[Patch] min_low_pfn and max_low_pfn calcultion fix

From: Zou Nan hai <nanhai.zou_at_intel.com>
Date: 2007-02-28 10:38:55
Hi,
  We have seen bad_pte_print when testing crashdump on an SN machine in
recent 2.6.20 kernel. 
  There are tons of bad pte print (pfn < max_low_pfn) reports when the
crash kernel boots up, all those reported bad pages are inside initmem
range;
  That is because if the crash kernel code and data happens to be at the
beginning of the 1st node. build_node_maps in discontig.c will bypass
reserved regions with filter_rsvd_memory. Since min_low_pfn is
calculated in build_node_map, so in this case, min_low_pfn will be
greater than kernel code and data.

  Because pages inside initmem are freed and reused later, we saw
pfn_valid check fail on those pages.

  I think this theoretically happen on a normal kernel. When I check
min_low_pfn and max_low_pfn calculation in contig.c and discontig.c. 
I found more issues than this.
  
  1. min_low_pfn and max_low_pfn calculation is inconsistent between
contig.c and discontig.c, 
  min_low_pfn is calculated as the first page number of boot memmap in
contig.c (Why? Though this may work at the most of the time, I don't
think it is the right logic). It is calculated as the lowest physical
memory page number bypass reserved regions in discontig.c.
  max_low_pfn is calculated include reserved regions in contig.c. It is
calculated exclude reserved regions in discontig.c.
  
  2. If kernel code and data region is happen to be at the begin or the
end of physical memory, when min_low_pfn and max_low_pfn calculation is
bypassed kernel code and data, pages in initmem will report bad.

  3. initrd is also in reserved regions, if it is at the begin or at the
end of physical memory, kernel will refuse to reuse the memory. Because
the virt_addr_valid check in free_initrd_mem.

  So it is better to fix and clean up those issues. 
Calculate min_low_pfn and max_low_pfn in a consistent way.

Below is the patch, please review and comments

Signed-off-by:	Zou Nan hai <nanhai.zou@intel.com>

diff -Nraup a/arch/ia64/mm/contig.c b/arch/ia64/mm/contig.c
--- a/arch/ia64/mm/contig.c	2007-02-27 00:42:06.000000000 -0500
+++ b/arch/ia64/mm/contig.c	2007-02-27 03:03:00.000000000 -0500
@@ -75,26 +75,6 @@ show_mem (void)
 unsigned long bootmap_start;
 
 /**
- * find_max_pfn - adjust the maximum page number callback
- * @start: start of range
- * @end: end of range
- * @arg: address of pointer to global max_pfn variable
- *
- * Passed as a callback function to efi_memmap_walk() to determine the highest
- * available page frame number in the system.
- */
-int
-find_max_pfn (unsigned long start, unsigned long end, void *arg)
-{
-	unsigned long *max_pfnp = arg, pfn;
-
-	pfn = (PAGE_ALIGN(end - 1) - PAGE_OFFSET) >> PAGE_SHIFT;
-	if (pfn > *max_pfnp)
-		*max_pfnp = pfn;
-	return 0;
-}
-
-/**
  * find_bootmap_location - callback to find a memory area for the bootmap
  * @start: start of region
  * @end: end of region
@@ -155,9 +135,10 @@ find_memory (void)
 	reserve_memory();
 
 	/* first find highest page frame number */
-	max_pfn = 0;
-	efi_memmap_walk(find_max_pfn, &max_pfn);
-
+	min_low_pfn = -1;
+	max_low_pfn = 0;
+	efi_memmap_walk(find_max_min_low_pfn, NULL);
+	max_pfn = max_low_pfn;
 	/* how many bytes to cover all the pages */
 	bootmap_size = bootmem_bootmap_pages(max_pfn) << PAGE_SHIFT;
 
@@ -167,7 +148,8 @@ find_memory (void)
 	if (bootmap_start == ~0UL)
 		panic("Cannot find %ld bytes for bootmap\n", bootmap_size);
 
