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Date:   Mon, 14 Nov 2022 11:30:12 -0800
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Peter Xu <peterx@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Chen <harperchen1110@gmail.com>, stable@vger.kernel.org
Subject: Re: [PATCH v9 2/3] hugetlb: remove duplicate mmu notifications
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References: <20221111232628.290160-1-mike.kravetz@oracle.com>
 <20221111232628.290160-3-mike.kravetz@oracle.com>
 <cfb2e9de-3bf8-6380-f336-dc3d7a5ecc29@redhat.com>
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On 11/14/22 10:06, David Hildenbrand wrote:
> On 12.11.22 00:26, Mike Kravetz wrote:
> > The common hugetlb unmap routine __unmap_hugepage_range performs mmu
> > notification calls.  However, in the case where __unmap_hugepage_range
> > is called via __unmap_hugepage_range_final, mmu notification calls are
> > performed earlier in other calling routines.
> > 
> > Remove mmu notification calls from __unmap_hugepage_range.  Add
> > notification calls to the only other caller: unmap_hugepage_range.
> > unmap_hugepage_range is called for truncation and hole punch, so
> > change notification type from UNMAP to CLEAR as this is more appropriate.
> > 
> > Fixes: 90e7e7f5ef3f ("mm: enable MADV_DONTNEED for hugetlb mappings")
> > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> > Reported-by: Wei Chen <harperchen1110@gmail.com>
> > Cc: <stable@vger.kernel.org>
> 
> Why exactly do we care about stable backports here? What's the user-visible
> impact?

I do not believe the duplicate notification calls have a user-visible impact.
They have existed for a long time without notice.

When fixing this issue, this was noticed and cleaned up.  We should be able to
fix the issue without this change.  Unless someone really thinks this needs
to be fixed in stable as well.

I will move this to the end of the patch series and drop the Fixes/Cc stable
tags.  Will send out later today as I will want to do another round of testing.
-- 
Mike Kravetz