Re: [Xen-devel] Xen/ARM: Xen queries

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-08-04 at 11:40 +0100, Stefano Stabellini wrote:
> > DOM0 allocates a page for LPI configuration and write start address of
> > this page (IPA)
> > is written to register PROP_BASER. which is trapped.
> > Now DOM0 uses this allocated page to configure LPI's, which is not trapped.
> > 
> > I want to trap on any writes to this page. so that LPI's can be
> > enabled/disabled.
> > Is there any API in Xen to unmap Dom's page so that Xen can get trap
> > on read/writes
> > to this page ?
> 
> Usually these pages are part of an MMIO region that is not mapped in the
> first place.

This specific page is allocated by the guest from it's normal RAM
allocation and then programmed into the GIC durinig initialisation, so
it's not the same as the cases you are thinking of.

I don't think we have a specific function which can be used directly for
this, but something based on apply_p2m_changes ought to do the job.

The biggest question is what p2m_type_t this mapping should have after
the change. p2m_ram_ro is wrong and p2m_mmio_direct doesn't fit either,
the rest are clearly not appropriate.

x86 has "p2m_mmio_dm" which is not dissimilar to this situation, except
it is Xen and not a DM which handles it. Using the same name for
consistency might be good. Otherwise perhaps just p2m_mmio?

CCing Tim for input on what type x86 Xen uses for similar mappings
there.

Ian.


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