Re: [PATCH 03/10] accel/ivpu: Add debug prints for MMU map/unmap operations

[Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>]

On 05.01.2024 16:32, Jeffrey Hugo wrote:
> On 1/5/2024 4:22 AM, Jacek Lawrynowicz wrote:
>> From: "Wachowski, Karol" <karol.wachowski@intel.com>
>>
>> It is common need to be able to  see IOVA/physical to VPU addresses
> 
> Errant double space between "to" and "see"

Sure

>> mappings. Especially when debugging different kind of memory related
>> issues. Lack of such logs forces user to modify and recompile KMD manually.
>>
>> This commit adds those logs under MMU debug mask which can be turned on
>> dynamically with module param during KMD load.
> As far as I understand, the preference is to not expose any kind of raw addresses as it is seen as a security issue, and usually the addresses don't have any real value to someone reading logs, etc.  I beleive I picked this up from GregKH.
> 
> However, this commit text suggests there is value, and I see that one needs to be root to enable this which could probably be considered a sufficent gate to avoiding the data getting into the wrong hands.
> 
> Is it possible to provide more details as a justification for this? Perhaps an example of a past issue where this data was necessary for debug?

There were multiple occasions were these messages were useful:
  - Debugging IOMMU issues on pre-production hardware
  - Enabling DevTLB cache on a functional simulator
  - Debugging performance issues with fragmented buffers

There is always some security tradeoff when enabling debug features but in this case it seems to be worth it.