Re: [PATCH 1/1] mm/pgtable/debug: Add test validating architecture page table helpers

[Kirill A. Shutemov]

On Tue, Sep 03, 2019 at 01:31:46PM +0530, Anshuman Khandual 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.

See my comments below.

> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Steven Price <Steven.Price@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Sri Krishna chowdary <schowdary@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> Cc: James Hogan <jhogan@xxxxxxxxxx>
> Cc: Paul Burton <paul.burton@xxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Cc: linux-snps-arc@xxxxxxxxxxxxxxxxxxx
> Cc: linux-mips@xxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-ia64@xxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-s390@xxxxxxxxxxxxxxx
> Cc: linux-sh@xxxxxxxxxxxxxxx
> Cc: sparclinux@xxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  mm/Kconfig.debug       |  14 ++
>  mm/Makefile            |   1 +
>  mm/arch_pgtable_test.c | 425 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 440 insertions(+)
>  create mode 100644 mm/arch_pgtable_test.c
> 
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 327b3ebf23bf..ce9c397f7b07 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -117,3 +117,17 @@ 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
> +	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..f15be8a73723
> --- /dev/null
> +++ b/mm/arch_pgtable_test.c
> @@ -0,0 +1,425 @@
> +// 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@xxxxxxx>
> + */
> +#define pr_fmt(fmt) "arch_pgtable_test: %s " fmt, __func__
> +
> +#include <linux/kernel.h>
> +#include <linux/hugetlb.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/mm_types.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +#include <linux/pfn_t.h>
> +#include <linux/gfp.h>
> +#include <linux/spinlock.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 VADDR_TEST	(PGDIR_SIZE + PUD_SIZE + PMD_SIZE + PAGE_SIZE)

What is special about this address? How do you know if it is not occupied
yet?

> +#define VMA_TEST_FLAGS	(VM_READ|VM_WRITE|VM_EXEC)
> +#define RANDOM_NZVALUE	(0xbe)
> +
> +static bool pud_aligned;
> +static bool pmd_aligned;
> +
> +extern struct mm_struct *mm_alloc(void);
> +
> +static void 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 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 pmd_basic_tests(struct page *page, pgprot_t prot) { }
> +#endif
> +
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> +static void 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 !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
> +	/*
> +	 * 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)));
> +#endif
> +}
> +#else
> +static void pud_basic_tests(struct page *page, pgprot_t prot) { }
> +#endif
> +
> +static void 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 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));
> +}
> +
> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
> +static void pud_clear_tests(pud_t *pudp)
> +{
> +	memset(pudp, RANDOM_NZVALUE, sizeof(pud_t));
> +	pud_clear(pudp);
> +	WARN_ON(!pud_none(READ_ONCE(*pudp)));
> +}
> +
> +static void pud_populate_tests(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
> +{
> +	/*
> +	 * 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);
> +	WARN_ON(pud_bad(READ_ONCE(*pudp)));
> +}
> +#else
> +static void pud_clear_tests(pud_t *pudp) { }
> +static void pud_populate_tests(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
> +{
> +}
> +#endif
> +
> +#if !defined(__PAGETABLE_PUD_FOLDED) && !defined(__ARCH_HAS_5LEVEL_HACK)
> +static void p4d_clear_tests(p4d_t *p4dp)
> +{
> +	memset(p4dp, RANDOM_NZVALUE, sizeof(p4d_t));
> +	p4d_clear(p4dp);
> +	WARN_ON(!p4d_none(READ_ONCE(*p4dp)));
> +}
> +
> +static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
> +{
> +	/*
> +	 * 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);
> +	WARN_ON(p4d_bad(READ_ONCE(*p4dp)));
> +}
> +#else
> +static void p4d_clear_tests(p4d_t *p4dp) { }
> +static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
> +{
> +}
> +#endif
> +
> +#ifndef __PAGETABLE_P4D_FOLDED
> +static void pgd_clear_tests(pgd_t *pgdp)
> +{
> +	memset(pgdp, RANDOM_NZVALUE, sizeof(pgd_t));
> +	pgd_clear(pgdp);
> +	WARN_ON(!pgd_none(READ_ONCE(*pgdp)));
> +}
> +
> +static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
> +{
> +	/*
> +	 * 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);
> +	WARN_ON(pgd_bad(READ_ONCE(*pgdp)));
> +}
> +#else
> +static void pgd_clear_tests(pgd_t *pgdp) { }
> +static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
> +{
> +}
> +#endif

This will not work if p4d is folded at runtime. Like for x86-64 and s390.

Here's the fixup. It should work for both x86-64 and s390, but I only
tested on x86-64:

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/arch_pgtable_test.c b/mm/arch_pgtable_test.c
index f15be8a73723..206fe3334a28 100644
--- a/mm/arch_pgtable_test.c
+++ b/mm/arch_pgtable_test.c
@@ -193,9 +193,11 @@ static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
 }
 #endif
 
