mm/swapops: make is_pmd_migration_entry more strict

mainline inclusion
from mainline-v5.19-rc1
commit b304c6f0
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB
CVE: NA

--------------------------------

A pmd migration entry should first be a swap pmd,so use is_swap_pmd(pmd)
instead of !pmd_present(pmd).

On the other hand, some architecture (MIPS for example) may misjudge a
pmd_none entry as a pmd migration entry.

Change-Id: I5e4a32f740adca7a8a2c719b6fc5b0d072e0d3e2
Link: https://lkml.kernel.org/r/1651131333-6386-1-git-send-email-zhanghongchen@loongson.cn


Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>