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Date: Wed, 15 Jan 2025 10:32:34 +0100
From: Christoph Hellwig <hch@lst.de>
To: Jason Gunthorpe <jgg@nvidia.com>, Xu Yilun <yilun.xu@linux.intel.com>,
	Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
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Subject: Re: [RFC PATCH 01/12] dma-buf: Introduce
 dma_buf_get_pfn_unlocked() kAPI
Message-ID: <20250115093234.GB6805@lst.de>
References: <20250108162227.GT5556@nvidia.com> <Z37HpvHAfB0g9OQ-@phenom.ffwll.local> <Z37QaIDUgiygLh74@yilunxu-OptiPlex-7050> <58e97916-e6fd-41ef-84b4-bbf53ed0e8e4@amd.com> <Z38FCOPE7WPprYhx@yilunxu-OptiPlex-7050> <Z4F2X7Fu-5lprLrk@phenom.ffwll.local> <20250110203838.GL5556@nvidia.com> <Z4Z4NKqVG2Vbv98Q@phenom.ffwll.local> <20250114173103.GE5556@nvidia.com> <Z4d4AaLGrhRa5KLJ@phenom.ffwll.local>
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On Wed, Jan 15, 2025 at 09:55:29AM +0100, Simona Vetter wrote:
> I think for 90% of exporters pfn would fit, but there's some really funny
> ones where you cannot get a cpu pfn by design. So we need to keep the
> pfn-less interfaces around. But ideally for the pfn-capable exporters we'd
> have helpers/common code that just implements all the other interfaces.

There is no way to have dma address without a PFN in Linux right now.
How would you generate them?  That implies you have an IOMMU that can
generate IOVAs for something that doesn't have a physical address at
all.

Or do you mean some that don't have pages associated with them, and
thus have pfn_valid fail on them?  They still have a PFN, just not
one that is valid to use in most of the Linux MM.