[PATCH] x86/e820: Fix handling of subpage regions when calculating nosave ranges

[PATCH] x86/e820: Fix handling of subpage regions when calculating nosave ranges

[msizanoen]

Handle better cases where there might be non-page-aligned RAM e820
regions so we don't end up marking kernel memory as nosave.

This also simplifies the calculation of nosave ranges by treating
non-RAM regions as holes.

Fixes: e5540f875404 ("x86/boot/e820: Consolidate 'struct e820_entry *entry' local variable names")
Tested-by: Roberto Ricci <io@r-ricci.it>
Reported-by: Roberto Ricci <io@r-ricci.it>
Closes: https://lore.kernel.org/all/Z4WFjBVHpndct7br@desktop0a/
Signed-off-by: msizanoen <msizanoen@qtmlabs.xyz>
Cc: stable@vger.kernel.org
---
The issue of the kernel failing to resume from hibernation after
kexec_load() is used is likely due to kexec-tools passing in a different
e820 memory map from the one provided by system firmware, causing the
e820 consistency check to fail. That issue is not addressed in this
patch and will need to be fixed in kexec-tools instead.
---
 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 57120f0749cc3c23844eeb36820705687e08bbf7..656ed7abd28de180b842a8d7993e9708f9f17026 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -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_UP(last_addr), PFN_DOWN(entry->addr));
+
+		last_addr = entry->addr + entry->size;
 	}
+
+	register_nosave_region(PFN_UP(last_addr), limit_pfn);
 }
 
 #ifdef CONFIG_ACPI

---
base-commit: e48e99b6edf41c69c5528aa7ffb2daf3c59ee105
change-id: 20250405-fix-e820-nosave-c43779583abe

Best regards,
-- 
msizanoen <msizanoen@qtmlabs.xyz>

Re: [PATCH] x86/e820: Fix handling of subpage regions when calculating nosave ranges

[Greg KH]

On Sat, Apr 05, 2025 at 10:09:24AM +0700, msizanoen wrote:
> Handle better cases where there might be non-page-aligned RAM e820
> regions so we don't end up marking kernel memory as nosave.
> 
> This also simplifies the calculation of nosave ranges by treating
> non-RAM regions as holes.
> 
> Fixes: e5540f875404 ("x86/boot/e820: Consolidate 'struct e820_entry *entry' local variable names")
> Tested-by: Roberto Ricci <io@r-ricci.it>
> Reported-by: Roberto Ricci <io@r-ricci.it>
> Closes: https://lore.kernel.org/all/Z4WFjBVHpndct7br@desktop0a/
> Signed-off-by: msizanoen <msizanoen@qtmlabs.xyz>

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