[PATCH v2] arm64: mm: Fix memmap to be initialized for the entire section

[Robert Richter]

On ThunderX systems with certain memory configurations we see the
following BUG_ON():

 kernel BUG at mm/page_alloc.c:1848!

This happens for some configs with 64k page size enabled. The BUG_ON()
checks if start and end page of a memmap range belongs to the same
zone.

The BUG_ON() check fails if a memory zone contains NOMAP regions. In
this case the node information of those pages is not initialized. This
causes an inconsistency of the page links with wrong zone and node
information for that pages. NOMAP pages from node 1 still point to the
mem zone from node 0 and have the wrong nid assigned.

The reason for the mis-configuration is a change in pfn_valid() which
reports pages marked NOMAP as invalid:

 68709f45385a arm64: only consider memblocks with NOMAP cleared for linear mapping

This causes pages marked as nomap being no long reassigned to the new
zone in memmap_init_zone() by calling __init_single_pfn().

Fixing this by restoring the old behavior of pfn_valid() to use
memblock_is_memory(). Also changing users of pfn_valid() in arm64 code
to use memblock_is_map_memory() where necessary. This only affects
code in ioremap.c. The code in mmu.c still can use the new version of
pfn_valid().

As a consequence, pfn_valid() can not be used to check if a physical
page is RAM. It just checks if there is an underlying memmap with a
valid struct page. Moreover, for performance reasons the whole memmap
(with pageblock_nr_pages number of pages) has valid pfns (SPARSEMEM
config). The memory range is extended to fit the alignment of the
memmap. Thus, pfn_valid() may return true for pfns that do not map to
physical memory. Those pages are simply not reported to the mm, they
are not marked reserved nor added to the list of free pages. Other
functions such a page_is_ram() or memblock_is_map_ memory() must be
used to check for memory and if the page can be mapped with the linear
mapping.

Since NOMAP mem ranges may need to be mapped with different mem
attributes (e.g. read-only or non-caching) we can not use linear
mapping here. The use of memblock_is_memory() in pfn_valid() may not
break this behaviour. Since commit:

 e7cd190385d1 arm64: mark reserved memblock regions explicitly in iomem

NOMAP mem resources are no longer marked as system RAM (IORESOURCE_
SYSTEM_RAM). Now page_is_ram() and region_intersects() (see
memremap()) do not detect NOMAP mem as system ram and NOMAP mem is not
added to the linear mapping as system RAM is.

v2:

 * Added Ack
 * updated description to reflect the discussion

Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Robert Richter <rrichter@xxxxxxxxxx>
---
 arch/arm64/mm/init.c    | 2 +-
 arch/arm64/mm/ioremap.c | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 212c4d1e2f26..166911f4a2e6 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -147,7 +147,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 #ifdef CONFIG_HAVE_ARCH_PFN_VALID
 int pfn_valid(unsigned long pfn)
 {
-	return memblock_is_map_memory(pfn << PAGE_SHIFT);
+	return memblock_is_memory(pfn << PAGE_SHIFT);
 }
 EXPORT_SYMBOL(pfn_valid);
 #endif
diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
index 01e88c8bcab0..c17c220b0c48 100644
--- a/arch/arm64/mm/ioremap.c
+++ b/arch/arm64/mm/ioremap.c
@@ -21,6 +21,7 @@
  */
 
 #include <linux/export.h>
+#include <linux/memblock.h>
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include <linux/io.h>
@@ -55,7 +56,7 @@ static void __iomem *__ioremap_caller(phys_addr_t phys_addr, size_t size,
 	/*
 	 * Don't allow RAM to be mapped.
 	 */
-	if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
+	if (WARN_ON(memblock_is_map_memory(phys_addr)))
 		return NULL;
 
 	area = get_vm_area_caller(size, VM_IOREMAP, caller);
@@ -96,7 +97,7 @@ EXPORT_SYMBOL(__iounmap);
 void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size)
 {
 	/* For normal memory we already have a cacheable mapping. */
-	if (pfn_valid(__phys_to_pfn(phys_addr)))
+	if (memblock_is_map_memory(phys_addr))
 		return (void __iomem *)__phys_to_virt(phys_addr);
 
 	return __ioremap_caller(phys_addr, size, __pgprot(PROT_NORMAL),
-- 
2.1.4