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Message-Id: <20150122160620.e5e3f98ad58020832d899352@linux-foundation.org> Date: Thu, 22 Jan 2015 16:06:20 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: David Vrabel <david.vrabel@...rix.com> Cc: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org> Subject: Re: [PATCH 1/2] mm: provide a find_special_page vma operation On Mon, 19 Jan 2015 15:47:22 +0000 David Vrabel <david.vrabel@...rix.com> 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 <akpm@...ux-foundation.org> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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