linux-kernel - Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA

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Message-ID: <20211007113221.GF2744544@nvidia.com>
Date:   Thu, 7 Oct 2021 08:32:21 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Barry Song <21cnbao@...il.com>
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        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>, mike.campin@...el.com,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA

On Thu, Oct 07, 2021 at 06:43:33PM +1300, Barry Song wrote:

> So do we have a case where devices can directly access the kernel's data
> structure such as a list/graph/tree with pointers to a kernel virtual address?
> then devices don't need to translate the address of pointers in a structure.
> I assume this is one of the most useful features userspace SVA can provide.

AFIACT that is the only good case for KVA, but it is also completely
against the endianess, word size and DMA portability design of the
kernel.

Going there requires some new set of portable APIs for gobally
coherent KVA dma.

Jason