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Message-ID: <b6b428a9-f411-a813-0f9f-11b7b57f64c1@redhat.com>
Date:   Thu, 5 Jan 2023 09:16:43 +0100
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Subject: Re: [PATCH 0/3] mm/uffd: Fix missing markers on hugetlb
To:     Peter Xu <peterx@redhat.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        James Houghton <jthoughton@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20230104225207.1066932-1-peterx@redhat.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230104225207.1066932-1-peterx@redhat.com>
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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