[Xen-devel] Why does xc_map_foreign_range() refuse to map pfns below 1M from a domU

[Razvan Cojocaru <rzvncj@xxxxxxxxx>]

Hello,

here's the setup: a Windows HVM domU and a Linux PV domU. The Linux
domU wants to map pages from the Windows domU. No XSM involved.

The Linux domU is perfectly able to map (using xc_map_foreign_range())
pages from the Windows domU, except for pages below 1M. For pages
below 1M, it returns "invalid argument". The same code, trying to map
the exact same pages, does succeed, however, if the application trying
to map those pages runs from dom0.

Why is this happening, and can anything be done about it so that the
Linux domU becomes able to map those pages from the HVM Windows domU?


Thanks,
Razvan

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