Re: [Xen-devel] arm: How DomU access to iomem is implemented

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Sat, 8 Jun 2013, Andrii Anisov wrote:
> Hello,
> Could you please clarify how DomU gets an access to iomem (for ARMv7VE)?
> We traced that iomem configuration of the DomU comes to hypervisor with 
> XEN_DOMCTL_iomem_permissionÂdomctl. Here iomem space is
> added to domain'sÂiomem_caps ranges. But we did not found how these ranges 
> are actually mapped for DomU. Really these
> configuration looks unused, on our board DomU is killed by hypervisor once it 
> tries to access f.e. real UART.
> 
> Actually we did a workaround by mapping regions using map_mmio_regions() 
> right here inÂXEN_DOMCTL_iomem_permission handling. But
> it's a real hack, and it would good to know proper way to get stuff working.

Unfortunately we didn't get around to implementing device assignment
yet, so for the moment you might have to use workarounds to get it to
work.

In any cases XEN_DOMCTL_iomem_permission is used with PV guests that
don't use nested paging (second state translation) in hardware, so it is
not the right hypercall to call for ARM guests.

Like Julien wrote, the right hypercall to call is
xc_domain_memory_mapping/XEN_DOMCTL_memory_mapping, that is missing on
ARM. However you should be able to write it, basing your implementation
on map_mmio_regions.

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