mm/debug_vm_pgtable: introduce struct pgtable_debug_args

Patch series "mm/debug_vm_pgtable: Enhancements", v6.

There are a couple of issues with current implementations and this series
tries to resolve the issues:

  (a) All needed information are scattered in variables, passed to various
      test functions. The code is organized in pretty much relaxed fashion.

  (b) The page isn't allocated from buddy during page table entry modifying
      tests. The page can be invalid, conflicting to the implementations
      of set_xxx_at() on ARM64. The target page is accessed so that the
      iCache can be flushed when execution permission is given on ARM64.
      Besides, the target page can be unmapped and accessing to it causes
      kernel crash.

"struct pgtable_debug_args" is introduced to address issue (a).  For issue
(b), the used page is allocated from buddy in page table entry modifying
tests.  The corresponding tets will be skipped if we fail to allocate the
(huge) page.  For other test cases, the original page around to kernel
symbol (@start_kernel) is still used.

The patches are organized as below.  PATCH[2-10] could be combined to one
patch, but it will make the review harder:

  PATCH[1] introduces "struct pgtable_debug_args" as place holder of all
           needed information. With it, the old and new implementation
           can coexist.
  PATCH[2-10] uses "struct pgtable_debug_args" in various test functions.
  PATCH[11] removes the unused code for old implementation.
  PATCH[12] fixes the issue of corrupted page flag for ARM64

This patch (of 6):

In debug_vm_pgtable(), there are many local variables introduced to track
the needed information and they are passed to the functions for various
test cases.  It'd better to introduce a struct as place holder for these
information.  With it, what the tests functions need is the struct.  In
this way, the code is simplified and easier to be maintained.

Besides, set_xxx_at() could access the data on the corresponding pages in
the page table modifying tests.  So the accessed pages in the tests should
have been allocated from buddy.  Otherwise, we're accessing pages that
aren't owned by us.  This causes issues like page flag corruption or
kernel crash on accessing unmapped page when CONFIG_DEBUG_PAGEALLOC is
enabled.

This introduces "struct pgtable_debug_args".  The struct is initialized
and destroyed, but the information in the struct isn't used yet.  It will
be used in subsequent patches.

Link: https://lkml.kernel.org/r/20210809092631.1888748-1-gshan@redhat.com
Link: https://lkml.kernel.org/r/20210809092631.1888748-2-gshan@redhat.comSigned-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>	[powerpc 8xx]
Tested-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>	[s390]
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Chunyu Hu <chuhu@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/debug_vm_pgtable.c

@@ -58,6 +58,37 @@
 #define RANDOM_ORVALUE (GENMASK(BITS_PER_LONG - 1, 0) & ~ARCH_SKIP_MASK)
 #define RANDOM_NZVALUE	GENMASK(7, 0)
 
+struct pgtable_debug_args {
+	struct mm_struct	*mm;
+	struct vm_area_struct	*vma;
+
+	pgd_t			*pgdp;
+	p4d_t			*p4dp;
+	pud_t			*pudp;
+	pmd_t			*pmdp;
+	pte_t			*ptep;
+
+	p4d_t			*start_p4dp;
+	pud_t			*start_pudp;
+	pmd_t			*start_pmdp;
+	pgtable_t		start_ptep;
+
+	unsigned long		vaddr;
+	pgprot_t		page_prot;
+	pgprot_t		page_prot_none;
+
+	bool			is_contiguous_page;
+	unsigned long		pud_pfn;
+	unsigned long		pmd_pfn;
+	unsigned long		pte_pfn;
+
+	unsigned long		fixed_pgd_pfn;
+	unsigned long		fixed_p4d_pfn;
+	unsigned long		fixed_pud_pfn;
+	unsigned long		fixed_pmd_pfn;
+	unsigned long		fixed_pte_pfn;
+};
+
 static void __init pte_basic_tests(unsigned long pfn, int idx)
 {
 	pgprot_t prot = protection_map[idx];
@@ -955,8 +986,239 @@ static unsigned long __init get_random_vaddr(void)
 	return random_vaddr;
 }
 
