[PATCH v3] arm64: mm: Fix NOMAP page initialization
From: Ard Biesheuvel <hidden>
Date: 2017-01-04 13:57:49
Also in:
linux-mm, lkml
On 16 December 2016 at 16:54, Robert Richter [off-list ref] wrote:
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 longer reassigned to the new zone in memmap_init_zone() by calling __init_single_pfn(). Fixing this by implementing an arm64 specific early_pfn_valid(). This causes all pages of sections with memory including NOMAP ranges to be initialized by __init_single_page() and ensures consistency of page links to zone, node and section.
I like this solution a lot better than the first one, but I am still somewhat uneasy about having the kernel reason about attributes of pages it should not touch in the first place. But the fact that early_pfn_valid() is only used a single time in the whole kernel does give some confidence that we are not simply moving the problem elsewhere. Given that you are touching arch/arm/ as well as arch/arm64, could you explain why only arm64 needs this treatment? Is it simply because we don't have NUMA support there? Considering that Hisilicon D05 suffered from the same issue, I would like to get some coverage there as well. Hanjun, is this something you can arrange? Thanks
quoted hunk ↗ jump to hunk
The HAVE_ARCH_PFN_VALID config option now requires an explicit definiton of early_pfn_valid() in the same way as pfn_valid(). This allows a customized implementation of early_pfn_valid() which redirects to valid_section() for arm64. This is the same as for the generic pfn_valid() implementation. v3: * Use valid_section() which is the same as the default pfn_valid() implementation to initialize * Added Ack for arm/ changes. v2: * Use pfn_present() instead of memblock_is_memory() to support also non-memory NOMAP holes Acked-by: Russell King <redacted> Signed-off-by: Robert Richter <redacted> --- arch/arm/include/asm/page.h | 1 + arch/arm64/include/asm/page.h | 2 ++ arch/arm64/mm/init.c | 15 +++++++++++++++ include/linux/mmzone.h | 5 ++++- 4 files changed, 22 insertions(+), 1 deletion(-)diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h index 4355f0ec44d6..79761bd55f94 100644 --- a/arch/arm/include/asm/page.h +++ b/arch/arm/include/asm/page.h@@ -158,6 +158,7 @@ typedef struct page *pgtable_t; #ifdef CONFIG_HAVE_ARCH_PFN_VALID extern int pfn_valid(unsigned long); +#define early_pfn_valid(pfn) pfn_valid(pfn) #endif #include <asm/memory.h>diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h index 8472c6def5ef..17ceb7435ded 100644 --- a/arch/arm64/include/asm/page.h +++ b/arch/arm64/include/asm/page.h@@ -49,6 +49,8 @@ typedef struct page *pgtable_t; #ifdef CONFIG_HAVE_ARCH_PFN_VALID extern int pfn_valid(unsigned long); +extern int early_pfn_valid(unsigned long); +#define early_pfn_valid early_pfn_valid #endif #include <asm/memory.h>diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 212c4d1e2f26..8ff62a7ff634 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c@@ -145,11 +145,26 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) #endif /* CONFIG_NUMA */ #ifdef CONFIG_HAVE_ARCH_PFN_VALID + int pfn_valid(unsigned long pfn) { return memblock_is_map_memory(pfn << PAGE_SHIFT); } EXPORT_SYMBOL(pfn_valid); + +/* + * This is the same as the generic pfn_valid() implementation. We use + * valid_section() here to make sure all pages of a section including + * NOMAP pages are initialized with __init_single_page(). + */ +int early_pfn_valid(unsigned long pfn) +{ + if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) + return 0; + return valid_section(__nr_to_section(pfn_to_section_nr(pfn))); +} +EXPORT_SYMBOL(early_pfn_valid); + #endif #ifndef CONFIG_SPARSEMEMdiff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 0f088f3a2fed..bedcf8a95881 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h@@ -1170,12 +1170,16 @@ static inline struct mem_section *__pfn_to_section(unsigned long pfn) } #ifndef CONFIG_HAVE_ARCH_PFN_VALID + static inline int pfn_valid(unsigned long pfn) { if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) return 0; return valid_section(__nr_to_section(pfn_to_section_nr(pfn))); } + +#define early_pfn_valid(pfn) pfn_valid(pfn) + #endif static inline int pfn_present(unsigned long pfn)@@ -1200,7 +1204,6 @@ static inline int pfn_present(unsigned long pfn) #define pfn_to_nid(pfn) (0) #endif -#define early_pfn_valid(pfn) pfn_valid(pfn) void sparse_init(void); #else #define sparse_init() do {} while (0) --2.11.0