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Date:   Sun, 8 Jan 2017 17:26:53 +0100
From:   Auger Eric <>
To:     Joerg Roedel <>
Subject: Re: [PATCH v6 07/18] iommu: Implement reserved_regions iommu-group
 sysfs file


On 06/01/2017 18:18, Auger Eric wrote:
> Hi Joerg, Robin,
> On 06/01/2017 13:48, Joerg Roedel wrote:
>> On Fri, Jan 06, 2017 at 12:46:05PM +0100, Auger Eric wrote:
>>> On 06/01/2017 12:00, Joerg Roedel wrote:
>>>> I think it also makes sense to report the type of the reserved region.
>>> What is the best practice in that case? Shall we put the type enum
>>> values as strings such as:
>>> - direct
>>> - nomap
>>> - msi
>>> and document that in Documentation/ABI/testing/sysfs-kernel-iommu_groups
>> Yes, a string would be good. An probably 'reserved' is a better name
>> than nomap?
> the iommu_insert_resv_region() function that builds the group reserved
> region list sorts all regions and handles the case where there is an
> overlap between regions. Current code does not care about the type of
> regions. So in case a NOMAP region overlaps with a direct-mapped region,
> what is reported to the user space is the superset and the type depends
> on the overlap. This was suggested by Robin at some point to handle
> overlaps.
> I guess I should merge regions only in case the types equal?
> I remember that Alex thought that user-space should not care so much
> about the type of the regions so I tought it was better for the
> user-space to have a minimal view of the regions.
> On the other hand, this issue of merging regions of different types
> should not happen often but I prefer to highlight the potential issue.

> What is your guidance?

Please forget the question. From an API point of view It does not make
sense that iommu_insert_resv_region() merges regions of a different
types since the type field becomes unreliable. I will fix this.


> Thanks
> Eric
>> 	Joerg

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