On Fri, Jul 18, 2025 at 03:17:00PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 18, 2025 at 02:51:08PM +0300, Yonatan Maman wrote:
> > +++ b/include/linux/memremap.h
> > @@ -89,6 +89,14 @@ struct dev_pagemap_ops {
> > */
> > vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
> >
> > + /*
> > + * Used for private (un-addressable) device memory only. Return a
> > + * corresponding PFN for a page that can be mapped to device
> > + * (e.g using dma_map_page)
> > + */
> > + int (*get_dma_pfn_for_device)(struct page *private_page,
> > + unsigned long *dma_pfn);
>
> This makes no sense. If a page is addressable then it has a PFN.
> If a page is not addressable then it doesn't have a PFN.
The DEVICE_PRIVATE pages have a PFN, but it is not usable for
anything.
This is effectively converting from a DEVICE_PRIVATE page to an actual
DMA'able address of some kind. The DEVICE_PRIVATE is just a non-usable
proxy, like a swap entry, for where the real data is sitting.
Jason
