From: Andrew Morton <akpm@linux-foundation.org>
To: David Vrabel <david.vrabel@citrix.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 1/2] mm: provide a find_special_page vma operation
Date: Thu, 22 Jan 2015 16:06:20 -0800 [thread overview]
Message-ID: <20150122160620.e5e3f98ad58020832d899352@linux-foundation.org> (raw)
In-Reply-To: <1421682443-20509-2-git-send-email-david.vrabel@citrix.com>
On Mon, 19 Jan 2015 15:47:22 +0000 David Vrabel <david.vrabel@citrix.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@linux-foundation.org>
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next prev parent reply other threads:[~2015-01-23 0:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-19 15:47 [PATCHv3 0/2] mm: infrastructure for correctly handling foreign pages on Xen David Vrabel
2015-01-19 15:47 ` [PATCH 1/2] mm: provide a find_special_page vma operation David Vrabel
2015-01-23 0:06 ` Andrew Morton [this message]
2015-01-19 15:47 ` [PATCH 2/2] mm: add 'foreign' alias for the 'pinned' page flag David Vrabel
2015-01-23 0:06 ` Andrew Morton
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