Re: [PATCH v5 01/12] mm/debug_vm_pgtable: Introduce struct pgtable_debug_args
From: Gavin Shan
Date: Tue Aug 03 2021 - 01:22:09 EST
Hi Anshuman,
On 8/3/21 2:42 PM, Anshuman Khandual wrote:
On 8/2/21 11:34 AM, Gavin Shan wrote:
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.
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
mm/debug_vm_pgtable.c | 269 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 268 insertions(+), 1 deletion(-)
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 1c922691aa61..6a825f0e7cd7 100644
--- a/mm/debug_vm_pgtable.c
+++ b/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 +986,238 @@ 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 ?
I was thinking of this. It doesn't matter to set @pte_pfn to
ULONG_MAX as it's not used afterwards. However, I will add this
in v6 for consistency.
+ }
+
+ /* 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)
Small nit, formatting like below would have been better. But dont change yet
unless there is a respin.
Yes, will fix in v6.
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);
+ args->start_p4dp = p4d_offset(args->pgdp, 0UL);
+ WARN_ON(!args->start_p4dp);
+ if (!args->p4dp) {
+ pr_err("Failed to allocate p4d entries\n");
+ ret = -ENOMEM;
+ goto error;
+ }
Expected like this instead. 'args->start_p4dp' should not be evaluated
unless 'args->p4dp' allocation succeeds. Otherwise on the error path,
it would call p4d_free(args->mm, args->start_p4dp) freeing up a page
table page which was never allocated !
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);
I had requested just to move these two sentences into the previous code
block, without changing any order. This is also applicable for all other
page table levels below.
Yeah, I misunderstood your comments on v5 series. I wrongly thought
NULL is returned from p4d_offset() if p4d_alloc() fails, without
checking the implementation of p4d_offset() closely. I will fix
it in v6. However, I will hold posting v6 to see if there are
more comments on v5.
+
+ args->pudp = pud_alloc(args->mm, args->p4dp, args->vaddr);
+ args->start_pudp = pud_offset(args->p4dp, 0UL);
+ WARN_ON(!args->start_pudp);
+ if (!args->pudp) {
+ pr_err("Failed to allocate pud entries\n");
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ args->pmdp = pmd_alloc(args->mm, args->pudp, args->vaddr);
+ args->start_pmdp = pmd_offset(args->pudp, 0UL);
+ WARN_ON(!args->start_pmdp);
+ if (!args->pmdp) {
+ pr_err("Failed to allocate pmd entries\n");
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ args->ptep = pte_alloc_map(args->mm, args->pmdp, args->vaddr);
+ args->start_ptep = pmd_pgtable(READ_ONCE(*args->pmdp));
+ WARN_ON(!args->start_ptep);
+ if (!args->ptep) {
+ pr_err("Failed to allocate pte entries\n");
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ /*
+ * 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 +1231,13 @@ 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 +1392,8 @@ 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);
Thanks,
Gavin