mm: avoid unnecessary uses of is_swap_pte()

There's an established convention in the kernel that we treat PTEs as
containing swap entries (and the unfortunately named non-swap swap
entries) should they be neither empty (i.e.  pte_none() evaluating true)
nor present (i.e.  pte_present() evaluating true).

However, there is some inconsistency in how this is applied, as we also
have the is_swap_pte() helper which explicitly performs this check:

	/* check whether a pte points to a swap entry */
	static inline int is_swap_pte(pte_t pte)
	{
		return !pte_none(pte) && !pte_present(pte);
	}

As this represents a predicate, and it's logical to assume that in order
to establish that a PTE entry can correctly be manipulated as a
swap/non-swap entry, this predicate seems as if it must first be checked.

But we instead, we far more often utilise the established convention of
checking pte_none() / pte_present() before operating on entries as if they
were swap/non-swap.

This patch works towards correcting this inconsistency by removing all
uses of is_swap_pte() where we are already in a position where we perform
pte_none()/pte_present() checks anyway or otherwise it is clearly logical
to do so.

We also take advantage of the fact that pte_swp_uffd_wp() is only set on
swap entries.

Additionally, update comments referencing to is_swap_pte() and
non_swap_entry().

No functional change intended.

Link: https://lkml.kernel.org/r/17fd6d7f46a846517fd455fadd640af47fcd7c55.1762812360.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/mm/mremap.c b/mm/mremap.c
index 7c21b2ad13f6..62b6827abacf 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -158,6 +158,9 @@ static void drop_rmap_locks(struct vm_area_struct *vma)
 
 static pte_t move_soft_dirty_pte(pte_t pte)
 {
+	if (pte_none(pte))
+		return pte;
+
 	/*
 	 * Set soft dirty bit so we can notice
 	 * in userspace the ptes were moved.
@@ -165,7 +168,7 @@ static pte_t move_soft_dirty_pte(pte_t pte)
 #ifdef CONFIG_MEM_SOFT_DIRTY
 	if (pte_present(pte))
 		pte = pte_mksoft_dirty(pte);
-	else if (is_swap_pte(pte))
+	else
 		pte = pte_swp_mksoft_dirty(pte);
 #endif
 	return pte;
@@ -294,7 +297,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
 			if (need_clear_uffd_wp) {
 				if (pte_present(pte))
 					pte = pte_clear_uffd_wp(pte);
-				else if (is_swap_pte(pte))
+				else
 					pte = pte_swp_clear_uffd_wp(pte);
 			}
 			set_ptes(mm, new_addr, new_ptep, pte, nr_ptes);