[PATCH V5 0/2] mm/debug: Add tests validating architecture page table helpers

[PATCH V5 0/2] mm/debug: Add tests validating architecture page table helpers

[Anshuman Khandual]

This series adds a test validation for architecture exported page table
helpers. Patch in the series adds basic transformation tests at various
levels of the page table. Before that it exports gigantic page allocation
function from HugeTLB.

This test was originally suggested by Catalin during arm64 THP migration
RFC discussion earlier. Going forward it can include more specific tests
with respect to various generic MM functions like THP, HugeTLB etc and
platform specific tests.

https://lore.kernel.org/linux-mm/20190628102003.GA56463 at arrakis.emea.arm.com/

Changes in V5:

- Redefined and moved X86 mm_p4d_folded() into a different header per Kirill/Ingo
- Updated the config option comment per Ingo and dropped 'kernel module' reference
- Updated the commit message and dropped 'kernel module' reference
- Changed DEBUG_ARCH_PGTABLE_TEST into DEBUG_VM_PGTABLE per Ingo
- Moved config option from mm/Kconfig.debug into lib/Kconfig.debug
- Renamed core test function arch_pgtable_tests() as debug_vm_pgtable()
- Renamed mm/arch_pgtable_test.c as mm/debug_vm_pgtable.c
- debug_vm_pgtable() gets called from kernel_init_freeable() after init_mm_internals()
- Added an entry in Documentation/features/debug/ per Ingo
- Enabled the test on arm64 and x86 platforms for now

Changes in V4: (https://patchwork.kernel.org/project/linux-mm/list/?series=183465)

- Disable DEBUG_ARCH_PGTABLE_TEST for ARM and IA64 platforms

Changes in V3: (https://lore.kernel.org/patchwork/project/lkml/list/?series=411216)

- Changed test trigger from module format into late_initcall()
- Marked all functions with __init to be freed after completion
- Changed all __PGTABLE_PXX_FOLDED checks as mm_pxx_folded()
- Folded in PPC32 fixes from Christophe

Changes in V2:

https://lore.kernel.org/linux-mm/1568268173-31302-1-git-send-email-anshuman.khandual at arm.com/T/#t

- Fixed small typo error in MODULE_DESCRIPTION()
- Fixed m64k build problems for lvalue concerns in pmd_xxx_tests()
- Fixed dynamic page table level folding problems on x86 as per Kirril
- Fixed second pointers during pxx_populate_tests() per Kirill and Gerald
- Allocate and free pte table with pte_alloc_one/pte_free per Kirill
- Modified pxx_clear_tests() to accommodate s390 lower 12 bits situation
- Changed RANDOM_NZVALUE value from 0xbe to 0xff
- Changed allocation, usage, free sequence for saved_ptep
- Renamed VMA_FLAGS as VMFLAGS
- Implemented a new method for random vaddr generation
- Implemented some other cleanups
- Dropped extern reference to mm_alloc()
- Created and exported new alloc_gigantic_page_order()
- Dropped the custom allocator and used new alloc_gigantic_page_order()

Changes in V1:

https://lore.kernel.org/linux-mm/1567497706-8649-1-git-send-email-anshuman.khandual at arm.com/

- Added fallback mechanism for PMD aligned memory allocation failure

Changes in RFC V2:

https://lore.kernel.org/linux-mm/1565335998-22553-1-git-send-email-anshuman.khandual at arm.com/T/#u

- Moved test module and it's config from lib/ to mm/
- Renamed config TEST_ARCH_PGTABLE as DEBUG_ARCH_PGTABLE_TEST
- Renamed file from test_arch_pgtable.c to arch_pgtable_test.c
- Added relevant MODULE_DESCRIPTION() and MODULE_AUTHOR() details
- Dropped loadable module config option
- Basic tests now use memory blocks with required size and alignment
- PUD aligned memory block gets allocated with alloc_contig_range()
- If PUD aligned memory could not be allocated it falls back on PMD aligned
  memory block from page allocator and pud_* tests are skipped
- Clear and populate tests now operate on real in memory page table entries
- Dummy mm_struct gets allocated with mm_alloc()
- Dummy page table entries get allocated with [pud|pmd|pte]_alloc_[map]()
- Simplified [p4d|pgd]_basic_tests(), now has random values in the entries

