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

From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	dmaengine@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Christoph Hellwig <hch@infradead.org>,
	vkoul@kernel.org, robin.murphy@arm.com, will@kernel.org,
	Yi Liu <yi.l.liu@intel.com>, Dave Jiang <dave.jiang@intel.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	Eric Auger <eric.auger@redhat.com>,
	jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API
Date: Tue, 24 May 2022 08:17:27 -0700	[thread overview]
Message-ID: <20220524081727.19c2dd6d@jacob-builder> (raw)
In-Reply-To: <20220524135034.GU1343366@nvidia.com>

Hi Jason,

On Tue, 24 May 2022 10:50:34 -0300, Jason Gunthorpe <jgg@nvidia.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