[PATCH v3 12/13] mm/debug_vm_pgtable/hugetlb: Disable hugetlb test on ppc64

[Anshuman Khandual]

On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
> The seems to be missing quite a lot of details w.r.t allocating
> the correct pgtable_t page (huge_pte_alloc()), holding the right
> lock (huge_pte_lock()) etc. The vma used is also not a hugetlb VMA.
> 
> ppc64 do have runtime checks within CONFIG_DEBUG_VM for most of these.
> Hence disable the test on ppc64.

Would really like this to get resolved in an uniform and better way
instead, i.e a modified hugetlb_advanced_tests() which works on all
platforms including ppc64.

In absence of a modified version, I do realize the situation here,
where DEBUG_VM_PGTABLE test either runs on ppc64 or just completely
remove hugetlb_advanced_tests() from other platforms as well.

> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>  mm/debug_vm_pgtable.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index a188b6e4e37e..21329c7d672f 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -813,6 +813,7 @@ static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot)
>  #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
>  }
>  
> +#ifndef CONFIG_PPC_BOOK3S_64
>  static void __init hugetlb_advanced_tests(struct mm_struct *mm,
>  					  struct vm_area_struct *vma,
>  					  pte_t *ptep, unsigned long pfn,
> @@ -855,6 +856,7 @@ static void __init hugetlb_advanced_tests(struct mm_struct *mm,
>  	pte = huge_ptep_get(ptep);
>  	WARN_ON(!(huge_pte_write(pte) && huge_pte_dirty(pte)));
>  }
> +#endif

In the worst case if we could not get a new hugetlb_advanced_tests() test
that works on all platforms, this might be the last fallback option. In
which case, it will require a proper comment section with a "FIXME: ",
explaining the current situation (and that #ifdef is temporary in nature)
and a hugetlb_advanced_tests() stub when CONFIG_PPC_BOOK3S_64 is enabled.

>  #else  /* !CONFIG_HUGETLB_PAGE */
>  static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot) { }
>  static void __init hugetlb_advanced_tests(struct mm_struct *mm,
> @@ -1065,7 +1067,9 @@ static int __init debug_vm_pgtable(void)
>  	pud_populate_tests(mm, pudp, saved_pmdp);
>  	spin_unlock(ptl);
>  
> +#ifndef CONFIG_PPC_BOOK3S_64
>  	hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
> +#endif

#ifdef will not be required here as there would be a stub definition
for hugetlb_advanced_tests() when CONFIG_PPC_BOOK3S_64 is enabled.

>  
>  	spin_lock(&mm->page_table_lock);
>  	p4d_clear_tests(mm, p4dp);
> 

But again, we should really try and avoid taking this path.