Merge tag 'x86-urgent-2026-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Ingo Molnar:

 - Fix memory map enumeration bug in the Xen e820 parsing code (Juergen
   Gross)

 - Re-enable e820 BIOS fallback if e820 table is empty (David Gow)

* tag 'x86-urgent-2026-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/boot/e820: Re-enable BIOS fallback if e820 table is empty
  x86/xen: Fix a potential problem in xen_e820_resolve_conflicts()

Author: torvalds

arch/x86/kernel/e820.c

@@ -450,6 +450,10 @@ __init static int append_e820_table(struct boot_e820_entry *entries, u32 nr_entr
 {
 	struct boot_e820_entry *entry = entries;
 
+	/* If there aren't any entries, we'll want to fall back to another source: */
+	if (!nr_entries)
+		return -ENOENT;
+
 	while (nr_entries) {
 		u64 start = entry->addr;
 		u64 size  = entry->size;
@@ -458,7 +462,7 @@ __init static int append_e820_table(struct boot_e820_entry *entries, u32 nr_entr
 
 		/* Ignore the remaining entries on 64-bit overflow: */
 		if (start > end && likely(size))
-			return -1;
+			return -EINVAL;
 
 		e820__range_add(start, size, type);
 

arch/x86/xen/setup.c

@@ -695,17 +695,22 @@ static void __init xen_e820_resolve_conflicts(phys_addr_t start,
 		return;
 
 	end = start + size;
-	entry = xen_e820_table.entries;
+	mapcnt = 0;
 
-	for (mapcnt = 0; mapcnt < xen_e820_table.nr_entries; mapcnt++) {
+	while (mapcnt < xen_e820_table.nr_entries) {
+		entry = xen_e820_table.entries + mapcnt;
 		if (entry->addr >= end)
 			return;
 
 		if (entry->addr + entry->size > start &&
-		    entry->type == E820_TYPE_NVS)
+		    entry->type == E820_TYPE_NVS) {
 			xen_e820_swap_entry_with_ram(entry);
+			/* E820 map has been changed, restart loop! */
+			mapcnt = 0;
+			continue;
+		}
 
-		entry++;
+		mapcnt++;
 	}
 }