-	bootmap_size = init_bootmem(bootmap_start >> PAGE_SHIFT, max_pfn);
+	bootmap_size = init_bootmem_node(NODE_DATA(0), 
+			(bootmap_start >> PAGE_SHIFT), 0, max_pfn);
 
 	/* Free all available memory, then mark bootmem-map as being in use. */
 	efi_memmap_walk(filter_rsvd_memory, free_bootmem);
diff -Nraup a/arch/ia64/mm/discontig.c b/arch/ia64/mm/discontig.c
--- a/arch/ia64/mm/discontig.c	2007-02-27 00:42:06.000000000 -0500
+++ b/arch/ia64/mm/discontig.c	2007-02-27 03:00:30.000000000 -0500
@@ -86,9 +86,6 @@ static int __init build_node_maps(unsign
 		bdp->node_low_pfn = max(epfn, bdp->node_low_pfn);
 	}
 
-	min_low_pfn = min(min_low_pfn, bdp->node_boot_start>>PAGE_SHIFT);
-	max_low_pfn = max(max_low_pfn, bdp->node_low_pfn);
-
 	return 0;
 }
 
@@ -467,6 +464,7 @@ void __init find_memory(void)
 	/* These actually end up getting called by call_pernode_memory() */
 	efi_memmap_walk(filter_rsvd_memory, build_node_maps);
 	efi_memmap_walk(filter_rsvd_memory, find_pernode_space);
+	efi_memmap_walk(find_max_min_low_pfn, NULL);
 
 	for_each_online_node(node)
 		if (mem_data[node].bootmem_data.node_low_pfn) {
diff -Nraup a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
--- a/arch/ia64/mm/init.c	2007-02-27 00:42:06.000000000 -0500
+++ b/arch/ia64/mm/init.c	2007-02-27 03:08:10.000000000 -0500
@@ -616,6 +616,22 @@ count_reserved_pages (u64 start, u64 end
 	return 0;
 }
 
+int
+find_max_min_low_pfn (unsigned long start, unsigned long end, void *arg)
+{
+	unsigned long pfn_start, pfn_end;
+#if CONFIG_FLATMEM
+	pfn_start = (PAGE_ALIGN(__pa(start))) >> PAGE_SHIFT;
+	pfn_end = (PAGE_ALIGN(__pa(end - 1))) >> PAGE_SHIFT;
+#else
+	pfn_start = GRANULEROUNDDOWN(__pa(start)) >> PAGE_SHIFT;
+	pfn_end = GRANULEROUNDUP(__pa(end - 1)) >> PAGE_SHIFT;
+#endif
+	min_low_pfn = min(min_low_pfn, pfn_start);
+	max_low_pfn = max(max_low_pfn, pfn_end);
+	return 0;
+}
+
 /*
  * Boot command-line option "nolwsys" can be used to disable the use of any light-weight
  * system call handler.  When this option is in effect, all fsyscalls will end up bubbling
diff -Nraup a/include/asm-ia64/meminit.h b/include/asm-ia64/meminit.h
--- a/include/asm-ia64/meminit.h	2007-02-27 00:42:07.000000000 -0500
+++ b/include/asm-ia64/meminit.h	2007-02-27 03:01:15.000000000 -0500
@@ -35,6 +35,7 @@ extern void reserve_memory (void);
 extern void find_initrd (void);
 extern int filter_rsvd_memory (unsigned long start, unsigned long end, void *arg);
 extern void efi_memmap_init(unsigned long *, unsigned long *);
+extern int find_max_min_low_pfn (unsigned long , unsigned long, void *);
 
 /*
  * For rounding an address to the next IA64_GRANULE_SIZE or order





  
	
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Received on Wed Feb 28 12:34:34 2007

This archive was generated by hypermail 2.1.8 : 2007-02-28 12:34:49 EST