linux-kernel - Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID

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Message-ID: <20211018174226.GP2744544@nvidia.com>
Date:   Mon, 18 Oct 2021 14:42:26 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     Liu Yi L <yi.l.liu@...el.com>, alex.williamson@...hat.com,
        hch@....de, jasowang@...hat.com, joro@...tes.org,
        jean-philippe@...aro.org, kevin.tian@...el.com, parav@...lanox.com,
        lkml@...ux.net, pbonzini@...hat.com, lushenming@...wei.com,
        eric.auger@...hat.com, corbet@....net, ashok.raj@...el.com,
        yi.l.liu@...ux.intel.com, jun.j.tian@...el.com, hao.wu@...el.com,
        dave.jiang@...el.com, jacob.jun.pan@...ux.intel.com,
        kwankhede@...dia.com, robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        nicolinc@...dia.com
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

On Mon, Oct 18, 2021 at 02:50:54PM +1100, David Gibson wrote:

> Hrm... which makes me think... if we allow this for the common
> kernel-managed case, do we even need to have capcity in the high-level
> interface for reporting IO holes?  If the kernel can choose a non-zero
> base, it could just choose on x86 to place it's advertised window
> above the IO hole.

If the high level interface is like dma_map() then, no it doesn't need
the ability to report holes. Kernel would find and return the IOVA
from dma_map not accept it in.

Since dma_map is a well proven model I'm inclined to model the
simplied interface after it..

That said, if we have some ioctl 'query iova ranges' I would expect it
to work on an IOAS created by the simplified interface too.

Jason