Messages in this thread |  | | Date | Thu, 1 Mar 2018 16:18:18 -0500 | From | Jerome Glisse <> | Subject | Re: [PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory |
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On Thu, Mar 01, 2018 at 02:11:34PM -0700, Logan Gunthorpe wrote: > > > On 01/03/18 02:03 PM, Benjamin Herrenschmidt wrote: > > However, what happens if anything calls page_address() on them ? Some > > DMA ops do that for example, or some devices might ... > > Although we could probably work around it with some pain, we rely on > page_address() and virt_to_phys(), etc to work on these pages. So on x86, > yes, it makes it into the linear mapping.
This is pretty easy to do with HMM:
unsigned long hmm_page_to_phys_pfn(struct page *page) { struct hmm_devmem *devmem; unsigned long ppfn;
/* Sanity test maybe BUG_ON() */ if (!is_device_private_page(page)) return -1UL;
devmem = page->pgmap->data; ppfn = page_to_page(page) - devmem->pfn_first; return ppfn + devmem->device_phys_base_pfn; }
Note that last field does not exist in today HMM because i did not need such helper so far but this can be added.
Cheers, Jérôme
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