Message-ID: <8d754894-5c21-1287-82b6-7ac3b064af3d@redhat.com>
Date:   Mon, 19 Jul 2021 23:01:03 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, anshuman.khandual@....com,
        catalin.marinas@....com, will@...nel.org,
        akpm@...ux-foundation.org, chuhu@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v2 01/12] mm/debug_vm_pgtable: Introduce struct
 pgtable_debug_args

On 7/19/21 3:41 PM, 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 functions for various test
> cases need is the struct, to simplify the code. It also makes code
> 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.
> 
> This introduces "struct pgtable_debug_args". The struct is initialized
> and destroyed, but the information in the struct isn't used yet. They
> will be used in subsequent patches.
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   mm/debug_vm_pgtable.c | 196 +++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 195 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 1c922691aa61..0cc44e7c166e 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -58,6 +58,36 @@
>   #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;
> +
> +	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 +985,166 @@ 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) {
> +		page = pfn_to_page(args->pud_pfn);
> +		__free_pages(page, HPAGE_PUD_SHIFT - PAGE_SHIFT);
> +	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> +		   has_transparent_hugepage() &&
> +		   args->pmd_pfn != ULONG_MAX) {
> +		page = pfn_to_page(args->pmd_pfn);
> +		__free_pages(page, HPAGE_PMD_ORDER);
> +	} else if (args->pte_pfn != ULONG_MAX) {
> +		page = pfn_to_page(args->pte_pfn);
> +		__free_pages(page, 0);
> +	}
> +
> +	/* Free page table */
> +	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);
> +	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 */
> +	memset(args, 0, sizeof(*args));
> +	args->page_prot      = vm_get_page_prot(VMFLAGS);
> +	args->page_prot_none = __P000;
> +	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;
> +	}
> +
> +	/* Figure out the virtual address and allocate page table entries */
> +	args->vaddr = get_random_vaddr();
> +	args->pgdp = pgd_offset(args->mm, args->vaddr);
> +	args->p4dp = p4d_alloc(args->mm, args->pgdp, args->vaddr);
> +	args->pudp = args->p4dp ?
> +		     pud_alloc(args->mm, args->p4dp, args->vaddr) : NULL;
> +	args->pmdp = args->pudp ?
> +		     pmd_alloc(args->mm, args->pudp, args->vaddr) : NULL;
> +	args->ptep = args->pmdp ?
> +		     pte_alloc_map(args->mm, args->pmdp, args->vaddr) : NULL;
> +	if (!args->ptep) {
> +		pr_err("Failed to allocate page table\n");
> +		ret = -ENOMEM;
> +		goto error;
> +	}
> +
> +	/*
> +	 * The above page table entries will be modified. Lets save the
> +	 * page table entries so that they can be released when the tests
> +	 * are completed.
> +	 */
> +	args->start_p4dp = p4d_offset(args->pgdp, 0UL);
> +	args->start_pudp = pud_offset(args->p4dp, 0UL);
> +	args->start_pmdp = pmd_offset(args->pudp, 0UL);
> +	args->start_ptep = pmd_pgtable(READ_ONCE(*(args->pmdp)));
> +
> +	/*
> +	 * Figure out the fixed addresses, which are all around the kernel
> +	 * symbol (@start_kernel). The corresponding PFNs might be invalid,
> +	 * but it's fine as the following tests won't access the pages.
> +	 */
> +	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);
> +
> +	/*
> +	 * 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 = 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;
> +		}
> +	}
> +
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> +	    has_transparent_hugepage()) {
> +		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;
> +		}
> +	}
> +

As syzbot reported against v1 series, we could allocate pages larger than (1 << (MAX_ORDER - 1)) here.
So __GFP_NOWARN is needed here. I will fix it in v3 series.

> +	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 +1158,13 @@ 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 +1319,8 @@ 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

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