[RFC,V2,1/1] mm/pgtable/debug: Add test validating architecture page table helpers

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 82b6a20898bd..d3dfbe984d41 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -115,3 +115,17 @@  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 338e528ad436..0e6ac3789ca8 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -84,6 +84,7 @@  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..41d6fa78a620
--- /dev/null
+++ b/mm/arch_pgtable_test.c
@@ -0,0 +1,400 @@ 
+// 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/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)
+#define VMA_TEST_FLAGS	(VM_READ|VM_WRITE|VM_EXEC)
+#define RANDOM_NZVALUE	(0xbe)
+
+static bool pud_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 = 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
+
+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;
+		return page;
+	}
+	return alloc_pages(gfp_mask, get_order(PMD_SIZE));
+}
+
+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;
+	}
+	free_pages((unsigned long)page_address(page), get_order(PMD_SIZE));
+}
+
+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);
+	pud_populate_tests(mm, pudp, pmdp);
+	p4d_populate_tests(mm, p4dp, pudp);
+	pgd_populate_tests(mm, pgdp, p4dp);
+
+	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@arm.com>");
+MODULE_DESCRIPTION("Test archicture page table helpers");