x86/xen: set regions above the end of RAM as 1:1

PCI devices may have BARs located above the end of RAM so mark such
frames as identity frames in the p2m (instead of the default of
missing).

PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
identity frames for the same reason.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/p2m.c

@@ -507,7 +507,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
 	unsigned topidx, mididx, idx;
 
 	if (unlikely(pfn >= MAX_P2M_PFN))
-		return INVALID_P2M_ENTRY;
+		return IDENTITY_FRAME(pfn);
 
 	topidx = p2m_top_index(pfn);
 	mididx = p2m_mid_index(pfn);

arch/x86/xen/setup.c

@@ -468,6 +468,15 @@ char * __init xen_memory_setup(void)
 			i++;
 	}
 
+	/*
+	 * Set the rest as identity mapped, in case PCI BARs are
+	 * located here.
+	 *
+	 * PFNs above MAX_P2M_PFN are considered identity mapped as
+	 * well.
+	 */
+	set_phys_range_identity(map[i-1].addr / PAGE_SIZE, ~0ul);
+
 	/*
 	 * In domU, the ISA region is normal, usable memory, but we
 	 * reserve ISA memory anyway because too many things poke