linux-kernel - Re: [PATCH v7 0/5] Add Intel IOMMU debugfs support

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Date:   Thu, 29 Mar 2018 10:52:15 -0500
From:   Gary R Hook <gary.hook@....com>
To:     Joerg Roedel <joro@...tes.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Gayatri Kammela <gayatri.kammela@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v7 0/5] Add Intel IOMMU debugfs support

On 03/29/2018 03:48 AM, Joerg Roedel wrote:
> [ Adding Gary from AMD to Cc ]
> 
> On Mon, Mar 19, 2018 at 09:37:14AM -0700, Jacob Pan wrote:
>> On Thu, 15 Mar 2018 14:18:54 +0100
>> Joerg Roedel <joro@...tes.org> wrote:
>>
>>> On Thu, Feb 15, 2018 at 08:38:11AM -0800, Jacob Pan wrote:
>>>> Just wondering if your concern is on the implementation or the
>>>> debugfs idea in general. Perhaps have some common IOMMU debugfs?
>>>
>>> My concern mainly is that we add interfaces which reveal
>>> potentially security relevant information
>> I don;t think security is any worse than existing kernel page table in
>> debugfs. i.e. /sys/kernel/debug/page_tables
>> This is a debug feature.
> 
> Okay, so here is the way to go: Please introduce a basic debugfs
> facility to the core iommu code. It should basically only create a
> 'iommu/' directory in debugfs where drivers can create their own
> sub-directories. This must be enabled by a new kconfig option
> (CONFIG_IOMMU_DEBUGFS) and the kernel should print a big fat warning at
> boot when it is enabled. This hopefully prevents anyone from enabling it
> for production kernels.

I'm halfway through this. Where would you like to place the invocation 
of the initialization function?

There's an iommu_init() in iommu.c, But it's a core_initcall, which 
doesn't seem like a good spot. Not knowing enough about bring-up here, 
Would adding another __init function be suitable?

Gary