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Date: Thu, 29 Jul 2021 19:40:30 +1000
From: Gavin Shan <gshan@...hat.com>
To: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, gerald.schaefer@...ux.ibm.com,
aneesh.kumar@...ux.ibm.com, christophe.leroy@...roup.eu,
cai@....pw, catalin.marinas@....com, will@...nel.org,
akpm@...ux-foundation.org, chuhu@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v4 01/12] mm/debug_vm_pgtable: Introduce struct
pgtable_debug_args
Hi Anshuman,
On 7/29/21 2:45 PM, Anshuman Khandual wrote:
> On 7/27/21 11:43 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@...hat.com>
>> ---
>> mm/debug_vm_pgtable.c | 280 +++++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 279 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 1c922691aa61..8c7361643166 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 +986,249 @@ 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);
>> + }
>> +
>> + /* 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->p4dp);
>> +
>> + /* Free vma and mm struct */
>> + if (args->vma)
>> + vm_area_free(args->vma);
>
> Small nit, needs an extra line here.
>
Yes.
>> + if (args->mm)
>> + mmdrop(args->mm);
>> +}
>> +
>> +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);
>
> Please move these two lines up to the previous block as args->start_p4dp
> is primarily derived from args->pgdp. Also please do the same for all
> others blocks down here.
>
Good point. I will do in v5.
>> + 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);
>> + args->ptep = pte_alloc_map(args->mm, args->pmdp, args->vaddr);
>> + if (!args->ptep) {
>> + 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.
>> + */
>> +#ifdef CONFIG_CONTIG_ALLOC
>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>> + IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
>> + has_transparent_hugepage() &&
>> + (HPAGE_PUD_SHIFT - PAGE_SHIFT) >= MAX_ORDER) {
>> + page = alloc_contig_pages((1 << (HPAGE_PUD_SHIFT - PAGE_SHIFT)),
>> + GFP_KERNEL, first_online_node, NULL);
>> + if (page) {
>> + args->is_contiguous_page = true;
>> + args->pud_pfn = page_to_pfn(page);
>> + args->pmd_pfn = args->pud_pfn;
>> + args->pte_pfn = args->pud_pfn;
>> + return 0;
>> + }
>> + }
>> +#endif
>> +
>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>> + IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) &&
>> + has_transparent_hugepage() &&
>> + (HPAGE_PUD_SHIFT - PAGE_SHIFT) < MAX_ORDER) {
>> + page = alloc_pages(GFP_KERNEL, 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;
>> + }
>> + }
>> +
>> +#ifdef CONFIG_CONTIG_ALLOC
>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>> + has_transparent_hugepage() &&
>> + HPAGE_PMD_ORDER >= MAX_ORDER) {
>> + page = alloc_contig_pages((1 << HPAGE_PMD_ORDER), GFP_KERNEL,
>> + first_online_node, NULL);
>> + if (page) {
>> + args->is_contiguous_page = true;
>> + args->pmd_pfn = page_to_pfn(page);
>> + args->pte_pfn = args->pmd_pfn;
>> + return 0;
>> + }
>> + }
>> +#endif
>> +
>> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>> + has_transparent_hugepage() &&
>> + HPAGE_PMD_ORDER < MAX_ORDER) {
>> + page = alloc_pages(GFP_KERNEL, HPAGE_PMD_ORDER);
>> + if (page) {
>> + args->pmd_pfn = page_to_pfn(page);
>> + args->pte_pfn = args->pmd_pfn;
>> + return 0;
>> + }
>> + }
>
> This can be simplified further. Could you please define a helper alloc_huge_page()
> which compares the order against MAX_ORDER and calls either alloc_contig_pages()
> when CONFIG_CONTIG_ALLOC or alloc_pages(). This will result in reduced code and
> CONFIG_CONTIG_ALLOC will move into the helper as well.
>
Yes, I will introduce a helper for this, but the function name will be
debug_vm_pgtable_alloc_huge_page() because alloc_huge_page() has been
declared in include/linux/hugetlb.h
>> +
>> + 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 +1242,13 @@ 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 +1403,8 @@ 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);
>>
>
> Otherwise LGTM.
>
I will treat this as r-b in v5.
Thanks,
Gavin
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