Original RFC V1:

https://lore.kernel.org/linux-mm/1564037723-26676-1-git-send-email-anshuman.khandual at arm.com/

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Steven Price <Steven.Price at arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Sri Krishna chowdary <schowdary at nvidia.com>
Cc: Dave Hansen <dave.hansen at intel.com>
Cc: Russell King - ARM Linux <linux at armlinux.org.uk>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Vineet Gupta <vgupta at synopsys.com>
Cc: James Hogan <jhogan at kernel.org>
Cc: Paul Burton <paul.burton at mips.com>
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: Kirill A. Shutemov <kirill at shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer at de.ibm.com>
Cc: Christophe Leroy <christophe.leroy at c-s.fr>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: linux-snps-arc at lists.infradead.org
Cc: linux-mips at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-ia64 at vger.kernel.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: linux-s390 at vger.kernel.org
Cc: linux-sh at vger.kernel.org
Cc: sparclinux at vger.kernel.org
Cc: x86 at kernel.org
Cc: linux-kernel at vger.kernel.org

Anshuman Khandual (2):
  mm/hugetlb: Make alloc_gigantic_page() available for general use
  mm/debug: Add tests validating architecture page table helpers

 .../debug/debug-vm-pgtable/arch-support.txt        |  34 ++
 arch/arm64/Kconfig                                 |   1 +
 arch/x86/Kconfig                                   |   1 +
 arch/x86/include/asm/pgtable_64.h                  |   6 +
 include/asm-generic/pgtable.h                      |   6 +
 include/linux/hugetlb.h                            |   9 +
 init/main.c                                        |   1 +
 lib/Kconfig.debug                                  |  21 +
 mm/Makefile                                        |   1 +
 mm/debug_vm_pgtable.c                              | 438 +++++++++++++++++++++
 mm/hugetlb.c                                       |  24 +-
 11 files changed, 540 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/features/debug/debug-vm-pgtable/arch-support.txt
 create mode 100644 mm/debug_vm_pgtable.c

-- 
2.7.4

[PATCH V5 1/2] mm/hugetlb: Make alloc_gigantic_page() available for general use

[Anshuman Khandual]

alloc_gigantic_page() implements an allocation method where it scans over
various zones looking for a large contiguous memory block which could not
have been allocated through the buddy allocator. A subsequent patch which
tests arch page table helpers needs such a method to allocate PUD_SIZE
sized memory block. In the future such methods might have other use cases
as well. So alloc_gigantic_page() has been split carving out actual memory
allocation method and made available via new alloc_gigantic_page_order().

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Steven Price <Steven.Price at arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Sri Krishna chowdary <schowdary at nvidia.com>
Cc: Dave Hansen <dave.hansen at intel.com>
Cc: Russell King - ARM Linux <linux at armlinux.org.uk>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Vineet Gupta <vgupta at synopsys.com>
Cc: James Hogan <jhogan at kernel.org>
Cc: Paul Burton <paul.burton at mips.com>
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: Kirill A. Shutemov <kirill at shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer at de.ibm.com>
Cc: Christophe Leroy <christophe.leroy at c-s.fr>
Cc: linux-snps-arc at lists.infradead.org
Cc: linux-mips at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-ia64 at vger.kernel.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: linux-s390 at vger.kernel.org
Cc: linux-sh at vger.kernel.org
Cc: sparclinux at vger.kernel.org
Cc: x86 at kernel.org
Cc: linux-kernel at vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 include/linux/hugetlb.h |  9 +++++++++
 mm/hugetlb.c            | 24 ++++++++++++++++++++++--
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 4c5a16b..7ff1e36 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -298,6 +298,9 @@ static inline bool is_file_hugepages(struct file *file)
 }
 