+static void __init destroy_args(struct pgtable_debug_args *args)
+{
+	struct page *page = NULL;
+
+	/* Free (huge) page */
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
+	    has_transparent_hugepage() &&
+	    args->pud_pfn != ULONG_MAX) {
+		if (args->is_contiguous_page) {
+			free_contig_range(args->pud_pfn,
+					  (1 << (HPAGE_PUD_SHIFT - PAGE_SHIFT)));
+		} else {
+			page = pfn_to_page(args->pud_pfn);
+			__free_pages(page, HPAGE_PUD_SHIFT - PAGE_SHIFT);
+		}
+
+		args->pud_pfn = ULONG_MAX;
+		args->pmd_pfn = ULONG_MAX;
+		args->pte_pfn = ULONG_MAX;
+	}
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    has_transparent_hugepage() &&
+	    args->pmd_pfn != ULONG_MAX) {
+		if (args->is_contiguous_page) {
+			free_contig_range(args->pmd_pfn, (1 << HPAGE_PMD_ORDER));
+		} else {
+			page = pfn_to_page(args->pmd_pfn);
+			__free_pages(page, HPAGE_PMD_ORDER);
+		}
+
+		args->pmd_pfn = ULONG_MAX;
+		args->pte_pfn = ULONG_MAX;
+	}
+
+	if (args->pte_pfn != ULONG_MAX) {
+		page = pfn_to_page(args->pte_pfn);
+		__free_pages(page, 0);
+
+		args->pte_pfn = ULONG_MAX;
+	}
+
+	/* Free page table entries */
+	if (args->start_ptep) {
+		pte_free(args->mm, args->start_ptep);
+		mm_dec_nr_ptes(args->mm);
+	}
+
+	if (args->start_pmdp) {
+		pmd_free(args->mm, args->start_pmdp);
+		mm_dec_nr_pmds(args->mm);
+	}
+
+	if (args->start_pudp) {
+		pud_free(args->mm, args->start_pudp);
+		mm_dec_nr_puds(args->mm);
+	}
+
+	if (args->start_p4dp)
+		p4d_free(args->mm, args->start_p4dp);
+
+	/* Free vma and mm struct */
+	if (args->vma)
+		vm_area_free(args->vma);
+
+	if (args->mm)
+		mmdrop(args->mm);
+}
+
+static struct page * __init
+debug_vm_pgtable_alloc_huge_page(struct pgtable_debug_args *args, int order)
+{
+	struct page *page = NULL;
+
+#ifdef CONFIG_CONTIG_ALLOC
+	if (order >= MAX_ORDER) {
+		page = alloc_contig_pages((1 << order), GFP_KERNEL,
+					  first_online_node, NULL);
+		if (page) {
+			args->is_contiguous_page = true;
+			return page;
+		}
+	}
+#endif
+
+	if (order < MAX_ORDER)
+		page = alloc_pages(GFP_KERNEL, order);
+
+	return page;
+}
+
+static int __init init_args(struct pgtable_debug_args *args)
+{
+	struct page *page = NULL;
+	phys_addr_t phys;
+	int ret = 0;
+
+	/*
+	 * Initialize the debugging data.
+	 *
+	 * __P000 (or even __S000) will help create page table entries with
+	 * PROT_NONE permission as required for pxx_protnone_tests().
+	 */
+	memset(args, 0, sizeof(*args));
+	args->vaddr              = get_random_vaddr();
+	args->page_prot          = vm_get_page_prot(VMFLAGS);
+	args->page_prot_none     = __P000;
+	args->is_contiguous_page = false;
+	args->pud_pfn            = ULONG_MAX;
+	args->pmd_pfn            = ULONG_MAX;
+	args->pte_pfn            = ULONG_MAX;
+	args->fixed_pgd_pfn      = ULONG_MAX;
+	args->fixed_p4d_pfn      = ULONG_MAX;
+	args->fixed_pud_pfn      = ULONG_MAX;
+	args->fixed_pmd_pfn      = ULONG_MAX;
+	args->fixed_pte_pfn      = ULONG_MAX;
+
+	/* Allocate mm and vma */
+	args->mm = mm_alloc();
+	if (!args->mm) {
+		pr_err("Failed to allocate mm struct\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	args->vma = vm_area_alloc(args->mm);
+	if (!args->vma) {
+		pr_err("Failed to allocate vma\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	/*
+	 * Allocate page table entries. They will be modified in the tests.
+	 * Lets save the page table entries so that they can be released
+	 * when the tests are completed.
+	 */
+	args->pgdp = pgd_offset(args->mm, args->vaddr);
+	args->p4dp = p4d_alloc(args->mm, args->pgdp, args->vaddr);
