Date:   Thu, 22 Jul 2021 11:09:25 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org, chuhu@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v3 09/12] mm/debug_vm_pgtable: Use struct
 pgtable_debug_args in PUD modifying tests


On 7/19/21 6:36 PM, Gavin Shan wrote:
> This uses struct pgtable_debug_args in PUD modifying tests. The allocated
> huge page is used when set_pud_at() is used. The corresponding tests
> are skipped if the huge page doesn't exist. Besides, the following unused
> variables in debug_vm_pgtable() are dropped: @prot, @paddr, @pud_aligned.

Please dont drop @prot, @paddr, @pud_aligned just yet.

> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>  mm/debug_vm_pgtable.c | 130 ++++++++++++++++--------------------------
>  1 file changed, 50 insertions(+), 80 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index cec3cbf99a6b..57b7ead0708b 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -338,55 +338,55 @@ static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx)
>  	WARN_ON(!pud_bad(pud_mkhuge(pud)));
>  }
>  
> -static void __init pud_advanced_tests(struct mm_struct *mm,
> -				      struct vm_area_struct *vma, pud_t *pudp,
> -				      unsigned long pfn, unsigned long vaddr,
> -				      pgprot_t prot)
> +static void __init pud_advanced_tests(struct pgtable_debug_args *args)
>  {
> +	unsigned long vaddr = (args->vaddr & HPAGE_PUD_MASK);
>  	pud_t pud;
>  
>  	if (!has_transparent_hugepage())
>  		return;
>  
>  	pr_debug("Validating PUD advanced\n");
> -	/* Align the address wrt HPAGE_PUD_SIZE */
> -	vaddr &= HPAGE_PUD_MASK;

Please just leave these unchanged. If has_transparent_hugepage() evaluates
negative, it skips the masking operation. As mentioned earlier please avoid
changing the test in any manner during these transition patches.

> +	if (args->pud_pfn == ULONG_MAX) {
> +		pr_debug("%s: Skipped\n", __func__);

Just return. Please dont call out "Skipped". Applicable for all transition
patches here.

> +		return;
> +	}
>  
> -	pud = pfn_pud(pfn, prot);
> -	set_pud_at(mm, vaddr, pudp, pud);
> -	pudp_set_wrprotect(mm, vaddr, pudp);
> -	pud = READ_ONCE(*pudp);
> +	pud = pfn_pud(args->pud_pfn, args->page_prot);
> +	set_pud_at(args->mm, vaddr, args->pudp, pud);
> +	pudp_set_wrprotect(args->mm, vaddr, args->pudp);
> +	pud = READ_ONCE(*(args->pudp));

Seems like an extra braces while de-referencing arg->pudp. Could these be
dropped. Just READ_ONCE(*args->pudp).

