linux-kernel - Re: [PATCH 4/4] dmaengine: idxd: Use DMA API for in-kernel DMA with PASID

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Date:   Wed, 8 Dec 2021 11:55:16 -0800
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>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Barry Song <21cnbao@...il.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 4/4] dmaengine: idxd: Use DMA API for in-kernel DMA with
 PASID

Hi Jason,

On Wed, 8 Dec 2021 09:13:58 -0400, Jason Gunthorpe <jgg@...dia.com> wrote:

> > This patch utilizes iommu_enable_pasid_dma() to enable DSA to perform
> > DMA requests with PASID under the same mapping managed by DMA mapping
> > API. In addition, SVA-related bits for kernel DMA are removed. As a
> > result, DSA users shall use DMA mapping API to obtain DMA handles
> > instead of using kernel virtual addresses.  
> 
> Er, shouldn't this be adding dma_map/etc type calls?
> 
> You can't really say a driver is using the DMA API without actually
> calling the DMA API..
The IDXD driver is not aware of addressing mode, it is up to the user of
dmaengine API to prepare the buffer mappings. Here we only set up the PASID
such that it can be picked up during DMA work submission. I tested with
/drivers/dma/dmatest.c which does dma_map_page(), map_single etc. also
tested with other pieces under development.

Thanks,

Jacob