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identity=mailfrom; envelope-from=""; helo=NAM12-MW2-obe.outbound.protection.outlook.com; client-ip=40.107.244.84 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616507540-80050 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Mar 21, 2021 at 07:45:28PM +0100, Thomas Hellstr=C3=B6m (Intel) w= rote: > diff --git a/mm/gup.c b/mm/gup.c > index e40579624f10..1b6a127f0bdd 100644 > +++ b/mm/gup.c > @@ -1993,6 +1993,17 @@ static void __maybe_unused undo_dev_pagemap(int = *nr, int nr_start, > } > =20 > #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL > +/* > + * If we can't determine whether or not a pte is special, then fail im= mediately > + * for ptes. Note, we can still pin HugeTLB as it is guaranteed not to= be > + * special. For THP, special huge entries are indicated by xxx_devmap(= ) > + * returning true, but a corresponding call to get_dev_pagemap() will > + * return NULL. > + * > + * For a futex to be placed on a THP tail page, get_futex_key requires= a > + * get_user_pages_fast_only implementation that can pin pages. Thus it= 's still > + * useful to have gup_huge_pmd even if we can't operate on ptes. > + */ Why move this comment? I think it was correct where it was Jason