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Re: X server in dom0: Bad VBT signature

On Tue, Sep 04, 2012 at 03:32:23PM +0200, Gianluca Guida wrote:
> On Tue, Sep 04, 2012 at 02:29:10PM +0200, Manuel Bouyer wrote:
> > On Tue, Sep 04, 2012 at 02:12:39PM +0200, Gianluca Guida wrote:
> > > 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 ?
> My memory isn't helping me here, as the last time I looked at this code
> in the Linux kernel was in 2009, and then I've stopped working on Xen
> for almost two years, but:
> IIRC Linux's dom0 kernel gives back the memory to Xen. I will look at

Right. It also then calls populate_physmap back on the amount of memory
it returned - and sticks those in the E820_RAM sections.

The end result is that the the P2M tree mirrors the E820 and we the
'ram' pages are only in the E820_RAM regions.

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