x86/e820: Fix handling of subpage regions when calculating nosave ranges in e820__register_nosave_regions()

commit f2f29da upstream.

While debugging kexec/hibernation hangs and crashes, it turned out that
the current implementation of e820__register_nosave_regions() suffers from
multiple serious issues:

 - The end of last region is tracked by PFN, causing it to find holes
   that aren't there if two consecutive subpage regions are present

 - The nosave PFN ranges derived from holes are rounded out (instead of
   rounded in) which makes it inconsistent with how explicitly reserved
   regions are handled

Fix this by:

 - Treating reserved regions as if they were holes, to ensure consistent
   handling (rounding out nosave PFN ranges is more correct as the
   kernel does not use partial pages)

 - Tracking the end of the last RAM region by address instead of pages
   to detect holes more precisely

These bugs appear to have been introduced about ~18 years ago with the very
first version of e820_mark_nosave_regions(), and its flawed assumptions were
carried forward uninterrupted through various waves of rewrites and renames.

[ mingo: Added Git archeology details, for kicks and giggles. ]

Fixes: e8eff5a ("[PATCH] Make swsusp avoid memory holes and reserved memory regions on x86_64")
Reported-by: Roberto Ricci <[email protected]>
Tested-by: Roberto Ricci <[email protected]>
Signed-off-by: Myrrh Periwinkle <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Len Brown <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Closes: https://lore.kernel.org/all/Z4WFjBVHpndct7br@desktop0a/
Signed-off-by: Myrrh Periwinkle <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: msizanoen1

arch/x86/kernel/e820.c

@@ -754,22 +754,21 @@ void __init e820__memory_setup_extended(u64 phys_addr, u32 data_len)
 void __init e820__register_nosave_regions(unsigned long limit_pfn)
 {
 	int i;
-	unsigned long pfn = 0;
+	u64 last_addr = 0;
 
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		struct e820_entry *entry = &e820_table->entries[i];
 
-		if (pfn < PFN_UP(entry->addr))
-			register_nosave_region(pfn, PFN_UP(entry->addr));
-
-		pfn = PFN_DOWN(entry->addr + entry->size);
-
 		if (entry->type != E820_TYPE_RAM && entry->type != E820_TYPE_RESERVED_KERN)
-			register_nosave_region(PFN_UP(entry->addr), pfn);
+			continue;
 
-		if (pfn >= limit_pfn)
-			break;
+		if (last_addr < entry->addr)
+			register_nosave_region(PFN_DOWN(last_addr), PFN_UP(entry->addr));
+
+		last_addr = entry->addr + entry->size;
 	}
+
+	register_nosave_region(PFN_DOWN(last_addr), limit_pfn);
 }
 
 #ifdef CONFIG_ACPI