, ulong, 0);
> > +module_param_hw(mmio_address, ulong, iomem, 0);
> >  MODULE_PARM_DESC(mmio_address, " Start address of the mapping of 16 kB "
> >  				"(or 8 MB if read_far is non-zero).");
> 
> The copied boilerplate above is really nonsensical here. The default
> address is 0, so the init function will emit:
> 
>      pr_err("you have to use the module argument mmio_address.\n");
>      pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!\n");
> 
> Pretty useless when you can't supply a valid address.
> 
>        if (kernel_locked_down()) {
>        		pr_info("This is not allowed because ...");
> 		return -EPERM;
>        }
> 
> would make too much sense for the user, right?

In some drivers, this would be wrong - ipmi, for example - and we've already
been through this.  The hwparam series of patches annotates *all*
ioport/iomem/irq/dma specifiers unconditionally.  The hwparam series is the
way it is is because this has no overhead if it's not used - and also has the
potentially useful side effect of making such parameters greppable.

It may well make sense to add your above suggestion also - but in the other
patch series.

David