linux-kernel - Re: [PATCH 0/3] mm/uffd: Fix missing markers on hugetlb

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Date:   Thu, 5 Jan 2023 09:16:43 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        James Houghton <jthoughton@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/3] mm/uffd: Fix missing markers on hugetlb

On 04.01.23 23:52, Peter Xu wrote:
> When James was developing the vma split fix for hugetlb pmd sharing, he
> found that hugetlb uffd-wp is broken with the test case he developed [1]:
> 
> https://lore.kernel.org/r/CADrL8HWSym93=yNpTUdWebOEzUOTR2ffbfUk04XdK6O+PNJNoA@mail.gmail.com
> 
> Missing hugetlb pgtable pages caused uffd-wp to lose message when vma split
> happens to be across a shared huge pmd range in the test.
> 
> The issue is pgtable pre-allocation on hugetlb path was overlooked.  That
> was fixed in patch 1.

Nice timing, I stumbled over that while adjusting background snapshot 
code in QEMU and wondered why we are not allocating page tables in that 
case -- and wanted to ask you why :)

-- 
Thanks,

David / dhildenb