+	if (!args->p4dp) {
+		pr_err("Failed to allocate p4d entries\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+	args->start_p4dp = p4d_offset(args->pgdp, 0UL);
+	WARN_ON(!args->start_p4dp);
+
+	args->pudp = pud_alloc(args->mm, args->p4dp, args->vaddr);
+	if (!args->pudp) {
+		pr_err("Failed to allocate pud entries\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+	args->start_pudp = pud_offset(args->p4dp, 0UL);
+	WARN_ON(!args->start_pudp);
+
+	args->pmdp = pmd_alloc(args->mm, args->pudp, args->vaddr);
+	if (!args->pmdp) {
+		pr_err("Failed to allocate pmd entries\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+	args->start_pmdp = pmd_offset(args->pudp, 0UL);
+	WARN_ON(!args->start_pmdp);
+
+	if (pte_alloc(args->mm, args->pmdp)) {
+		pr_err("Failed to allocate pte entries\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+	args->start_ptep = pmd_pgtable(READ_ONCE(*args->pmdp));
+	WARN_ON(!args->start_ptep);
+
+	/*
+	 * PFN for mapping at PTE level is determined from a standard kernel
+	 * text symbol. But pfns for higher page table levels are derived by
+	 * masking lower bits of this real pfn. These derived pfns might not
+	 * exist on the platform but that does not really matter as pfn_pxx()
+	 * helpers will still create appropriate entries for the test. This
+	 * helps avoid large memory block allocations to be used for mapping
+	 * at higher page table levels in some of the tests.
+	 */
+	phys = __pa_symbol(&start_kernel);
+	args->fixed_pgd_pfn = __phys_to_pfn(phys & PGDIR_MASK);
+	args->fixed_p4d_pfn = __phys_to_pfn(phys & P4D_MASK);
+	args->fixed_pud_pfn = __phys_to_pfn(phys & PUD_MASK);
+	args->fixed_pmd_pfn = __phys_to_pfn(phys & PMD_MASK);
+	args->fixed_pte_pfn = __phys_to_pfn(phys & PAGE_MASK);
+	WARN_ON(!pfn_valid(args->fixed_pte_pfn));
+
+	/*
+	 * Allocate (huge) pages because some of the tests need to access
+	 * the data in the pages. The corresponding tests will be skipped
+	 * if we fail to allocate (huge) pages.
+	 */
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
+	    has_transparent_hugepage()) {
+		page = debug_vm_pgtable_alloc_huge_page(args,
+				HPAGE_PUD_SHIFT - PAGE_SHIFT);
+		if (page) {
+			args->pud_pfn = page_to_pfn(page);
+			args->pmd_pfn = args->pud_pfn;
+			args->pte_pfn = args->pud_pfn;
+			return 0;
+		}
+	}
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+	    has_transparent_hugepage()) {
+		page = debug_vm_pgtable_alloc_huge_page(args, HPAGE_PMD_ORDER);
+		if (page) {
+			args->pmd_pfn = page_to_pfn(page);
+			args->pte_pfn = args->pmd_pfn;
+			return 0;
+		}
+	}
+
+	page = alloc_pages(GFP_KERNEL, 0);
+	if (page)
+		args->pte_pfn = page_to_pfn(page);
+
+	return 0;
+
+error:
+	destroy_args(args);
+	return ret;
+}
+
 static int __init debug_vm_pgtable(void)
 {
+	struct pgtable_debug_args args;
 	struct vm_area_struct *vma;
 	struct mm_struct *mm;
 	pgd_t *pgdp;
@@ -970,9 +1232,13 @@ static int __init debug_vm_pgtable(void)
 	unsigned long vaddr, pte_aligned, pmd_aligned;
 	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
 	spinlock_t *ptl = NULL;
-	int idx;
+	int idx, ret;
 
 	pr_info("Validating architecture page table helpers\n");
+	ret = init_args(&args);
+	if (ret)
+		return ret;
+
 	prot = vm_get_page_prot(VMFLAGS);
 	vaddr = get_random_vaddr();
 	mm = mm_alloc();
@@ -1127,6 +1393,8 @@ static int __init debug_vm_pgtable(void)
 	mm_dec_nr_pmds(mm);
 	mm_dec_nr_ptes(mm);
 	mmdrop(mm);
+
+	destroy_args(&args);
 	return 0;
 }
 late_initcall(debug_vm_pgtable);