[PATCH V4 0/2] mm/debug: Add tests for architecture exported page table helpers

[PATCH V4 0/2] mm/debug: Add tests for architecture exported 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@arrakis.emea.arm.com/

Changes in V4:

- 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@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@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@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@arm.com/

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

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

 arch/x86/include/asm/pgtable_64_types.h |   2 +
 include/linux/hugetlb.h                 |   9 +
 mm/Kconfig.debug                        |  15 +
 mm/Makefile                             |   1 +
 mm/arch_pgtable_test.c                  | 440 ++++++++++++++++++++++++
 mm/hugetlb.c                            |  24 +-
 6 files changed, 489 insertions(+), 2 deletions(-)
 create mode 100644 mm/arch_pgtable_test.c

-- 
2.20.1

[PATCH V4 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@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Steven Price <Steven.Price@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sri Krishna chowdary <schowdary@nvidia.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-mips@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-ia64@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@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 53fc34f930d0..cc50d5ad4885 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -299,6 +299,9 @@ 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
@@ -310,6 +313,12 @@ 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 ef37c85423a5..3fb81252f52b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1112,10 +1112,9 @@ 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;
@@ -1151,6 +1150,14 @@ 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 */
@@ -1159,6 +1166,12 @@ 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 */
@@ -1167,6 +1180,13 @@ 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) { }
-- 
2.20.1

[PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Anshuman Khandual]

This adds a test module which will validate architecture page table helpers
and accessors regarding compliance with generic MM semantics expectations.
This will help various architectures in validating changes to the 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 alignments. If memory pages
with required size and alignment could not be allocated, then all depending
individual tests are skipped.

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

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>		#PPC32
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/x86/include/asm/pgtable_64_types.h |   2 +
 mm/Kconfig.debug                        |  15 +
 mm/Makefile                             |   1 +
 mm/arch_pgtable_test.c                  | 440 ++++++++++++++++++++++++
 4 files changed, 458 insertions(+)
 create mode 100644 mm/arch_pgtable_test.c

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 52e5f5f2240d..b882792a3999 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
 #define pgtable_l5_enabled() 0
 #endif /* CONFIG_X86_5LEVEL */
 
+#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
+
 extern unsigned int pgdir_shift;
 extern unsigned int ptrs_per_p4d;
 
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 327b3ebf23bf..683131b1ee7d 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -117,3 +117,18 @@ config DEBUG_RODATA_TEST
     depends on STRICT_KERNEL_RWX
     ---help---
       This option enables a testcase for the setting rodata read-only.
+
+config DEBUG_ARCH_PGTABLE_TEST
+	bool "Test arch page table helpers for semantics compliance"
+	depends on MMU
+	depends on DEBUG_KERNEL
+	depends on !(ARM || IA64)
+	help
+	  This options provides a kernel module which can be used to test
+	  architecture page table helper functions on various platform in
+	  verifying if they comply with expected generic MM semantics. This
+	  will help architectures code in making sure that any changes or
+	  new additions of these helpers will still conform to generic MM
+	  expected semantics.
+
+	  If unsure, say N.
diff --git a/mm/Makefile b/mm/Makefile
index d996846697ef..bb572c5aa8c5 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-$(CONFIG_DEBUG_ARCH_PGTABLE_TEST) += arch_pgtable_test.o
 obj-$(CONFIG_PAGE_OWNER) += page_owner.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/arch_pgtable_test.c b/mm/arch_pgtable_test.c
new file mode 100644
index 000000000000..2942a0484d63
--- /dev/null
+++ b/mm/arch_pgtable_test.c
@@ -0,0 +1,440 @@
+// 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@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;
+}
+
+static int __init arch_pgtable_tests_init(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 1;
+	}
+
+	page = alloc_mapped_page();
+	if (!page) {
+		pr_err("memory allocation failed\n");
+		return 1;
+	}
+
+	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);
+	return 0;
+}
+late_initcall(arch_pgtable_tests_init);
-- 
2.20.1

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Ingo Molnar]

* Anshuman Khandual <anshuman.khandual@arm.com> wrote:

> This adds a test module which will validate architecture page table helpers
> and accessors regarding compliance with generic MM semantics expectations.
> This will help various architectures in validating changes to the 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 alignments. If memory pages
> with required size and alignment could not be allocated, then all depending
> individual tests are skipped.

> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 52e5f5f2240d..b882792a3999 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
>  #define pgtable_l5_enabled() 0
>  #endif /* CONFIG_X86_5LEVEL */
>  
> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> +
>  extern unsigned int pgdir_shift;
>  extern unsigned int ptrs_per_p4d;

Any deep reason this has to be a macro instead of proper C?

> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 327b3ebf23bf..683131b1ee7d 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -117,3 +117,18 @@ config DEBUG_RODATA_TEST
>      depends on STRICT_KERNEL_RWX
>      ---help---
>        This option enables a testcase for the setting rodata read-only.
> +
> +config DEBUG_ARCH_PGTABLE_TEST
> +	bool "Test arch page table helpers for semantics compliance"
> +	depends on MMU
> +	depends on DEBUG_KERNEL
> +	depends on !(ARM || IA64)

Please add a proper enabling switch for architectures to opt in.

Please also add it to Documentation/features/list-arch.sh so that it's 
listed as a 'TODO' entry on architectures where the tests are not enabled 
yet.

> +	help
> +	  This options provides a kernel module which can be used to test
> +	  architecture page table helper functions on various platform in
> +	  verifying if they comply with expected generic MM semantics. This
> +	  will help architectures code in making sure that any changes or
> +	  new additions of these helpers will still conform to generic MM
> +	  expected semantics.

Typos and grammar fixed:

	help
	  This option provides a kernel module 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.

Also, more fundamentally: isn't a kernel module too late for such a debug 
check, should something break due to a core MM change? Have these debug 
checks caught any bugs or inconsistencies before?

Why not call this as some earlier MM debug check, after enabling paging 
but before executing user-space binaries or relying on complex MM ops 
within the kernel, called at a stage when those primitives are all 
expected to work fine?

It seems to me that arch_pgtable_tests_init) won't even context-switch 
normally, right?

Finally, instead of inventing yet another randomly named .config debug 
switch, please fit it into the regular MM debug options which go along 
the CONFIG_DEBUG_VM* naming scheme.

Might even make sense to enable these new debug checks by default if 
CONFIG_DEBUG_VM=y, that way we'll get a *lot* more debug coverage than 
some random module somewhere that few people will know about, let alone 
run.

Thanks,

	Ingo

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Kirill A. Shutemov]

On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> 
> * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
> > This adds a test module which will validate architecture page table helpers
> > and accessors regarding compliance with generic MM semantics expectations.
> > This will help various architectures in validating changes to the 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 alignments. If memory pages
> > with required size and alignment could not be allocated, then all depending
> > individual tests are skipped.
> 
> > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> > index 52e5f5f2240d..b882792a3999 100644
> > --- a/arch/x86/include/asm/pgtable_64_types.h
> > +++ b/arch/x86/include/asm/pgtable_64_types.h
> > @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
> >  #define pgtable_l5_enabled() 0
> >  #endif /* CONFIG_X86_5LEVEL */
> >  
> > +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> > +
> >  extern unsigned int pgdir_shift;
> >  extern unsigned int ptrs_per_p4d;
> 
> Any deep reason this has to be a macro instead of proper C?

It's a way to override the generic mm_p4d_folded(). It can be rewritten
as inline function + define. Something like:

#define mm_p4d_folded mm_p4d_folded
static inline bool mm_p4d_folded(struct mm_struct *mm)
{
	return !pgtable_l5_enabled();
}

But I don't see much reason to be more verbose here than needed.

-- 
 Kirill A. Shutemov

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Ingo Molnar]

* Kirill A. Shutemov <kirill@shutemov.name> wrote:

> On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> > 
> > * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> > 
> > > This adds a test module which will validate architecture page table helpers
> > > and accessors regarding compliance with generic MM semantics expectations.
> > > This will help various architectures in validating changes to the 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 alignments. If memory pages
> > > with required size and alignment could not be allocated, then all depending
> > > individual tests are skipped.
> > 
> > > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> > > index 52e5f5f2240d..b882792a3999 100644
> > > --- a/arch/x86/include/asm/pgtable_64_types.h
> > > +++ b/arch/x86/include/asm/pgtable_64_types.h
> > > @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
> > >  #define pgtable_l5_enabled() 0
> > >  #endif /* CONFIG_X86_5LEVEL */
> > >  
> > > +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> > > +
> > >  extern unsigned int pgdir_shift;
> > >  extern unsigned int ptrs_per_p4d;
> > 
> > Any deep reason this has to be a macro instead of proper C?
> 
> It's a way to override the generic mm_p4d_folded(). It can be rewritten
> as inline function + define. Something like:
> 
> #define mm_p4d_folded mm_p4d_folded
> static inline bool mm_p4d_folded(struct mm_struct *mm)
> {
> 	return !pgtable_l5_enabled();
> }
> 
> But I don't see much reason to be more verbose here than needed.

