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

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Date:   Wed, 11 May 2022 10:32:14 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.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 2022/5/10 22:02, Jason Gunthorpe wrote:
> 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.

I am not sure whether we still need to keep the blocking domain concept
when we are entering the new PASID world. Please allow me to wait and
listen to more opinions.

Best regards,
baolu