linux-kernel - Re: [PATCH v4 01/12] mm/debug_vm_pgtable: Introduce struct pgtable_debug

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Date:   Wed, 28 Jul 2021 17:38:01 +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 7/28/21 5:32 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);
> 
> 				     ^^^^ s/args->p4dp/args->start_p4dp ?
> 

Yes, It should be "args->start_p4dp" here. I will correct it in v5
after you finish review on v4.

Thanks,
Gavin