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Subject: Re: [PATCH v3 08/12] mm/debug_vm_pgtable: Use struct
 pgtable_debug_args in PMD modifying tests
To:     Gavin Shan <gshan@redhat.com>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, catalin.marinas@arm.com,
        will@kernel.org, akpm@linux-foundation.org, chuhu@redhat.com,
        shan.gavin@gmail.com
References: <20210719130613.334901-1-gshan@redhat.com>
 <20210719130613.334901-9-gshan@redhat.com>
 <52a61d4a-f93d-af9e-4a34-d8ea7c476838@arm.com>
 <e2707943-8645-a6d5-be15-7cf56791fedb@redhat.com>
 <876f9722-c307-560d-5efd-3613c312c7bd@arm.com>
 <8d8daf85-0015-4221-aad5-5baa03e3f699@redhat.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <68b6ab2a-4b6d-a0b8-f753-01fdc165b24a@arm.com>
Date:   Fri, 23 Jul 2021 08:03:48 +0530
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On 7/23/21 6:30 AM, Gavin Shan wrote:
> Hi Anshuman,
> 
> On 7/22/21 5:11 PM, Anshuman Khandual wrote:
>> On 7/22/21 12:11 PM, Gavin Shan wrote:
>>> On 7/22/21 3:45 PM, Anshuman Khandual wrote:
>>>> On 7/19/21 6:36 PM, Gavin Shan wrote:
>>>>> This uses struct pgtable_debug_args in PMD modifying tests. The allocated
>>>>> huge page is used when set_pmd_at() is used. The corresponding tests
>>>>> are skipped if the huge page doesn't exist. Besides, the unused variable
>>>>> @pmd_aligned in debug_vm_pgtable() is dropped.
>>>>
>>>> Please dont drop @pmd_aligned just yet.
>>>>
>>>
>>> We need do so. Otherwise, there is build warning to complain
>>> something like 'unused variable' after this patch is applied.
>>>
>>>>>
>>>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>>>>> ---
>>>>>    mm/debug_vm_pgtable.c | 102 ++++++++++++++++++++----------------------
>>>>>    1 file changed, 48 insertions(+), 54 deletions(-)
>>>>>
>>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>>>> index eb6dda88e0d9..cec3cbf99a6b 100644
>>>>> --- a/mm/debug_vm_pgtable.c
>>>>> +++ b/mm/debug_vm_pgtable.c
>>>>> @@ -213,54 +213,54 @@ static void __init pmd_basic_tests(struct pgtable_debug_args *args, int idx)
>>>>>        WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
>>>>>    }
>>>>>    -static void __init pmd_advanced_tests(struct mm_struct *mm,
>>>>> -                      struct vm_area_struct *vma, pmd_t *pmdp,
>>>>> -                      unsigned long pfn, unsigned long vaddr,
>>>>> -                      pgprot_t prot, pgtable_t pgtable)
>>>>> +static void __init pmd_advanced_tests(struct pgtable_debug_args *args)
>>>>>    {
>>>>>        pmd_t pmd;
>>>>> +    unsigned long vaddr = (args->vaddr & HPAGE_PMD_MASK);
>>>>>          if (!has_transparent_hugepage())
>>>>>            return;
>>>>>          pr_debug("Validating PMD advanced\n");
>>>>> -    /* Align the address wrt HPAGE_PMD_SIZE */
>>>>> -    vaddr &= HPAGE_PMD_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.
>>>>
>>>
>>> Ok.
>>>
>>>>> +    if (args->pmd_pfn == ULONG_MAX) {
>>>>> +        pr_debug("%s: Skipped\n", __func__);
>>>>> +        return;
>>>>> +    }
>>>>
>>>> Just return. Please dont call out "Skipped".
>>>>
>>>
>>> Ok.
