From bd6eae1f30bfe5093a85d8a9ad8efb92fde92a21 Mon Sep 17 00:00:00 2001
From: Myrrh Periwinkle <myrrhperiwinkle@qtmlabs.xyz>
Date: Sun, 6 Apr 2025 11:45:22 +0700
Subject: [PATCH] x86/e820: Fix handling of subpage regions when calculating
nosave ranges in e820__register_nosave_regions()
commit f2f29da9f0d4367f6ff35e0d9d021257bb53e273 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: e8eff5ac294e ("[PATCH] Make swsusp avoid memory holes and reserved memory regions on x86_64")
Reported-by: Roberto Ricci <io@r-ricci.it>
Tested-by: Roberto Ricci <io@r-ricci.it>
Signed-off-by: Myrrh Periwinkle <myrrhperiwinkle@qtmlabs.xyz>
Signed-off-by: Ingo 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/
Signed-off-by: Myrrh Periwinkle <myrrhperiwinkle@qtmlabs.xyz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/e820.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 4893d30ce4384..b4746eb8b1152 100644
--- a/arch/x86/kernel/e820.c
+++ b/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