linux-kernel - Re: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

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Date:   Tue, 24 May 2022 08:17:27 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>, dmaengine@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>, vkoul@...nel.org,
        robin.murphy@....com, will@...nel.org, Yi Liu <yi.l.liu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

Hi Jason,

On Tue, 24 May 2022 10:50:34 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> On Wed, May 18, 2022 at 11:21:15AM -0700, Jacob Pan wrote:
> > DMA requests tagged with PASID can target individual IOMMU domains.
> > Introduce a domain-wide PASID for DMA API, it will be used on the same
> > mapping as legacy DMA without PASID. Let it be IOVA or PA in case of
> > identity domain.  
> 
> Huh? I can't understand what this is trying to say or why this patch
> makes sense.
> 
> We really should not have pasid's like this attached to the domains..
> 
This is the same "DMA API global PASID" you reviewed in v3, I just
singled it out as a standalone patch and renamed it. Here is your previous
review comment.

> +++ b/include/linux/iommu.h
> @@ -105,6 +105,8 @@ struct iommu_domain {
>  	enum iommu_page_response_code (*iopf_handler)(struct iommu_fault *fault,
>  						      void *data);
>  	void *fault_data;
> +	ioasid_t pasid;		/* Used for DMA requests with PASID */
> +	atomic_t pasid_users;  

These are poorly named, this is really the DMA API global PASID and
shouldn't be used for other things.



Perhaps I misunderstood, do you mind explaining more?


Thanks,

Jacob