linux-kernel - Re: helping with remapping vmem for dma

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Message-ID: <20220615131700.GA18061@lst.de>
Date:   Wed, 15 Jun 2022 15:17:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Frank Wunderlich <frank-w@...lic-files.de>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: helping with remapping vmem for dma

On Wed, Jun 15, 2022 at 02:15:33PM +0100, Robin Murphy wrote:
> Put simply, if you want to call dma_map_single() on a buffer, then that 
> buffer needs to be allocated with kmalloc() (or technically alloc_pages(), 
> but then dma_map_page() would make more sense when dealing with entire 
> pages.

Yes.  It sounds like the memory here comes from the dma coherent
allocator, in which case the code need to use the address returned
by that and not create another mapping.