linux-kernel - Re: DMA-API attr - DMA_ATTR_NO_KERNEL

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Message-ID: <20190626175131.GA17250@infradead.org>
Date:   Wed, 26 Jun 2019 10:51:31 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Pankaj Suryawanshi <pankajssuryawanshi@...il.com>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        iommu@...ts.linux-foundation.org
Subject: Re: DMA-API attr - DMA_ATTR_NO_KERNEL_MAPPING

On Wed, Jun 26, 2019 at 10:12:45PM +0530, Pankaj Suryawanshi wrote:
> [CC: linux kernel and Vlastimil Babka]

The right list is the list for the DMA mapping subsystem, which is
iommu@...ts.linux-foundation.org.  I've also added that.

> > I am writing driver in which I used DMA_ATTR_NO_KERNEL_MAPPING attribute
> > for cma allocation using dma_alloc_attr(), as per kernel docs
> > https://www.kernel.org/doc/Documentation/DMA-attributes.txt  buffers
> > allocated with this attribute can be only passed to user space by calling
> > dma_mmap_attrs().
> >
> > how can I mapped in kernel space (after dma_alloc_attr with
> > DMA_ATTR_NO_KERNEL_MAPPING ) ?

You can't.  And that is the whole point of that API.