Re: [PATCH v2 1/3] userfaultfd: use vma_pagesize for all huge page size calculation

[Wei Yang <richardw.yang@linux.intel.com>]

On Mon, Oct 07, 2019 at 03:55:21PM -0700, Mike Kravetz wrote:
>On 9/28/19 5:45 PM, Wei Yang wrote:
>> On Fri, Sep 27, 2019 at 03:10:33PM -0700, Andrew Morton wrote:
>>> On Fri, 27 Sep 2019 15:00:30 +0800 Wei Yang <richardw.yang@linux.intel.com> wrote:
>>>
>>>> In function __mcopy_atomic_hugetlb, we use two variables to deal with
>>>> huge page size: vma_hpagesize and huge_page_size.
>>>>
>>>> Since they are the same, it is not necessary to use two different
>>>> mechanism. This patch makes it consistent by all using vma_hpagesize.
>>>>
>>>> --- a/mm/userfaultfd.c
>>>> +++ b/mm/userfaultfd.c
>>>> @@ -262,7 +262,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
>>>>  		pte_t dst_pteval;
>>>>  
>>>>  		BUG_ON(dst_addr >= dst_start + len);
>>>> -		VM_BUG_ON(dst_addr & ~huge_page_mask(h));
>>>> +		VM_BUG_ON(dst_addr & (vma_hpagesize - 1));
>>>>  
>>>>  		/*
>>>>  		 * Serialize via hugetlb_fault_mutex
>>>> @@ -273,7 +273,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
>>>>  		mutex_lock(&hugetlb_fault_mutex_table[hash]);
>>>>  
>>>>  		err = -ENOMEM;
>>>> -		dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
>>>> +		dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize);
>>>>  		if (!dst_pte) {
>>>>  			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
>>>>  			goto out_unlock;
>>>> @@ -300,7 +300,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
>>>>  
>>>>  			err = copy_huge_page_from_user(page,
>>>>  						(const void __user *)src_addr,
>>>> -						pages_per_huge_page(h), true);
>>>> +						vma_hpagesize / PAGE_SIZE,
>>>> +						true);
>>>>  			if (unlikely(err)) {
>>>>  				err = -EFAULT;
>>>>  				goto out;
>>>
>>> Looks right.
>>>
>>> We could go ahead and remove local variable `h', given that
>>> hugetlb_fault_mutex_hash() doesn't actually use its first arg..
>> 
>> Oops, haven't imagine h is not used in the function.
>> 
>> 
>> Any historical reason to pass h in hugetlb_fault_mutex_hash()? Neither these
>> two definition use it.
>
>See 1b426bac66e6 ("hugetlb: use same fault hash key for shared and private
>mappings").  Prior to that change, the hash key for private mappings was
>created by:
>
>	key[0] = (unsigned long) mm;
>	key[1] = address >> huge_page_shift(h);
>
>When removing that code, I should have removed 'h'.

Thanks for this information.

>-- 
>Mike Kravetz

-- 
Wei Yang
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