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From:   Christoph Hellwig <hch@infradead.org>
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Subject: Re: [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported
 through dma-buf
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On Tue, Sep 06, 2022 at 12:38:44PM +0200, Christian König wrote:
> The problem is once more that this is MMIO space, in other words register
> BARs which needs to be exported/imported.

Everything used for P2P is bar space.

> Adding struct pages for it generally sounds like the wrong approach here.
> You can't even access this with the CPU or would trigger potentially
> unwanted hardware actions.

How would an access from the CPU vs anther device make any difference?

> Would you mind if I start to tackle this problem?

Yes, I've been waiting forever for someone to tacke how the scatterlist
is abused in dma-buf..