On 3/23/21 2:52 PM, Jason Gunthorpe wrote:
On Sun, Mar 21, 2021 at 07:45:28PM +0100, Thomas Hellström (Intel) wrote:
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,
}
#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
+/*
+ * If we can't determine whether or not a pte is special, then fail immediately
+ * 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
Yes, you're right. I misread it to refer to the actual code in the
gup_pte_range function rather than to the empty version. I'll move it back.
/Thomas
Jason