C type checking? Documentation? Yeah, I know it's just a one-liner, but 
the principle of the death by a thousand cuts applies here.

BTW., any reason this must be in the low level pgtable_64_types.h type 
header, instead of one of the API level header files?

Thanks,

	Ingo

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Kirill A. Shutemov]

On Mon, Oct 07, 2019 at 03:51:58PM +0200, Ingo Molnar wrote:
> 
> * Kirill A. Shutemov <kirill@shutemov.name> wrote:
> 
> > On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> > > 
> > > * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> > > 
> > > > This adds a test module which will validate architecture page table helpers
> > > > and accessors regarding compliance with generic MM semantics expectations.
> > > > This will help various architectures in validating changes to the 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 alignments. If memory pages
> > > > with required size and alignment could not be allocated, then all depending
> > > > individual tests are skipped.
> > > 
> > > > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> > > > index 52e5f5f2240d..b882792a3999 100644
> > > > --- a/arch/x86/include/asm/pgtable_64_types.h
> > > > +++ b/arch/x86/include/asm/pgtable_64_types.h
> > > > @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
> > > >  #define pgtable_l5_enabled() 0
> > > >  #endif /* CONFIG_X86_5LEVEL */
> > > >  
> > > > +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> > > > +
> > > >  extern unsigned int pgdir_shift;
> > > >  extern unsigned int ptrs_per_p4d;
> > > 
> > > Any deep reason this has to be a macro instead of proper C?
> > 
> > It's a way to override the generic mm_p4d_folded(). It can be rewritten
> > as inline function + define. Something like:
> > 
> > #define mm_p4d_folded mm_p4d_folded
> > static inline bool mm_p4d_folded(struct mm_struct *mm)
> > {
> > 	return !pgtable_l5_enabled();
> > }
> > 
> > But I don't see much reason to be more verbose here than needed.
> 
> C type checking? Documentation? Yeah, I know it's just a one-liner, but 
> the principle of the death by a thousand cuts applies here.

Okay, if you think it worth it. Anshuman, could you fix it up for the next
submission?


> BTW., any reason this must be in the low level pgtable_64_types.h type 
> header, instead of one of the API level header files?

I defined it next pgtable_l5_enabled(). What is more appropriate place to
you? pgtable_64.h? Yeah, it makes sense.

-- 
 Kirill A. Shutemov

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Anshuman Khandual]

On 10/07/2019 07:30 PM, Kirill A. Shutemov wrote:
> On Mon, Oct 07, 2019 at 03:51:58PM +0200, Ingo Molnar wrote:
>>
>> * Kirill A. Shutemov <kirill@shutemov.name> wrote:
>>
>>> On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
>>>>
>>>> * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>>>
>>>>> This adds a test module which will validate architecture page table helpers
>>>>> and accessors regarding compliance with generic MM semantics expectations.
>>>>> This will help various architectures in validating changes to the 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 alignments. If memory pages
>>>>> with required size and alignment could not be allocated, then all depending
>>>>> individual tests are skipped.
>>>>
>>>>> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
>>>>> index 52e5f5f2240d..b882792a3999 100644
>>>>> --- a/arch/x86/include/asm/pgtable_64_types.h
>>>>> +++ b/arch/x86/include/asm/pgtable_64_types.h
>>>>> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
>>>>>  #define pgtable_l5_enabled() 0
>>>>>  #endif /* CONFIG_X86_5LEVEL */
>>>>>  
>>>>> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
>>>>> +
>>>>>  extern unsigned int pgdir_shift;
>>>>>  extern unsigned int ptrs_per_p4d;
>>>>
>>>> Any deep reason this has to be a macro instead of proper C?
>>>
>>> It's a way to override the generic mm_p4d_folded(). It can be rewritten
>>> as inline function + define. Something like:
>>>
>>> #define mm_p4d_folded mm_p4d_folded
>>> static inline bool mm_p4d_folded(struct mm_struct *mm)
>>> {
>>> 	return !pgtable_l5_enabled();
>>> }
>>>
>>> But I don't see much reason to be more verbose here than needed.
>>
>> C type checking? Documentation? Yeah, I know it's just a one-liner, but 
>> the principle of the death by a thousand cuts applies here.
> 
> Okay, if you think it worth it. Anshuman, could you fix it up for the next
> submission?

Sure, will do.

> 
> 
>> BTW., any reason this must be in the low level pgtable_64_types.h type 
>> header, instead of one of the API level header files?
> 
> I defined it next pgtable_l5_enabled(). What is more appropriate place to
> you? pgtable_64.h? Yeah, it makes sense.


