linux-kernel - Re: [PATCH v6 07/18] iommu: Implement reserved

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Date:   Sun, 8 Jan 2017 17:26:53 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     eric.auger.pro@...il.com, christoffer.dall@...aro.org,
        marc.zyngier@....com, robin.murphy@....com,
        alex.williamson@...hat.com, will.deacon@....com,
        tglx@...utronix.de, jason@...edaemon.net,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        drjones@...hat.com, linux-kernel@...r.kernel.org,
        pranav.sawargaonkar@...il.com, iommu@...ts.linux-foundation.org,
        punit.agrawal@....com, diana.craciun@....com, gpkulkarni@...il.com,
        shankerd@...eaurora.org, bharat.bhushan@....com,
        geethasowjanya.akula@...il.com
Subject: Re: [PATCH v6 07/18] iommu: Implement reserved_regions iommu-group
 sysfs file

Hi,

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
> 
> Thanks
> 
> Eric
>>
>>
>> 	Joerg
>>