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    SubjectRe: [PATCH 02/10] mm/hmm: do not erase snapshot when a range is invalidated
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    On 1/29/19 8:54 AM, jglisse@redhat.com wrote:
    > From: Jérôme Glisse <jglisse@redhat.com>
    >
    > Users of HMM might be using the snapshot information to do
    > preparatory step like dma mapping pages to a device before
    > checking for invalidation through hmm_vma_range_done() so
    > do not erase that information and assume users will do the
    > right thing.
    >
    > Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Ralph Campbell <rcampbell@nvidia.com>
    > Cc: John Hubbard <jhubbard@nvidia.com>
    > ---
    > mm/hmm.c | 6 ------
    > 1 file changed, 6 deletions(-)
    >
    > diff --git a/mm/hmm.c b/mm/hmm.c
    > index b9f384ea15e9..74d69812d6be 100644
    > --- a/mm/hmm.c
    > +++ b/mm/hmm.c
    > @@ -170,16 +170,10 @@ static int hmm_invalidate_range(struct hmm *hmm, bool device,
    >
    > spin_lock(&hmm->lock);
    > list_for_each_entry(range, &hmm->ranges, list) {
    > - unsigned long addr, idx, npages;
    > -
    > if (update->end < range->start || update->start >= range->end)
    > continue;
    >
    > range->valid = false;
    > - addr = max(update->start, range->start);
    > - idx = (addr - range->start) >> PAGE_SHIFT;
    > - npages = (min(range->end, update->end) - addr) >> PAGE_SHIFT;
    > - memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
    > }
    > spin_unlock(&hmm->lock);
    >
    >

    Seems harmless to me. I really cannot see how this could cause a problem,
    so you can add:

    Reviewed-by: John Hubbard <jhubbard@nvidia.com>

    thanks,
    --
    John Hubbard
    NVIDIA

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