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

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Message-ID: <20200929060307.GA6564@infradead.org>
Date:   Tue, 29 Sep 2020 07:03:07 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Eric Auger <eric.auger@...hat.com>
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

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.

> +		if (geo.aperture_end < ULLONG_MAX && geo.aperture_end != geo.aperture_start) {

Please avoid pointlessly overlong lines.