Commit f2f29da9 authored by Myrrh Periwinkle's avatar Myrrh Periwinkle Committed by Ingo Molnar
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x86/e820: Fix handling of subpage regions when calculating nosave ranges in... 


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

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: e8eff5ac ("[PATCH] Make swsusp avoid memory holes and reserved memory regions on x86_64")
Reported-by: default avatarRoberto Ricci <io@r-ricci.it>
Tested-by: default avatarRoberto Ricci <io@r-ricci.it>
Signed-off-by: default avatarMyrrh Periwinkle <myrrhperiwinkle@qtmlabs.xyz>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Len Brown <len.brown@intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250406-fix-e820-nosave-v3-1-f3787bc1ee1d@qtmlabs.xyz
Closes: https://lore.kernel.org/all/Z4WFjBVHpndct7br@desktop0a/
parent 8b37357a

arch/x86/kernel/e820.c

+8 −9
Original line number Diff line number Diff line
@@ -753,22 +753,21 @@ 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)

			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