-#ifndef __PAGETABLE_P4D_FOLDED
 static void pgd_clear_tests(pgd_t *pgdp)
 {
+	if (mm_p4d_folded(mm))
+		return;
+
 	memset(pgdp, RANDOM_NZVALUE, sizeof(pgd_t));
 	pgd_clear(pgdp);
 	WARN_ON(!pgd_none(READ_ONCE(*pgdp)));
@@ -203,6 +205,9 @@ static void pgd_clear_tests(pgd_t *pgdp)
 
 static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
 {
+	if (mm_p4d_folded(mm))
+		return;
+
 	/*
 	 * This entry points to next level page table page.
 	 * Hence this must not qualify as pgd_bad().
@@ -212,12 +217,6 @@ static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
 	pgd_populate(mm, pgdp, p4dp);
 	WARN_ON(pgd_bad(READ_ONCE(*pgdp)));
 }
-#else
-static void pgd_clear_tests(pgd_t *pgdp) { }
-static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
-{
-}
-#endif
 
 static void pte_clear_tests(pte_t *ptep)
 {

> +
> +static void pte_clear_tests(pte_t *ptep)
> +{
> +	memset(ptep, RANDOM_NZVALUE, sizeof(pte_t));
> +	pte_clear(NULL, 0, ptep);
> +	WARN_ON(!pte_none(READ_ONCE(*ptep)));
> +}
> +
> +static void pmd_clear_tests(pmd_t *pmdp)
> +{
> +	memset(pmdp, RANDOM_NZVALUE, sizeof(pmd_t));
> +	pmd_clear(pmdp);
> +	WARN_ON(!pmd_none(READ_ONCE(*pmdp)));
> +}
> +
> +static void pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
> +			       pgtable_t pgtable)
> +{
> +	/*
> +	 * 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);
> +	WARN_ON(pmd_bad(READ_ONCE(*pmdp)));
> +}
> +
> +static bool pfn_range_valid(struct zone *z, unsigned long start_pfn,
> +			    unsigned long nr_pages)
> +{
> +	unsigned long i, end_pfn = start_pfn + nr_pages;
> +	struct page *page;
> +
> +	for (i = start_pfn; i < end_pfn; i++) {
> +		if (!pfn_valid(i))
> +			return false;
> +
> +		page = pfn_to_page(i);
> +
> +		if (page_zone(page) != z)
> +			return false;
> +
> +		if (PageReserved(page))
> +			return false;
> +
> +		if (page_count(page) > 0)
> +			return false;
> +
> +		if (PageHuge(page))
> +			return false;
> +	}
> +	return true;
> +}
> +
> +static struct page *alloc_gigantic_page(nodemask_t *nodemask,
> +					int nid, gfp_t gfp_mask, int order)
> +{
> +	struct zonelist *zonelist;
> +	struct zone *zone;
> +	struct zoneref *z;
> +	enum zone_type zonesel;
> +	unsigned long ret, pfn, flags, nr_pages;
> +
> +	nr_pages = 1UL << order;
> +	zonesel = gfp_zone(gfp_mask);
> +	zonelist = node_zonelist(nid, gfp_mask);
> +	for_each_zone_zonelist_nodemask(zone, z, zonelist, zonesel, nodemask) {
> +		spin_lock_irqsave(&zone->lock, flags);
> +		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
> +		while (zone_spans_pfn(zone, pfn + nr_pages - 1)) {
> +			if (pfn_range_valid(zone, pfn, nr_pages)) {
> +				spin_unlock_irqrestore(&zone->lock, flags);
> +				ret = alloc_contig_range(pfn, pfn + nr_pages,
> +							 MIGRATE_MOVABLE,
> +							 gfp_mask);
> +				if (!ret)
> +					return pfn_to_page(pfn);
> +				spin_lock_irqsave(&zone->lock, flags);
> +			}
> +			pfn += nr_pages;
> +		}
> +		spin_unlock_irqrestore(&zone->lock, flags);
> +	}
> +	return NULL;
> +}
> +
> +static struct page *alloc_mapped_page(void)
> +{
> +	gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
> +	struct page *page = NULL;
> +
> +	page = alloc_gigantic_page(&node_states[N_MEMORY], first_memory_node,
> +				   gfp_mask, get_order(PUD_SIZE));
> +	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 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 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;
> +	pte_t *ptep, *saved_ptep;
> +	pgprot_t prot = vm_get_page_prot(VMA_TEST_FLAGS);
> +	unsigned long vaddr = VADDR_TEST;
> +
> +	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.
> +	 */
> +	saved_p4dp = p4d_offset(pgdp, 0UL);
> +	saved_pudp = pud_offset(p4dp, 0UL);
> +	saved_pmdp = pmd_offset(pudp, 0UL);
> +	saved_ptep = pte_offset_map(pmdp, 0UL);
> +
> +	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(ptep);
> +	pmd_clear_tests(pmdp);
> +	pud_clear_tests(pudp);
> +	p4d_clear_tests(p4dp);
> +	pgd_clear_tests(pgdp);
> +
> +	pmd_populate_tests(mm, pmdp, (pgtable_t) page);

This is not correct for architectures that defines pgtable_t as pte_t
pointer, not struct page pointer.

> +	pud_populate_tests(mm, pudp, pmdp);
> +	p4d_populate_tests(mm, p4dp, pudp);
> +	pgd_populate_tests(mm, pgdp, p4dp);

This is wrong. All p?dp points to the second entry in page table entry.
This is not valid pointer for page table and triggers p?d_bad() on x86.

Use saved_p?dp instead.

> +
> +	p4d_free(mm, saved_p4dp);
> +	pud_free(mm, saved_pudp);
> +	pmd_free(mm, saved_pmdp);
> +	pte_free(mm, (pgtable_t) virt_to_page(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;
> +}
> +
> +static void __exit arch_pgtable_tests_exit(void) { }
> +
> +module_init(arch_pgtable_tests_init);
> +module_exit(arch_pgtable_tests_exit);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Anshuman Khandual <anshuman.khandual@xxxxxxx>");
> +MODULE_DESCRIPTION("Test archicture page table helpers");
> -- 
> 2.20.1
> 
> 

-- 
 Kirill A. Shutemov