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Subject: Re: [RFC 2/3] iommu: Account for dma_mask and iommu aperture in IOVA
 reserved regions
To:     Christoph Hellwig <hch@infradead.org>
Cc:     eric.auger.pro@gmail.com, joro@8bytes.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        will.deacon@arm.com, robin.murphy@arm.com, dwmw2@infradead.org,
        alex.williamson@redhat.com, jean-philippe.brucker@arm.com
References: <20200928195037.22654-1-eric.auger@redhat.com>
 <20200928195037.22654-3-eric.auger@redhat.com>
 <20200929060307.GA6564@infradead.org>
From:   Auger Eric <eric.auger@redhat.com>
Message-ID: <35b5ff6b-1c6a-ced0-aeb0-6135b9fa26d5@redhat.com>
Date:   Tue, 29 Sep 2020 09:20:36 +0200
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Hi Christoph,

On 9/29/20 8:03 AM, Christoph Hellwig wrote:
> On Mon, Sep 28, 2020 at 09:50:36PM +0200, Eric Auger wrote:
>> VFIO currently exposes the usable IOVA regions through the
>> VFIO_IOMMU_GET_INFO ioctl. However it fails to take into account
>> the dma_mask of the devices within the container. The top limit
>> currently is defined by the iommu aperture.
> 
> Can we take a step back here?  The dma_mask only has a meaning for
> the DMA API, and not the iommu API, it should have no relevance here.
> 
> More importantly if we are using vfio no dma_mask should be set to
> start with.

You will find more context in my reply to Alex.

Thanks

Eric
> 
>> +		if (geo.aperture_end < ULLONG_MAX && geo.aperture_end != geo.aperture_start) {
> 
> Please avoid pointlessly overlong lines.
>