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, 15 insertions, 16 deletions

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index be20468fb5a9..a4e23818f37f 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -16,6 +16,7 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw)
 static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
 		    spinlock_t **ptlp)
 {
+	bool is_migration;
 	pte_t ptent;
 
 	if (pvmw->flags & PVMW_SYNC) {
@@ -26,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
 		return !!pvmw->pte;
 	}
 
+	is_migration = pvmw->flags & PVMW_MIGRATION;
 again:
 	/*
 	 * It is important to return the ptl corresponding to pte,
@@ -41,11 +43,14 @@ again:
 
 	ptent = ptep_get(pvmw->pte);
 
-	if (pvmw->flags & PVMW_MIGRATION) {
-		if (!is_swap_pte(ptent))
+	if (pte_none(ptent)) {
+		return false;
+	} else if (pte_present(ptent)) {
+		if (is_migration)
 			return false;
-	} else if (is_swap_pte(ptent)) {
+	} else if (!is_migration) {
 		swp_entry_t entry;
+
 		/*
 		 * Handle un-addressable ZONE_DEVICE memory.
 		 *
@@ -66,8 +71,6 @@ again:
 		if (!is_device_private_entry(entry) &&
 		    !is_device_exclusive_entry(entry))
 			return false;
-	} else if (!pte_present(ptent)) {
-		return false;
 	}
 	spin_lock(*ptlp);
 	if (unlikely(!pmd_same(*pmdvalp, pmdp_get_lockless(pvmw->pmd)))) {
@@ -113,21 +116,17 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 			return false;
 
 		pfn = softleaf_to_pfn(entry);
-	} else if (is_swap_pte(ptent)) {
-		swp_entry_t entry;
+	} else if (pte_present(ptent)) {
+		pfn = pte_pfn(ptent);
+	} else {
+		const softleaf_t entry = softleaf_from_pte(ptent);
 
 		/* Handle un-addressable ZONE_DEVICE memory */
-		entry = pte_to_swp_entry(ptent);
-		if (!is_device_private_entry(entry) &&
-		    !is_device_exclusive_entry(entry))
-			return false;
-
-		pfn = swp_offset_pfn(entry);
-	} else {
-		if (!pte_present(ptent))
+		if (!softleaf_is_device_private(entry) &&
+		    !softleaf_is_device_exclusive(entry))
 			return false;
 
-		pfn = pte_pfn(ptent);
+		pfn = softleaf_to_pfn(entry);
 	}
 
 	if ((pfn + pte_nr - 1) < pvmw->pfn)