Re: [PATCH] hugetlb: fix huge_pmd_unshare address update

[Muchun Song <songmuchun@bytedance.com>]

On Tue, May 24, 2022 at 01:50:03PM -0700, Mike Kravetz wrote:
> The routine huge_pmd_unshare is passed a pointer to an address
> associated with an area which may be unshared.  If unshare is successful
> this address is updated to 'optimize' callers iterating over huge page
> addresses.  For the optimization to work correctly, address should be
> updated to the last huge page in the unmapped/unshared area.  However,
> in the common case where the passed address is PUD_SIZE aligned, the
> address is incorrectly updated to the address of the preceding huge
> page.  That wastes CPU cycles as the unmapped/unshared range is scanned
> twice.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: 39dde65c9940 ("shared page table for hugetlb page")
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Muchun Song <songmuchun@bytedance.com>

Thanks.