linux-kernel - Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic

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Date:   Thu, 14 Jul 2022 11:52:18 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, mike.kravetz@...cle.com,
        songmuchun@...edance.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Axel Rasmussen <axelrasmussen@...gle.com>
Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in
 hugetlb_mcopy_atomic_pte

On Thu, Jul 14, 2022 at 05:59:53PM +0800, Miaohe Lin wrote:
> On 2022/7/14 1:23, Andrew Morton wrote:
> > On Tue, 12 Jul 2022 21:05:42 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> > 
> >> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page
> >> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called
> >> for them mistakenly because they're not vm_shared. This will corrupt the
> >> page->mapping used by page cache code.
> > 
> > Well that sounds bad.  And theories on why this has gone unnoticed for
> > over a year?  I assume this doesn't have coverage in our selftests?
> 
> As discussed in another thread, when minor fault handling is proposed, only
> VM_SHARED vma is expected to be supported. And the test case is also missing.

Yes, after this patch applied it'll be great to have the test case covering
private mappings too.

It's just that it'll be a bit more than setting test_uffdio_minor=1 for
"hugetlb" test.  In hugetlb_allocate_area() we'll need to setup the alias
too for !shared case, it'll be a bit challenging since currently we're
using anonymous hugetlb mappings for private tests, and I'm not sure
whether we'll need the hugetlb path back just like what we have with
"hugetlb_shared" tests.

-- 
Peter Xu