Patch "x86/boot: Fix kdump, cleanup aborted E820_PRAM max_pfn manipulation" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

x86/boot: Fix kdump, cleanup aborted E820_PRAM max_pfn manipulation

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-boot-fix-kdump-cleanup-aborted-e820_pram-max_pfn-manipulation.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dan Williams <[email protected]>
Date: Wed, 21 Sep 2016 12:50:45 -0700
Subject: x86/boot: Fix kdump, cleanup aborted E820_PRAM max_pfn manipulation

From: Dan Williams <[email protected]>

commit 917db484dc6a69969d317b3e57add4208a8d9d42 upstream.

In commit:

ec776ef6bbe1 ("x86/mm: Add support for the non-standard protected e820 type")

Christoph references the original patch I wrote implementing pmem support. The intent of the 'max_pfn' changes in that commit were to enable persistent memory ranges to be covered by the struct page memmap by default.

However, that approach was abandoned when Christoph ported the patches [1], and that functionality has since been replaced by devm_memremap_pages().

In the meantime, this max_pfn manipulation is confusing kdump [2] that assumes that everything covered by the max_pfn is "System RAM". This results in kdump hanging or crashing.

[1]: https://lists.01.org/pipermail/linux-nvdimm/2015-March/000348.html
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1351098

So fix it.

---
 arch/x86/kernel/e820.c |   14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

@@ -348,7 +348,7 @@ int __init sanitize_e820_map(struct e820
 		 * continue building up new bios map based on this
 		 * information
 		 */
-		if (current_type != last_type || current_type == E820_PRAM) {
+		if (current_type != last_type) {
 			if (last_type != 0)	 {
 				new_bios[new_bios_entry].size =
 					change_point[chgidx]->addr - last_addr;

@@ -754,7 +754,7 @@ u64 __init early_reserve_e820(u64 size,
 /*
  * Find the highest page frame number we have available
  */
-static unsigned long __init e820_end_pfn(unsigned long limit_pfn)
+static unsigned long __init e820_end_pfn(unsigned long limit_pfn, unsigned type)
 {
 	int i;
 	unsigned long last_pfn = 0;

@@ -765,11 +765,7 @@ static unsigned long __init e820_end_pfn
 		unsigned long start_pfn;
 		unsigned long end_pfn;
 
-		/*
-		 * Persistent memory is accounted as ram for purposes of
-		 * establishing max_pfn and mem_map.
-		 */
-		if (ei->type != E820_RAM && ei->type != E820_PRAM)
+		if (ei->type != type)
 			continue;
 
 		start_pfn = ei->addr >> PAGE_SHIFT;

@@ -794,12 +790,12 @@ static unsigned long __init e820_end_pfn
 }
 unsigned long __init e820_end_of_ram_pfn(void)
 {
-	return e820_end_pfn(MAX_ARCH_PFN);
+	return e820_end_pfn(MAX_ARCH_PFN, E820_RAM);
 }
 
 unsigned long __init e820_end_of_low_ram_pfn(void)
 {
-	return e820_end_pfn(1UL << (32-PAGE_SHIFT));
+	return e820_end_pfn(1UL << (32 - PAGE_SHIFT), E820_RAM);
 }
 
 static void early_panic(char *msg)

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/x86-boot-fix-kdump-cleanup-aborted-e820_pram-max_pfn-manipulation.patch