linux-kernel - Re: [RFC 16/20] vfio/type1: Export symbols for dma [un]map code sharing

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Date:   Tue, 21 Sep 2021 15:14:48 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     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,
        david@...son.dropbear.id.au, nicolinc@...dia.com
Subject: Re: [RFC 16/20] vfio/type1: Export symbols for dma [un]map code
 sharing

On Sun, Sep 19, 2021 at 02:38:44PM +0800, Liu Yi L wrote:
> [HACK. will fix in v2]
> 
> There are two options to impelement vfio type1v2 mapping semantics in
> /dev/iommu.
> 
> One is to duplicate the related code from vfio as the starting point,
> and then merge with vfio type1 at a later time. However vfio_iommu_type1.c
> has over 3000LOC with ~80% related to dma management logic, including:

I can't really see a way forward like this. I think some scheme to
move the vfio datastructure is going to be necessary.

> - the dma map/unmap metadata management
> - page pinning, and related accounting
> - iova range reporting
> - dirty bitmap retrieving
> - dynamic vaddr update, etc.

All of this needs to be part of the iommufd anyhow..

> The alternative is to consolidate type1v2 logic in /dev/iommu immediately,
> which requires converting vfio_iommu_type1 to be a shim driver. 

Another choice is the the datastructure coulde move and the two
drivers could share its code and continue to exist more independently

Jason