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Re: X server in dom0: Bad VBT signature

On Tue, Sep 04, 2012 at 02:12:39PM +0200, Gianluca Guida wrote:
> Nope.
> This is only partially true. Xen also gives us a memory map through
> memory_op hypercall (for dom0, it actually gives us something pretty
> similar to the host e820).
> With this information, we can map the I/O space and other non-RAM pieces
> of memory to identity mapping that access the actual physical memory of
> the host (I am talking about dom0 case here, clearly).

And what do you do with ram that Xen did give us at these addresses ?
remap it somewhere else ?

The identity mapping isn't even needed, if the address is not in a
ram segment it's a machine address.

But such a hack doesn't solve the underlying problem which is,
basically, that under Xen, physical and machine addresses are
different address spaces.

> This requires of course handling our own p2m table, not sure if NetBSD
> does this currently.

I'm not sure what you mean here. When we get some external page
(e.g. from a domU) m2p/p2m is updated accordingly.
If you mean rebuilding a m2p/p2m from scratch, we don't do that.

Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference

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