linux-kernel - Re: [PATCH 7/7] iommu: Add iommu_domain::domain

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Message-ID: <20220124175542.GA987164@nvidia.com>
Date:   Mon, 24 Jan 2022 13:55:42 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops

On Mon, Jan 24, 2022 at 03:11:02PM +0800, Lu Baolu wrote:
> -	int (*enable_nesting)(struct iommu_domain *domain);

Perhaps for another series, but enable_nesting looks like dead code
too, AFAICT.

Or at the very least I can't figure how out VFIO_TYPE1_NESTING_IOMMU
is supposed to work, or find any implementation of it in userspace.

8 years after it was merged in commit f5c9ecebaf2a ("vfio/iommu_type1:
add new VFIO_TYPE1_NESTING_IOMMU IOMMU type")

The commit comment says 'which are nested with the existing
translation installed by VFIO.' but it doesn't explain how the newly
created domain knows what its parent nest is..

Lu, there is an implementation in the Intel driver here, is it usable
at all?

Jason