[Xen-devel] get_page_from_gfn() for foreign pages

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

Whilst debugging my PV-IOMMU code I ran into an issue with get_page_from_gfn(): 
It is failing when the gfn in question is actually a grant map from another 
domain, and the reason for this is that get_page(page, domain) explicitly fails 
if the page owner is not the domain specified to the call. However, I find that 
ARM implementation of get_page_from_gfn() has a test for foreign p2m entries 
and completes successfully (by avoiding a call to get_page() and instead 
calling page_get_owner_and_reference() directly).

I can't think of any particular reason why, on x86, get_page_from_gfn() should 
not work for foreign mapped or grant mapped pages. Does anyone know why the 
restriction is there?

  Cheers,

    Paul

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