Needs to be moved to arch/x86/include/asm/pgtable_64.h as well ?

Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

[Anshuman Khandual]

On 10/07/2019 06:36 PM, Ingo Molnar wrote:
> 
> * Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
>> This adds a test module which will validate architecture page table helpers
>> and accessors regarding compliance with generic MM semantics expectations.
>> This will help various architectures in validating changes to the 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 alignments. If memory pages
>> with required size and alignment could not be allocated, then all depending
>> individual tests are skipped.
> 
>> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
>> index 52e5f5f2240d..b882792a3999 100644
>> --- a/arch/x86/include/asm/pgtable_64_types.h
>> +++ b/arch/x86/include/asm/pgtable_64_types.h
>> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
>>  #define pgtable_l5_enabled() 0
>>  #endif /* CONFIG_X86_5LEVEL */
>>  
>> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
>> +
>>  extern unsigned int pgdir_shift;
>>  extern unsigned int ptrs_per_p4d;
> 
> Any deep reason this has to be a macro instead of proper C?
> 
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 327b3ebf23bf..683131b1ee7d 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -117,3 +117,18 @@ config DEBUG_RODATA_TEST
>>      depends on STRICT_KERNEL_RWX
>>      ---help---
>>        This option enables a testcase for the setting rodata read-only.
>> +
>> +config DEBUG_ARCH_PGTABLE_TEST
>> +	bool "Test arch page table helpers for semantics compliance"
>> +	depends on MMU
>> +	depends on DEBUG_KERNEL
>> +	depends on !(ARM || IA64)
> 
> Please add a proper enabling switch for architectures to opt in.

Sure, will do.

> 
> Please also add it to Documentation/features/list-arch.sh so that it's 
> listed as a 'TODO' entry on architectures where the tests are not enabled 
> yet.

Will do.

> 
>> +	help
>> +	  This options provides a kernel module which can be used to test
>> +	  architecture page table helper functions on various platform in
>> +	  verifying if they comply with expected generic MM semantics. This
>> +	  will help architectures code in making sure that any changes or
>> +	  new additions of these helpers will still conform to generic MM
>> +	  expected semantics.
> 
> Typos and grammar fixed:
> 
> 	help
> 	  This option provides a kernel module 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.

Sure, will update except the 'kernel module' part. Thank you.

> 
> Also, more fundamentally: isn't a kernel module too late for such a debug

Its not a kernel module any more, my bad that the description has still these
words left on from previous versions, will fix it. The test now gets invoked
through a late_initcall().

> check, should something break due to a core MM change? Have these debug 
> checks caught any bugs or inconsistencies before?

Gerald Schaefer had reported earlier about a bug found on s390 with this test.

https://lkml.org/lkml/2019/9/4/1718

> 
> Why not call this as some earlier MM debug check, after enabling paging 
> but before executing user-space binaries or relying on complex MM ops 
> within the kernel, called at a stage when those primitives are all 
> expected to work fine?

At minimum we need buddy allocator to be initialized for the allocations to
work. Just after pgtable_init() or kmem_cache_init() in mm_init() will be a
good place ?

> 
> It seems to me that arch_pgtable_tests_init) won't even context-switch 
> normally, right?

Not sure whether I got this. Why would you expect it to context switch ?

> 
> Finally, instead of inventing yet another randomly named .config debug 
> switch, please fit it into the regular MM debug options which go along 
> the CONFIG_DEBUG_VM* naming scheme.
> 
> Might even make sense to enable these new debug checks by default if 
> CONFIG_DEBUG_VM=y, that way we'll get a *lot* more debug coverage than 
> some random module somewhere that few people will know about, let alone 
> run.

All the configs with respect to memory debugging is generated from
lib/Kconfig.debug after fetching all that is in "mm/Kconfig.debug".
There are only three configs which depend on CONFIG_DEBUG_VM like
a package.

1. CONFIG_DEBUG_VM_VMACACHE
2. CONFIG_DEBUG_VM_RB
3. CONFIG_DEBUG_VM_PGFLAGS
4. CONFIG_DEBUG_VM_PGTABLE [proposed for this]

Before that, just trying to understand whether the reason of making this
arch page table test as part of DEBUG_VM_* package than a just a stand
alone config as many others, is that it is directly related to virtual
memory enablement in kernel. Or is there something else I am missing.

But this looks better and will make this depend on a selectable arch
config like ARCH_HAS_DEBUG_VM_PGTABLE or something.

> 
> Thanks,
> 
> 	Ingo
>