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

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Message-ID: <0858b719-2888-0645-66d2-56fe698f4e2f@redhat.com>
Date:   Fri, 6 Jan 2017 18:18:33 +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 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?

Thanks

Eric
> 
> 
> 	Joerg
>