On Mon, 19 Jan 2015 15:47:22 +0000 David Vrabel <[email protected]> wrote:
> The optional find_special_page VMA operation is used to lookup the > pages backing a VMA. This is useful in cases where the normal > mechanisms for finding the page don't work. This is only called if > the PTE is special. > > One use case is a Xen PV guest mapping foreign pages into userspace. > > In a Xen PV guest, the PTEs contain MFNs so get_user_pages() (for > example) must do an MFN to PFN (M2P) lookup before it can get the > page. For foreign pages (those owned by another guest) the M2P lookup > returns the PFN as seen by the foreign guest (which would be > completely the wrong page for the local guest). > > This cannot be fixed up improving the M2P lookup since one MFN may be > mapped onto two or more pages so getting the right page is impossible > given just the MFN. Acked-by: Andrew Morton <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
