linux-kernel - Re: [RFC 2/3] iommu: Account for dma_mask and iommu aperture in IOVA reserved regions

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Date:   Tue, 29 Sep 2020 09:20:36 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     eric.auger.pro@...il.com, joro@...tes.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        will.deacon@....com, robin.murphy@....com, dwmw2@...radead.org,
        alex.williamson@...hat.com, jean-philippe.brucker@....com
Subject: Re: [RFC 2/3] iommu: Account for dma_mask and iommu aperture in IOVA
 reserved regions

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.
>