>>>
>>>>>    -    pgtable_trans_huge_deposit(mm, pmdp, pgtable);
>>>>> +    pgtable_trans_huge_deposit(args->mm, args->pmdp, args->start_ptep);
>>>>>    -    pmd = pfn_pmd(pfn, prot);
>>>>> -    set_pmd_at(mm, vaddr, pmdp, pmd);
>>>>> -    pmdp_set_wrprotect(mm, vaddr, pmdp);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    pmd = pfn_pmd(args->pmd_pfn, args->page_prot);
>>>>> +    set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
>>>>> +    pmdp_set_wrprotect(args->mm, vaddr, args->pmdp);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(pmd_write(pmd));
>>>>> -    pmdp_huge_get_and_clear(mm, vaddr, pmdp);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    pmdp_huge_get_and_clear(args->mm, vaddr, args->pmdp);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(!pmd_none(pmd));
>>>>>    -    pmd = pfn_pmd(pfn, prot);
>>>>> +    pmd = pfn_pmd(args->pmd_pfn, args->page_prot);
>>>>>        pmd = pmd_wrprotect(pmd);
>>>>>        pmd = pmd_mkclean(pmd);
>>>>> -    set_pmd_at(mm, vaddr, pmdp, pmd);
>>>>> +    set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
>>>>>        pmd = pmd_mkwrite(pmd);
>>>>>        pmd = pmd_mkdirty(pmd);
>>>>> -    pmdp_set_access_flags(vma, vaddr, pmdp, pmd, 1);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    pmdp_set_access_flags(args->vma, vaddr, args->pmdp, pmd, 1);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(!(pmd_write(pmd) && pmd_dirty(pmd)));
>>>>> -    pmdp_huge_get_and_clear_full(vma, vaddr, pmdp, 1);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    pmdp_huge_get_and_clear_full(args->vma, vaddr, args->pmdp, 1);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(!pmd_none(pmd));
>>>>>    -    pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
>>>>> +    pmd = pmd_mkhuge(pfn_pmd(args->pmd_pfn, args->page_prot));
>>>>>        pmd = pmd_mkyoung(pmd);
>>>>> -    set_pmd_at(mm, vaddr, pmdp, pmd);
>>>>> -    pmdp_test_and_clear_young(vma, vaddr, pmdp);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    set_pmd_at(args->mm, vaddr, args->pmdp, pmd);
>>>>> +    pmdp_test_and_clear_young(args->vma, vaddr, args->pmdp);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(pmd_young(pmd));
>>>>>          /*  Clear the pte entries  */
>>>>> -    pmdp_huge_get_and_clear(mm, vaddr, pmdp);
>>>>> -    pgtable = pgtable_trans_huge_withdraw(mm, pmdp);
>>>>> +    pmdp_huge_get_and_clear(args->mm, vaddr, args->pmdp);
>>>>> +    pgtable_trans_huge_withdraw(args->mm, args->pmdp);
>>>>>    }
>>>>>      static void __init pmd_leaf_tests(struct pgtable_debug_args *args)
>>>>> @@ -417,12 +417,7 @@ static void __init pud_leaf_tests(struct pgtable_debug_args *args) { }
>>>>>    #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 mm_struct *mm,
>>>>> -                      struct vm_area_struct *vma, pmd_t *pmdp,
>>>>> -                      unsigned long pfn, unsigned long vaddr,
>>>>> -                      pgprot_t prot, pgtable_t pgtable)
>>>>> -{
>>>>> -}
>>>>> +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,
>>>>> @@ -435,11 +430,11 @@ static void __init pmd_savedwrite_tests(struct pgtable_debug_args *args) { }
>>>>>    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>>>      #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
>>>>> -static void __init pmd_huge_tests(pmd_t *pmdp, unsigned long pfn, pgprot_t prot)
>>>>> +static void __init pmd_huge_tests(struct pgtable_debug_args *args)
>>>>>    {
>>>>>        pmd_t pmd;
>>>>>    -    if (!arch_vmap_pmd_supported(prot))
>>>>> +    if (!arch_vmap_pmd_supported(args->page_prot))
>>>>>            return;
>>>>>          pr_debug("Validating PMD huge\n");
>>>>> @@ -447,10 +442,11 @@ static void __init pmd_huge_tests(pmd_t *pmdp, unsigned long pfn, pgprot_t prot)
>>>>>         * X86 defined pmd_set_huge() verifies that the given
>>>>>         * PMD is not a populated non-leaf entry.
>>>>>         */
>>>>> -    WRITE_ONCE(*pmdp, __pmd(0));
>>>>> -    WARN_ON(!pmd_set_huge(pmdp, __pfn_to_phys(pfn), prot));
>>>>> -    WARN_ON(!pmd_clear_huge(pmdp));
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    WRITE_ONCE(*(args->pmdp), __pmd(0));
>>>>
>>>> Possible extra braces.
>>>>
>>>
>>> Will drop it in v4, thanks!
>>>
>>>>> +    WARN_ON(!pmd_set_huge(args->pmdp, __pfn_to_phys(args->fixed_pmd_pfn),
>>>>> +                  args->page_prot));
>>>>
>>>> Dont break the line.
>>>>
>>>
>>> Ok.
