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... Closes: https://lore.kernel.org/all/Z4WFjBVHpndct7br@desktop0a/ (cherry picked from commit f2f29da9f0d4367f6ff35e0d9d021257bb53e273) Signed-off-by: Myrrh Periwinkle myrrhperiwinkle@qtmlabs.xyz --- 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 7da2bcd2b8eb..f826c0a60a29 100644 --- a/arch/x86/kernel/e820.c +++ b/arch/x86/kernel/e820.c @@ -738,22 +738,21 @@ 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