 
+struct page *
+alloc_gigantic_page_order(unsigned int order, gfp_t gfp_mask,
+			  int nid, nodemask_t *nodemask);
 #else /* !CONFIG_HUGETLBFS */
 
 #define is_file_hugepages(file)			false
@@ -309,6 +312,12 @@ hugetlb_file_setup(const char *name, size_t size, vm_flags_t acctflag,
 	return ERR_PTR(-ENOSYS);
 }
 
+static inline struct page *
+alloc_gigantic_page_order(unsigned int order, gfp_t gfp_mask,
+			  int nid, nodemask_t *nodemask)
+{
+	return NULL;
+}
 #endif /* !CONFIG_HUGETLBFS */
 
 #ifdef HAVE_ARCH_HUGETLB_UNMAPPED_AREA
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 977f9a3..2996e44 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1066,10 +1066,9 @@ static bool zone_spans_last_pfn(const struct zone *zone,
 	return zone_spans_pfn(zone, last_pfn);
 }
 
-static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
+struct page *alloc_gigantic_page_order(unsigned int order, gfp_t gfp_mask,
 		int nid, nodemask_t *nodemask)
 {
-	unsigned int order = huge_page_order(h);
 	unsigned long nr_pages = 1 << order;
 	unsigned long ret, pfn, flags;
 	struct zonelist *zonelist;
@@ -1105,6 +1104,14 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 	return NULL;
 }
 
+static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
+					int nid, nodemask_t *nodemask)
+{
+	unsigned int order = huge_page_order(h);
+
+	return alloc_gigantic_page_order(order, gfp_mask, nid, nodemask);
+}
+
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
 static void prep_compound_gigantic_page(struct page *page, unsigned int order);
 #else /* !CONFIG_CONTIG_ALLOC */
@@ -1113,6 +1120,12 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 {
 	return NULL;
 }
+
+struct page *alloc_gigantic_page_order(unsigned int order, gfp_t gfp_mask,
+				       int nid, nodemask_t *nodemask)
+{
+	return NULL;
+}
 #endif /* CONFIG_CONTIG_ALLOC */
 
 #else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE */
@@ -1121,6 +1134,13 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 {
 	return NULL;
 }
+
+struct page *alloc_gigantic_page_order(unsigned int order, gfp_t gfp_mask,
+				       int nid, nodemask_t *nodemask)
+{
+	return NULL;
+}
+
 static inline void free_gigantic_page(struct page *page, unsigned int order) { }
 static inline void destroy_compound_gigantic_page(struct page *page,
 						unsigned int order) { }
-- 
2.7.4

[PATCH V5 2/2] mm/debug: Add tests validating architecture page table helpers

[Anshuman Khandual]

This adds tests which will validate architecture page table helpers and
other accessors in their compliance with expected generic MM semantics.
This will help various architectures in validating changes to existing
page table helpers or addition of new ones.

Test page table and memory pages creating it's entries at various level are
all allocated from system memory with required size and alignments. But if
memory pages with required size and alignment could not be allocated, then
all depending individual tests are just skipped afterwards. This test gets
called right after init_mm_internals() required for alloc_contig_range() to
work correctly.

This gets build and run when CONFIG_DEBUG_VM_PGTABLE is selected along with
CONFIG_VM_DEBUG. Architectures willing to subscribe this test also need to
select CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE which for now is limited to x86 and
arm64. Going forward, other architectures too can enable this after fixing
build or runtime problems (if any) with their page table helpers.

