Re: [Xen-devel] [Hackathon] Linux session notes

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-06-04 at 12:42 +0100, David Vrabel wrote:
> On 04/06/14 12:37, Stefano Stabellini wrote:
> > On Wed, 4 Jun 2014, David Vrabel wrote:
> >> On 04/06/14 12:11, Stefano Stabellini wrote:
> >>> On Mon, 2 Jun 2014, David Vrabel wrote:
> >>>> - Fixing m2p override.  Mapping the same MFN (by two grant refs or the
> >>>>   same) two or more times means get_user_pages() cannot find the right
> >>>>   page() since m2p override is many-to-one.
> >>>
> >>> Did anybody proposed any ways to fix this issue?
> >>> We have the same problem on ARM in p2m.c and I cannot see any way to
> >>> solve the issue without slowing down the mfn to pfn conversion too much.
> >>
> >> I was planning to add an array of pages to the vma and use this in
> >> get_user_pages() (instead of the page table walk).

FWIW the classic-XenoLinux patches did something similar (if not
identical) to this.
 
> > That is a bit too concise.
> > Does that mean you are not going to fix the mfn to pfn conversion
> > problem and instead change the common code implementation of
> > get_user_pages?
> 
> Yes.  It's impossible to fix mfn_to_pfn() for foreign MFNs.
> 
> David
> 
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