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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-12-03 at 17:06 +0200, Razvan Cojocaru wrote:
> 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.

With no XSM how does it have the privilege to do this?

>  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.

For dom0 it works because by default dom0 has the foreign mapping
privilege.

> 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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