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Steven Price <Steven.Price at arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Sri Krishna chowdary <schowdary at nvidia.com>
Cc: Dave Hansen <dave.hansen at intel.com>
Cc: Russell King - ARM Linux <linux at armlinux.org.uk>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Vineet Gupta <vgupta at synopsys.com>
Cc: James Hogan <jhogan at kernel.org>
Cc: Paul Burton <paul.burton at mips.com>
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: Kirill A. Shutemov <kirill at shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer at de.ibm.com>
Cc: Christophe Leroy <christophe.leroy at c-s.fr>
Cc: linux-snps-arc at lists.infradead.org
Cc: linux-mips at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-ia64 at vger.kernel.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: linux-s390 at vger.kernel.org
Cc: linux-sh at vger.kernel.org
Cc: sparclinux at vger.kernel.org
Cc: x86 at kernel.org
Cc: linux-kernel at vger.kernel.org

Tested-by: Christophe Leroy <christophe.leroy at c-s.fr>		#PPC32
Suggested-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 .../debug/debug-vm-pgtable/arch-support.txt        |  34 ++
 arch/arm64/Kconfig                                 |   1 +
 arch/x86/Kconfig                                   |   1 +
 arch/x86/include/asm/pgtable_64.h                  |   6 +
 include/asm-generic/pgtable.h                      |   6 +
 init/main.c                                        |   1 +
 lib/Kconfig.debug                                  |  21 +
 mm/Makefile                                        |   1 +
 mm/debug_vm_pgtable.c                              | 438 +++++++++++++++++++++
 9 files changed, 509 insertions(+)
 create mode 100644 Documentation/features/debug/debug-vm-pgtable/arch-support.txt
 create mode 100644 mm/debug_vm_pgtable.c

diff --git a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
new file mode 100644
index 0000000..d6b8185
--- /dev/null
+++ b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
@@ -0,0 +1,34 @@
+#
+# Feature name:          debug-vm-pgtable
+#         Kconfig:       ARCH_HAS_DEBUG_VM_PGTABLE
+#         description:   arch supports pgtable tests for semantics compliance
+#
+    -----------------------
+    |         arch |status|
+    -----------------------
+    |       alpha: | TODO |
+    |         arc: | TODO |
+    |         arm: | TODO |
+    |       arm64: |  ok  |
+    |         c6x: | TODO |
+    |        csky: | TODO |
+    |       h8300: | TODO |
+    |     hexagon: | TODO |
+    |        ia64: | TODO |
+    |        m68k: | TODO |
+    |  microblaze: | TODO |
+    |        mips: | TODO |
+    |       nds32: | TODO |
+    |       nios2: | TODO |
+    |    openrisc: | TODO |
+    |      parisc: | TODO |
+    |     powerpc: | TODO |
+    |       riscv: | TODO |
+    |        s390: | TODO |
+    |          sh: | TODO |
+    |       sparc: | TODO |
+    |          um: | TODO |
+    |   unicore32: | TODO |
+    |         x86: |  ok  |
+    |      xtensa: | TODO |
+    -----------------------
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 950a56b..8a3b3ea 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -11,6 +11,7 @@ config ARM64
 	select ACPI_PPTT if ACPI
 	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_DMA_COHERENT_TO_PFN
 	select ARCH_HAS_DMA_PREP_COHERENT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index abe822d..13c9bd9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -61,6 +61,7 @@ config X86
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 0b6c4042..fb0e76d 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -53,6 +53,12 @@ static inline void sync_initial_page_table(void) { }
 
 struct mm_struct;
 
+#define mm_p4d_folded mm_p4d_folded
+static inline bool mm_p4d_folded(struct mm_struct *mm)
+{
+	return !pgtable_l5_enabled();
+}
+
 void set_pte_vaddr_p4d(p4d_t *p4d_page, unsigned long vaddr, pte_t new_pte);
 void set_pte_vaddr_pud(pud_t *pud_page, unsigned long vaddr, pte_t new_pte);
 
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 8186918..9e5c248 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1187,4 +1187,10 @@ static inline bool arch_has_pfn_modify_check(void)
 #define mm_pmd_folded(mm)	__is_defined(__PAGETABLE_PMD_FOLDED)
 #endif
 