>>>
>>>>> +    WARN_ON(!pmd_clear_huge(args->pmdp));
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(!pmd_none(pmd));
>>>>>    }
>>>>>    @@ -473,7 +469,7 @@ static void __init pud_huge_tests(pud_t *pudp, unsigned long pfn, pgprot_t prot)
>>>>>        WARN_ON(!pud_none(pud));
>>>>>    }
>>>>>    #else /* !CONFIG_HAVE_ARCH_HUGE_VMAP */
>>>>> -static void __init pmd_huge_tests(pmd_t *pmdp, unsigned long pfn, pgprot_t prot) { }
>>>>> +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) { }
>>>>>    #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
>>>>>    @@ -640,20 +636,19 @@ static void __init pte_clear_tests(struct pgtable_debug_args *args)
>>>>>        WARN_ON(!pte_none(pte));
>>>>>    }
>>>>>    -static void __init pmd_clear_tests(struct mm_struct *mm, pmd_t *pmdp)
>>>>> +static void __init pmd_clear_tests(struct pgtable_debug_args *args)
>>>>>    {
>>>>> -    pmd_t pmd = READ_ONCE(*pmdp);
>>>>> +    pmd_t pmd = READ_ONCE(*(args->pmdp));
>>>>>          pr_debug("Validating PMD clear\n");
>>>>>        pmd = __pmd(pmd_val(pmd) | RANDOM_ORVALUE);
>>>>> -    WRITE_ONCE(*pmdp, pmd);
>>>>> -    pmd_clear(pmdp);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    WRITE_ONCE(*(args->pmdp), pmd);
>>>>> +    pmd_clear(args->pmdp);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(!pmd_none(pmd));
>>>>>    }
>>>>>    -static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
>>>>> -                      pgtable_t pgtable)
>>>>> +static void __init pmd_populate_tests(struct pgtable_debug_args *args)
>>>>>    {
>>>>>        pmd_t pmd;
>>>>>    @@ -662,8 +657,8 @@ static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
>>>>>         * This entry points to next level page table page.
>>>>>         * Hence this must not qualify as pmd_bad().
>>>>>         */
>>>>> -    pmd_populate(mm, pmdp, pgtable);
>>>>> -    pmd = READ_ONCE(*pmdp);
>>>>> +    pmd_populate(args->mm, args->pmdp, args->start_ptep);
>>>>> +    pmd = READ_ONCE(*(args->pmdp));
>>>>>        WARN_ON(pmd_bad(pmd));
>>>>>    }
>>>>>    @@ -1159,7 +1154,7 @@ static int __init debug_vm_pgtable(void)
>>>>>        pgtable_t saved_ptep;
>>>>>        pgprot_t prot;
>>>>>        phys_addr_t paddr;
>>>>> -    unsigned long vaddr, pmd_aligned;
>>>>> +    unsigned long vaddr;
>>>>>        unsigned long pud_aligned;
>>>>>        spinlock_t *ptl = NULL;
>>>>>        int idx, ret;
>>>>> @@ -1194,7 +1189,6 @@ static int __init debug_vm_pgtable(void)
>>>>>         */
>>>>>        paddr = __pa_symbol(&start_kernel);
>>>>>    -    pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
>>>>
>>>> Please dont drop these just yet and wait until [PATCH 11/12].
>>>>
>>>
>>> Otherwise, it causes build warning: 'unused variable'.
>>
>> Why ? Just the evaluation of 'pmd_aligned' from 'paddr' should
>> be enough to avoid such warning. 'pmd_aligned' need not be used
>> afterwards.
>>
> 
> It's not enough to avoid the warning. I apply the patches till
> this one (PATCH[v3 08/12]) and have additional code to keep
> @pmd_aligned, then I run into build warning as below:
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index cec3cbf99a6b..961c9bb6fc7c 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -1154,7 +1154,7 @@ static int __init debug_vm_pgtable(void)
>         pgtable_t saved_ptep;
>         pgprot_t prot;
>         phys_addr_t paddr;
> -       unsigned long vaddr;
> +       unsigned long vaddr, pmd_aligned;
>         unsigned long pud_aligned;
>         spinlock_t *ptl = NULL;
>         int idx, ret;
> @@ -1189,6 +1189,7 @@ static int __init debug_vm_pgtable(void)
>          */
>         paddr = __pa_symbol(&start_kernel);
>  
> +       pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
>         pud_aligned = (paddr & PUD_MASK) >> PAGE_SHIFT;
>  
>         pgdp = pgd_offset(mm, vaddr);
> 
> [gwshan@gshan l]$ make W=1 mm/debug_vm_pgtable.o
>      :
> mm/debug_vm_pgtable.c: In function ‘debug_vm_pgtable’:
> mm/debug_vm_pgtable.c:1157:23: warning: variable ‘pmd_aligned’ set but not used [-Wunused-but-set-variable]
>  1157 |  unsigned long vaddr, pmd_aligned;
>       |                       ^~~~~~~~~~~
> 
> 
> By the way, 0-day is trying to build kernel with "W=1". It means the
> build warnings will be reported by 0-day if the unused variables aren't
> dropped from individual patches. It makes the review a bit harder. However,

It is not about keeping the review process simple. But rather the proposed
patch changing as much what is really required and nothing else.

> we still need to keep each individual patch complete to make 'git bisect'
> friendly.

With W=1 if this throws up a build error, I guess we dont have choice here.
We need to keep the build clean for each individual patch applies.