linux-kernel - Re: [PATCH v1 5/5] mm, hwpoison: enable memory error handling on 1GB hugepage

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Date:   Thu, 9 Jun 2022 19:28:25 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
CC:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v1 5/5] mm, hwpoison: enable memory error handling on 1GB
 hugepage

On 2022/6/9 16:45, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Jun 08, 2022 at 08:57:24PM +0800, Miaohe Lin wrote:
> ...
>>>
>>> I think that most of page table walker for user address space should first
>>> check is_vm_hugetlb_page() and call hugetlb specific walking code for vma
>>> with VM_HUGETLB.
>>> copy_page_range() is a good example.  It calls copy_hugetlb_page_range()
>>> for vma with VM_HUGETLB and the function should support hwpoison entry.
>>> But I feel that I need testing for confirmation.
>>
>> Sorry, I missed it should be called from hugetlb variants.
>>
>>>
>>> And I'm not sure that all other are prepared for non-present pud-mapping,
>>> so I'll need somehow code inspection and testing for each.
>>
>> I browsed the code again, there still might be some problematic code paths:
>>
>> 1.For follow_pud_mask, !pud_present will mostly reach follow_pmd_mask(). This can be
>> called for hugetlb page. (Note gup_pud_range is fixed at 15494520b776 ("mm: fix gup_pud_range"))
>>
>> 2.Even for huge_pte_alloc, pud_offset will be called in pud_alloc. So pudp will be an invalid pointer.
>> And it will be de-referenced later.
> 
> Yes, these paths need to support non-present pud entry, so I'll update/add
> the patches.  It seems that I did the similar work for pmd few years ago
> (cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present hugepage").

Yes, these should be similar work. Thanks for your hard work. :)

> 
> Thanks,
> Naoya Horiguchi
>