+#ifdef CONFIG_DEBUG_VM_PGTABLE
+extern void debug_vm_pgtable(void);
+#else
+static inline void debug_vm_pgtable(void) { }
+#endif
+
 #endif /* _ASM_GENERIC_PGTABLE_H */
diff --git a/init/main.c b/init/main.c
index 91f6ebb..676d8020 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1177,6 +1177,7 @@ static noinline void __init kernel_init_freeable(void)
 	workqueue_init();
 
 	init_mm_internals();
+	debug_vm_pgtable();
 
 	do_pre_smp_initcalls();
 	lockup_detector_init();
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cb1fc48..b9b8fe1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -698,6 +698,27 @@ config DEBUG_VM_PGFLAGS
 
 	  If unsure, say N.
 
+config ARCH_HAS_DEBUG_VM_PGTABLE
+	bool
+	help
+	  An architecture should select this when it can successfully
+	  build and run DEBUG_VM_PGTABLE.
+
+config DEBUG_VM_PGTABLE
+	bool "Debug arch page table for semantics compliance"
+	depends on MMU
+	depends on DEBUG_VM
+	depends on ARCH_HAS_DEBUG_VM_PGTABLE
+	help
+	  This option provides a debug method which can be used to test
+	  architecture page table helper functions on various platforms in
+	  verifying if they comply with expected generic MM semantics. This
+	  will help architecture code in making sure that any changes or
+	  new additions of these helpers still conform to expected
+	  semantics of the generic MM.
+
+	  If unsure, say N.
+
 config ARCH_HAS_DEBUG_VIRTUAL
 	bool
 
