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

[Joerg Roedel]

[ 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@xxxxxxxxxx> 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.

Then in the next cycle I will review again more closely what information
about VT-d and AMD-Vi is revealed there and will probably apply what I
can live with.

Thanks,

	Joerg