[Xen-devel] Re: HYBRID: gnttab_map() to map shared frames..

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-10-18 at 03:18 +0100, Mukesh Rathor wrote:
> Hi Jeremy,
> 
> You have any thoughts on this? This is basically for hybrid running 
> autotranslate paging mode.  I am trying to figure how to get unmapped
> pfns to map shared grant table page/s from xen. HVM does this via
> pci_resource_start() and gets io remapped address. However, in case of
> pure PV, I am not sure how feasible this approach would be.
> 
> Is there way I can reserve few pfn's above max_pfn and use those
> for my XENMAPSPACE_grant_table call?

I think we should avoid exposing any sort of magic PCI bus to PV/hybrid
guests.

Could GNTTABOP_setup_table return GFNs from the very top of the GFN
space? Perhaps even above what would be architecturally valid, although
perhaps that is incompatible with HAP. Anything above max_pfn would seem
to be valid for the hypervisor to place "magic" mappings in?

Another approach might be to take advantage of the fact that a modern PV
kernel will call XENMEM_memory_map to obtain an e820 describing its
pseudo-physical address space. You could arrange for there to be some
reserved space returned in that.

Ian.



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