diff --git a/mm/Makefile b/mm/Makefile
index d996846..2f085b9 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -86,6 +86,7 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
 obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
+obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
 obj-$(CONFIG_PAGE_OWNER) += page_owner.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
new file mode 100644
index 0000000..885d1e5
--- /dev/null
+++ b/mm/debug_vm_pgtable.c
@@ -0,0 +1,438 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This kernel module validates architecture page table helpers &
+ * accessors and helps in verifying their continued compliance with
+ * generic MM semantics.
+ *
+ * Copyright (C) 2019 ARM Ltd.
+ *
+ * Author: Anshuman Khandual <anshuman.khandual at arm.com>
+ */
+#define pr_fmt(fmt) "arch_pgtable_test: %s " fmt, __func__
+
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/hugetlb.h>
+#include <linux/kernel.h>
+#include <linux/kconfig.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mm_types.h>
+#include <linux/module.h>
+#include <linux/pfn_t.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/spinlock.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/sched/mm.h>
+#include <asm/pgalloc.h>
+#include <asm/pgtable.h>
+
+/*
+ * Basic operations
+ *
+ * mkold(entry)			= An old and not a young entry
+ * mkyoung(entry)		= A young and not an old entry
+ * mkdirty(entry)		= A dirty and not a clean entry
+ * mkclean(entry)		= A clean and not a dirty entry
+ * mkwrite(entry)		= A write and not a write protected entry
+ * wrprotect(entry)		= A write protected and not a write entry
+ * pxx_bad(entry)		= A mapped and non-table entry
+ * pxx_same(entry1, entry2)	= Both entries hold the exact same value
+ */
+#define VMFLAGS	(VM_READ|VM_WRITE|VM_EXEC)
+
+/*
+ * On s390 platform, the lower 12 bits are used to identify given page table
+ * entry type and for other arch specific requirements. But these bits might
+ * affect the ability to clear entries with pxx_clear(). So while loading up
+ * the entries skip all lower 12 bits in order to accommodate s390 platform.
+ * It does not have affect any other platform.
+ */
+#define RANDOM_ORVALUE	(0xfffffffffffff000UL)
+#define RANDOM_NZVALUE	(0xff)
+
+static bool pud_aligned __initdata;
+static bool pmd_aligned __initdata;
+
+static void __init pte_basic_tests(struct page *page, pgprot_t prot)
+{
+	pte_t pte = mk_pte(page, prot);
+
+	WARN_ON(!pte_same(pte, pte));
+	WARN_ON(!pte_young(pte_mkyoung(pte)));
+	WARN_ON(!pte_dirty(pte_mkdirty(pte)));
+	WARN_ON(!pte_write(pte_mkwrite(pte)));
+	WARN_ON(pte_young(pte_mkold(pte)));
+	WARN_ON(pte_dirty(pte_mkclean(pte)));
+	WARN_ON(pte_write(pte_wrprotect(pte)));
+}
+
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE
+static void __init pmd_basic_tests(struct page *page, pgprot_t prot)
+{
+	pmd_t pmd;
+
+	/*
+	 * Memory block here must be PMD_SIZE aligned. Abort this
+	 * test in case we could not allocate such a memory block.
+	 */
+	if (!pmd_aligned) {
+		pr_warn("Could not proceed with PMD tests\n");
+		return;
+	}
+
+	pmd = mk_pmd(page, prot);
+	WARN_ON(!pmd_same(pmd, pmd));
+	WARN_ON(!pmd_young(pmd_mkyoung(pmd)));
+	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd)));
+	WARN_ON(!pmd_write(pmd_mkwrite(pmd)));
+	WARN_ON(pmd_young(pmd_mkold(pmd)));
+	WARN_ON(pmd_dirty(pmd_mkclean(pmd)));
+	WARN_ON(pmd_write(pmd_wrprotect(pmd)));
+	/*
+	 * A huge page does not point to next level page table
+	 * entry. Hence this must qualify as pmd_bad().
+	 */
+	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
+}
+#else
+static void __init pmd_basic_tests(struct page *page, pgprot_t prot) { }
+#endif
+
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+static void __init pud_basic_tests(struct page *page, pgprot_t prot)
