x86/xen: fix set_phys_range_identity() if pfn_e > MAX_P2M_PFN

Allow set_phys_range_identity() to work with a range that overlaps
MAX_P2M_PFN by clamping pfn_e to MAX_P2M_PFN.
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

@@ -774,7 +774,7 @@ unsigned long __init set_phys_range_identity(unsigned long pfn_s,
 {
 	unsigned long pfn;
 
-	if (unlikely(pfn_s >= MAX_P2M_PFN || pfn_e >= MAX_P2M_PFN))
+	if (unlikely(pfn_s >= MAX_P2M_PFN))
 		return 0;
 
 	if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
@@ -783,6 +783,9 @@ unsigned long __init set_phys_range_identity(unsigned long pfn_s,
 	if (pfn_s > pfn_e)
 		return 0;
 
+	if (pfn_e > MAX_P2M_PFN)
+		pfn_e = MAX_P2M_PFN;
+
 	for (pfn = (pfn_s & ~(P2M_MID_PER_PAGE * P2M_PER_PAGE - 1));
 		pfn < ALIGN(pfn_e, (P2M_MID_PER_PAGE * P2M_PER_PAGE));
 		pfn += P2M_MID_PER_PAGE * P2M_PER_PAGE)