>  	WARN_ON(pud_write(pud));
>  
>  #ifndef __PAGETABLE_PMD_FOLDED
> -	pudp_huge_get_and_clear(mm, vaddr, pudp);
> -	pud = READ_ONCE(*pudp);
> +	pudp_huge_get_and_clear(args->mm, vaddr, args->pudp);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(!pud_none(pud));
>  #endif /* __PAGETABLE_PMD_FOLDED */
> -	pud = pfn_pud(pfn, prot);
> +	pud = pfn_pud(args->pud_pfn, args->page_prot);
>  	pud = pud_wrprotect(pud);
>  	pud = pud_mkclean(pud);
> -	set_pud_at(mm, vaddr, pudp, pud);
> +	set_pud_at(args->mm, vaddr, args->pudp, pud);
>  	pud = pud_mkwrite(pud);
>  	pud = pud_mkdirty(pud);
> -	pudp_set_access_flags(vma, vaddr, pudp, pud, 1);
> -	pud = READ_ONCE(*pudp);
> +	pudp_set_access_flags(args->vma, vaddr, args->pudp, pud, 1);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(!(pud_write(pud) && pud_dirty(pud)));
>  
>  #ifndef __PAGETABLE_PMD_FOLDED
> -	pudp_huge_get_and_clear_full(mm, vaddr, pudp, 1);
> -	pud = READ_ONCE(*pudp);
> +	pudp_huge_get_and_clear_full(args->mm, vaddr, args->pudp, 1);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(!pud_none(pud));
>  #endif /* __PAGETABLE_PMD_FOLDED */
>  
> -	pud = pfn_pud(pfn, prot);
> +	pud = pfn_pud(args->pud_pfn, args->page_prot);
>  	pud = pud_mkyoung(pud);
> -	set_pud_at(mm, vaddr, pudp, pud);
> -	pudp_test_and_clear_young(vma, vaddr, pudp);
> -	pud = READ_ONCE(*pudp);
> +	set_pud_at(args->mm, vaddr, args->pudp, pud);
> +	pudp_test_and_clear_young(args->vma, vaddr, args->pudp);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(pud_young(pud));
>  
> -	pudp_huge_get_and_clear(mm, vaddr, pudp);
> +	pudp_huge_get_and_clear(args->mm, vaddr, args->pudp);
>  }
>  
>  static void __init pud_leaf_tests(struct pgtable_debug_args *args)
> @@ -406,24 +406,14 @@ static void __init pud_leaf_tests(struct pgtable_debug_args *args)
>  }
>  #else  /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>  static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx) { }
> -static void __init pud_advanced_tests(struct mm_struct *mm,
> -				      struct vm_area_struct *vma, pud_t *pudp,
> -				      unsigned long pfn, unsigned long vaddr,
> -				      pgprot_t prot)
> -{
> -}
> +static void __init pud_advanced_tests(struct pgtable_debug_args *args) { }
>  static void __init pud_leaf_tests(struct pgtable_debug_args *args) { }
>  #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>  #else  /* !CONFIG_TRANSPARENT_HUGEPAGE */
>  static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx) { }
>  static void __init pud_basic_tests(struct pgtable_debug_args *args, int idx) { }
>  static void __init pmd_advanced_tests(struct pgtable_debug_args *args) { }
> -static void __init pud_advanced_tests(struct mm_struct *mm,
> -				      struct vm_area_struct *vma, pud_t *pudp,
> -				      unsigned long pfn, unsigned long vaddr,
> -				      pgprot_t prot)
> -{
> -}
> +static void __init pud_advanced_tests(struct pgtable_debug_args *args) { }
>  static void __init pmd_leaf_tests(struct pgtable_debug_args *args) { }
>  static void __init pud_leaf_tests(struct pgtable_debug_args *args) { }
>  static void __init pmd_savedwrite_tests(struct pgtable_debug_args *args) { }
> @@ -450,11 +440,11 @@ static void __init pmd_huge_tests(struct pgtable_debug_args *args)
>  	WARN_ON(!pmd_none(pmd));
>  }
>  
> -static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot)
> +static void __init pud_huge_tests(struct pgtable_debug_args *args)
>  {
>  	pud_t pud;
>  
> -	if (!arch_vmap_pud_supported(prot))
> +	if (!arch_vmap_pud_supported(args->page_prot))
>  		return;
>  
>  	pr_debug("Validating PUD huge\n");
> @@ -462,15 +452,16 @@ static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot)
>  	 * X86 defined pud_set_huge() verifies that the given
>  	 * PUD is not a populated non-leaf entry.
>  	 */
> -	WRITE_ONCE(*pudp, __pud(0));
> -	WARN_ON(!pud_set_huge(pudp, __pfn_to_phys(pfn), prot));
> -	WARN_ON(!pud_clear_huge(pudp));
> -	pud = READ_ONCE(*pudp);
> +	WRITE_ONCE(*(args->pudp), __pud(0));
> +	WARN_ON(!pud_set_huge(args->pudp, __pfn_to_phys(args->fixed_pud_pfn),
> +			      args->page_prot));

Please dont break the line, we could go upto 100 width. Please do
the same for the entire series. Improves the readability.