+{
+	pud_t pud;
+
+	/*
+	 * Memory block here must be PUD_SIZE aligned. Abort this
+	 * test in case we could not allocate such a memory block.
+	 */
+	if (!pud_aligned) {
+		pr_warn("Could not proceed with PUD tests\n");
+		return;
+	}
+
+	pud = pfn_pud(page_to_pfn(page), prot);
+	WARN_ON(!pud_same(pud, pud));
+	WARN_ON(!pud_young(pud_mkyoung(pud)));
+	WARN_ON(!pud_write(pud_mkwrite(pud)));
+	WARN_ON(pud_write(pud_wrprotect(pud)));
+	WARN_ON(pud_young(pud_mkold(pud)));
+
+	if (mm_pmd_folded(mm) || __is_defined(ARCH_HAS_4LEVEL_HACK))
+		return;
+
+	/*
+	 * A huge page does not point to next level page table
+	 * entry. Hence this must qualify as pud_bad().
+	 */
+	WARN_ON(!pud_bad(pud_mkhuge(pud)));
+}
+#else
+static void __init pud_basic_tests(struct page *page, pgprot_t prot) { }
+#endif
+
+static void __init p4d_basic_tests(struct page *page, pgprot_t prot)
+{
+	p4d_t p4d;
+
+	memset(&p4d, RANDOM_NZVALUE, sizeof(p4d_t));
+	WARN_ON(!p4d_same(p4d, p4d));
+}
+
+static void __init pgd_basic_tests(struct page *page, pgprot_t prot)
+{
+	pgd_t pgd;
+
+	memset(&pgd, RANDOM_NZVALUE, sizeof(pgd_t));
+	WARN_ON(!pgd_same(pgd, pgd));
+}
+
+#ifndef __ARCH_HAS_4LEVEL_HACK
+static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp)
+{
+	pud_t pud = READ_ONCE(*pudp);
+
+	if (mm_pmd_folded(mm))
+		return;
+
+	pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pudp, pud);
+	pud_clear(pudp);
+	pud = READ_ONCE(*pudp);
+	WARN_ON(!pud_none(pud));
+}
+
+static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
+				      pmd_t *pmdp)
+{
+	pud_t pud;
+
+	if (mm_pmd_folded(mm))
+		return;
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pud_bad().
+	 */
+	pmd_clear(pmdp);
+	pud_clear(pudp);
+	pud_populate(mm, pudp, pmdp);
+	pud = READ_ONCE(*pudp);
+	WARN_ON(pud_bad(pud));
+}
+#else
+static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp) { }
+static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
+				      pmd_t *pmdp)
+{
+}
+#endif
+
+#ifndef __ARCH_HAS_5LEVEL_HACK
+static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp)
+{
+	p4d_t p4d = READ_ONCE(*p4dp);
+
+	if (mm_pud_folded(mm))
+		return;
+
+	p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE);
+	WRITE_ONCE(*p4dp, p4d);
+	p4d_clear(p4dp);
+	p4d = READ_ONCE(*p4dp);
+	WARN_ON(!p4d_none(p4d));
+}
+
+static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
+				      pud_t *pudp)
+{
+	p4d_t p4d;
+
+	if (mm_pud_folded(mm))
+		return;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as p4d_bad().
+	 */
+	pud_clear(pudp);
+	p4d_clear(p4dp);
+	p4d_populate(mm, p4dp, pudp);
+	p4d = READ_ONCE(*p4dp);
+	WARN_ON(p4d_bad(p4d));
+}
+
+static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp)
+{
+	pgd_t pgd = READ_ONCE(*pgdp);
+
+	if (mm_p4d_folded(mm))
+		return;
+
+	pgd = __pgd(pgd_val(pgd) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pgdp, pgd);
+	pgd_clear(pgdp);
+	pgd = READ_ONCE(*pgdp);
+	WARN_ON(!pgd_none(pgd));
+}
+
+static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
+				      p4d_t *p4dp)
+{
+	pgd_t pgd;
+
+	if (mm_p4d_folded(mm))
+		return;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pgd_bad().
+	 */
+	p4d_clear(p4dp);
+	pgd_clear(pgdp);
+	pgd_populate(mm, pgdp, p4dp);
+	pgd = READ_ONCE(*pgdp);
+	WARN_ON(pgd_bad(pgd));
+}
+#else
+static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp) { }
+static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp) { }
+static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
+				      pud_t *pudp)
+{
+}
+static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
+				      p4d_t *p4dp)
+{
+}
+#endif
+
+static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
+{
+	pte_t pte = READ_ONCE(*ptep);
+
+	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
