x86/boot/e820: Print gaps in the E820 table

Gaps in the E820 table are not obvious at a glance and can
easily be overlooked.

Print out gaps in the E820 table:

Before:

	BIOS-provided physical RAM map:
	BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
	BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
	BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff] usable
	BIOS-e820: [mem 0x000000007ffdc000-0x000000007fffffff] reserved
	BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved
	BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
	BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
	BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
	BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff] reserved
After:

	BIOS-provided physical RAM map:
	BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
	BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
	BIOS-e820: [gap 0x00000000000a0000-0x00000000000effff]
	BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
	BIOS-e820: [mem 0x0000000000100000-0x000000007ffdbfff] usable
	BIOS-e820: [mem 0x000000007ffdc000-0x000000007fffffff] reserved
	BIOS-e820: [gap 0x0000000080000000-0x00000000afffffff]
	BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved
	BIOS-e820: [gap 0x00000000c0000000-0x00000000fed1bfff]
	BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
	BIOS-e820: [gap 0x00000000fed20000-0x00000000feffbfff]
	BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
	BIOS-e820: [gap 0x00000000ff000000-0x00000000fffbffff]
	BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
	BIOS-e820: [gap 0x0000000100000000-0x000000fcffffffff]
	BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff] reserved

Also warn about badly ordered E820 table entries:

	BUG: out of order E820 entry!

( this is printed before the entry is printed, so there's no need to
  print any additional data with the warning. )

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20250515120549.2820541-6-mingo@kernel.org

Author: ingomolnar

arch/x86/kernel/e820.c

@@ -202,18 +202,32 @@ static void __init e820_print_type(enum e820_type type)
 
 static void __init e820__print_table(const char *who)
 {
+	u64 range_end_prev = 0;
 	int i;
 
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		struct e820_entry *entry = e820_table->entries + i;
+		u64 range_start, range_end;
 
-		pr_info("%s: [mem %#018Lx-%#018Lx] ",
-			who,
-			entry->addr,
-			entry->addr + entry->size-1);
+		range_start = entry->addr;
+		range_end   = entry->addr + entry->size;
 
+		/* Out of order E820 maps should not happen: */
+		if (range_start < range_end_prev)
+			pr_info(FW_BUG "out of order E820 entry!\n");
+
+		if (range_start > range_end_prev) {
+			pr_info("%s: [gap %#018Lx-%#018Lx]\n",
+				who,
+				range_end_prev,
+				range_start-1);
+		}
+
+		pr_info("%s: [mem %#018Lx-%#018Lx] ", who, range_start, range_end-1);
 		e820_print_type(entry->type);
 		pr_cont("\n");
+
+		range_end_prev = range_end;
 	}
 }