Re: [PATCH] hugetlb: fix pages per hugetlb calculation

[Matthew Wilcox]

On Mon, Jun 29, 2020 at 11:50:03AM -0700, Mike Kravetz wrote:
> The routine hpage_nr_pages() was incorrectly used to calculate the
> number of base pages in a hugetlb page.  hpage_nr_pages is designed
> to be called for THP pages and will return HPAGE_PMD_NR for hugetlb
> pages of any size.
> 
> Due to the context in which hpage_nr_pages was called, it is unlikely
> to produce a user visible error.  The routine with the incorrect call
> is only exercised in the case of hugetlb memory error or migration.
> In addition, this would need to be on an architecture which supports
> huge page sizes less than PMD_SIZE.  And, the vma containing the huge
> page would also need to smaller than PMD_SIZE.
> 
> Fixes: c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Inadvertently-Reported-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>