+	WRITE_ONCE(*ptep, pte);
+	pte_clear(mm, 0, ptep);
+	pte = READ_ONCE(*ptep);
+	WARN_ON(!pte_none(pte));
+}
+
+static void __init pmd_clear_tests(struct mm_struct *mm, pmd_t *pmdp)
+{
+	pmd_t pmd = READ_ONCE(*pmdp);
+
+	pmd = __pmd(pmd_val(pmd) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pmdp, pmd);
+	pmd_clear(pmdp);
+	pmd = READ_ONCE(*pmdp);
+	WARN_ON(!pmd_none(pmd));
+}
+
+static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
+				      pgtable_t pgtable)
+{
+	pmd_t pmd;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pmd_bad().
+	 */
+	pmd_clear(pmdp);
+	pmd_populate(mm, pmdp, pgtable);
+	pmd = READ_ONCE(*pmdp);
+	WARN_ON(pmd_bad(pmd));
+}
+
+static struct page * __init alloc_mapped_page(void)
+{
+	struct page *page;
+	gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
+
+	page = alloc_gigantic_page_order(get_order(PUD_SIZE), gfp_mask,
+				first_memory_node, &node_states[N_MEMORY]);
+	if (page) {
+		pud_aligned = true;
+		pmd_aligned = true;
+		return page;
+	}
+
+	page = alloc_pages(gfp_mask, get_order(PMD_SIZE));
+	if (page) {
+		pmd_aligned = true;
+		return page;
+	}
+	return alloc_page(gfp_mask);
+}
+
+static void __init free_mapped_page(struct page *page)
+{
+	if (pud_aligned) {
+		unsigned long pfn = page_to_pfn(page);
+
+		free_contig_range(pfn, 1ULL << get_order(PUD_SIZE));
+		return;
+	}
+
+	if (pmd_aligned) {
+		int order = get_order(PMD_SIZE);
+
+		free_pages((unsigned long)page_address(page), order);
+		return;
+	}
+	free_page((unsigned long)page_address(page));
+}
+
+static unsigned long __init get_random_vaddr(void)
+{
+	unsigned long random_vaddr, random_pages, total_user_pages;
+
+	total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE;
+
+	random_pages = get_random_long() % total_user_pages;
+	random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE;
+
+	WARN_ON(random_vaddr > TASK_SIZE);
+	WARN_ON(random_vaddr < FIRST_USER_ADDRESS);
+	return random_vaddr;
+}
+
+void __init debug_vm_pgtable(void)
+{
+	struct mm_struct *mm;
+	struct page *page;
+	pgd_t *pgdp;
+	p4d_t *p4dp, *saved_p4dp;
+	pud_t *pudp, *saved_pudp;
+	pmd_t *pmdp, *saved_pmdp, pmd;
+	pte_t *ptep;
+	pgtable_t saved_ptep;
+	pgprot_t prot;
+	unsigned long vaddr;
+
+	prot = vm_get_page_prot(VMFLAGS);
+	vaddr = get_random_vaddr();
+	mm = mm_alloc();
+	if (!mm) {
+		pr_err("mm_struct allocation failed\n");
+		return;
+	}
+
+	page = alloc_mapped_page();
+	if (!page) {
+		pr_err("memory allocation failed\n");
+		return;
+	}
+
+	pgdp = pgd_offset(mm, vaddr);
+	p4dp = p4d_alloc(mm, pgdp, vaddr);
+	pudp = pud_alloc(mm, p4dp, vaddr);
+	pmdp = pmd_alloc(mm, pudp, vaddr);
+	ptep = pte_alloc_map(mm, pmdp, vaddr);
+
+	/*
+	 * Save all the page table page addresses as the page table
+	 * entries will be used for testing with random or garbage
+	 * values. These saved addresses will be used for freeing
+	 * page table pages.
+	 */
+	pmd = READ_ONCE(*pmdp);
+	saved_p4dp = p4d_offset(pgdp, 0UL);
+	saved_pudp = pud_offset(p4dp, 0UL);
+	saved_pmdp = pmd_offset(pudp, 0UL);
+	saved_ptep = pmd_pgtable(pmd);
+
+	pte_basic_tests(page, prot);
+	pmd_basic_tests(page, prot);
+	pud_basic_tests(page, prot);
+	p4d_basic_tests(page, prot);
+	pgd_basic_tests(page, prot);
+
+	pte_clear_tests(mm, ptep);
+	pmd_clear_tests(mm, pmdp);
+	pud_clear_tests(mm, pudp);
+	p4d_clear_tests(mm, p4dp);
+	pgd_clear_tests(mm, pgdp);
+
+	pte_unmap(ptep);
+
+	pmd_populate_tests(mm, pmdp, saved_ptep);
+	pud_populate_tests(mm, pudp, saved_pmdp);
+	p4d_populate_tests(mm, p4dp, saved_pudp);
+	pgd_populate_tests(mm, pgdp, saved_p4dp);
+
+	p4d_free(mm, saved_p4dp);
+	pud_free(mm, saved_pudp);
+	pmd_free(mm, saved_pmdp);
+	pte_free(mm, saved_ptep);
+
+	mm_dec_nr_puds(mm);
+	mm_dec_nr_pmds(mm);
+	mm_dec_nr_ptes(mm);
+	__mmdrop(mm);
+
+	free_mapped_page(page);
+}
-- 
2.7.4