linux-kernel - Re: [PATCH v6 03/12] iommu: Add attach/detach_dev

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Message-ID: <20220510140238.GD49344@nvidia.com>
Date:   Tue, 10 May 2022 11:02:38 -0300
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>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v6 03/12] iommu: Add attach/detach_dev_pasid domain ops

On Tue, May 10, 2022 at 02:17:29PM +0800, Lu Baolu wrote:

> This adds a pair of common domain ops for this purpose and adds helpers
> to attach/detach a domain to/from a {device, PASID}. 

I wonder if this should not have a detach op - after discussing with
Robin we can see that detach_dev is not used in updated
drivers. Instead attach_dev acts as 'set_domain'

So, it would be more symmetrical if attaching a blocking_domain to the
PASID was the way to 'detach'.

This could be made straightforward by following the sketch I showed to
have a static, global blocing_domain and providing a pointer to it in
struct iommu_ops

Then 'detach pasid' is:

iommu_ops->blocking_domain->ops->attach_dev_pasid(domain, dev, pasid);

And we move away from the notion of 'detach' and in the direction that
everything continuously has a domain set. PASID would logically
default to blocking_domain, though we wouldn't track this anywhere.

Jason