> +	WARN_ON(!pud_clear_huge(args->pudp));
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(!pud_none(pud));
>  }
>  #else /* !CONFIG_HAVE_ARCH_HUGE_VMAP */
>  static void __init pmd_huge_tests(struct pgtable_debug_args *args) { }
> -static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot) { }
> +static void __init pud_huge_tests(struct pgtable_debug_args *args) { }
>  #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
>  
>  static void __init p4d_basic_tests(void)
> @@ -492,27 +483,26 @@ static void __init pgd_basic_tests(void)
>  }
>  
>  #ifndef __PAGETABLE_PUD_FOLDED
> -static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp)
> +static void __init pud_clear_tests(struct pgtable_debug_args *args)
>  {
> -	pud_t pud = READ_ONCE(*pudp);
> +	pud_t pud = READ_ONCE(*(args->pudp));
>  
> -	if (mm_pmd_folded(mm))
> +	if (mm_pmd_folded(args->mm))
>  		return;
>  
>  	pr_debug("Validating PUD clear\n");
>  	pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
> -	WRITE_ONCE(*pudp, pud);
> -	pud_clear(pudp);
> -	pud = READ_ONCE(*pudp);
> +	WRITE_ONCE(*(args->pudp), pud);
> +	pud_clear(args->pudp);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(!pud_none(pud));
>  }
>  
> -static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> -				      pmd_t *pmdp)
> +static void __init pud_populate_tests(struct pgtable_debug_args *args)
>  {
>  	pud_t pud;
>  
> -	if (mm_pmd_folded(mm))
> +	if (mm_pmd_folded(args->mm))
>  		return;
>  
>  	pr_debug("Validating PUD populate\n");
> @@ -520,16 +510,13 @@ static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
>  	 * This entry points to next level page table page.
>  	 * Hence this must not qualify as pud_bad().
>  	 */
> -	pud_populate(mm, pudp, pmdp);
> -	pud = READ_ONCE(*pudp);
> +	pud_populate(args->mm, args->pudp, args->start_pmdp);
> +	pud = READ_ONCE(*(args->pudp));
>  	WARN_ON(pud_bad(pud));
>  }
>  #else  /* !__PAGETABLE_PUD_FOLDED */
> -static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp) { }
> -static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> -				      pmd_t *pmdp)
> -{
> -}
> +static void __init pud_clear_tests(struct pgtable_debug_args *args) { }
> +static void __init pud_populate_tests(struct pgtable_debug_args *args) { }
>  #endif /* PAGETABLE_PUD_FOLDED */
>  
>  #ifndef __PAGETABLE_P4D_FOLDED
> @@ -1152,10 +1139,7 @@ static int __init debug_vm_pgtable(void)
>  	pud_t *pudp, *saved_pudp;
>  	pmd_t *pmdp, *saved_pmdp, pmd;
>  	pgtable_t saved_ptep;
> -	pgprot_t prot;
> -	phys_addr_t paddr;
>  	unsigned long vaddr;
> -	unsigned long pud_aligned;
>  	spinlock_t *ptl = NULL;
>  	int idx, ret;
>  
> @@ -1164,7 +1148,6 @@ static int __init debug_vm_pgtable(void)
>  	if (ret)
>  		return ret;
>  
> -	prot = vm_get_page_prot(VMFLAGS);

Please dont drop these just yet and wait until [PATCH 11/12].

>  	vaddr = get_random_vaddr();
>  	mm = mm_alloc();
>  	if (!mm) {
> @@ -1178,19 +1161,6 @@ static int __init debug_vm_pgtable(void)
>  		return 1;
>  	}
>  
> -	/*
> -	 * 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.
> -	 */

Please move this comment as is to the right place inside init_args()
in the first patch itself. If possible all comments should be moved
during the first patch and just the code remains till [PATCH 11/12].

> -	paddr = __pa_symbol(&start_kernel);
> -
> -	pud_aligned = (paddr & PUD_MASK) >> PAGE_SHIFT;
> -

Please dont drop these just yet and wait until [PATCH 11/12].

>  	pgdp = pgd_offset(mm, vaddr);
>  	p4dp = p4d_alloc(mm, pgdp, vaddr);
>  	pudp = pud_alloc(mm, p4dp, vaddr);
> @@ -1282,11 +1252,11 @@ static int __init debug_vm_pgtable(void)
>  	pmd_populate_tests(&args);
>  	spin_unlock(ptl);
>  
> -	ptl = pud_lock(mm, pudp);
> -	pud_clear_tests(mm, pudp);
> -	pud_advanced_tests(mm, vma, pudp, pud_aligned, vaddr, prot);
> -	pud_huge_tests(pudp, pud_aligned, prot);
> -	pud_populate_tests(mm, pudp, saved_pmdp);
> +	ptl = pud_lock(args.mm, args.pudp);
> +	pud_clear_tests(&args);
> +	pud_advanced_tests(&args);
> +	pud_huge_tests(&args);
> +	pud_populate_tests(&args);
>  	spin_unlock(ptl);
>  
>  	spin_lock(&mm->page_table_lock);
> 

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