mm/pagewalk: drop FW_MIGRATION

We removed the last user of FW_MIGRATION in commit 912aa825957f ("Revert
"mm/ksm: convert break_ksm() from walk_page_range_vma() to folio_walk"").

So let's remove FW_MIGRATION and assign FW_ZEROPAGE bit 0.  Including
leafops.h is no longer required.

While at it, convert "expose_page" to "zeropage", as zeropages are now the
only remaining use case for not exposing a page.

Link: https://lkml.kernel.org/r/20260227212952.190691-1-david@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 9 insertions, 39 deletions

diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index 88e18615dd72..b41d7265c01b 100644
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -148,14 +148,8 @@ int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
 
 typedef int __bitwise folio_walk_flags_t;
 
-/*
- * Walk migration entries as well. Careful: a large folio might get split
- * concurrently.
- */
-#define FW_MIGRATION			((__force folio_walk_flags_t)BIT(0))
-
 /* Walk shared zeropages (small + huge) as well. */
-#define FW_ZEROPAGE			((__force folio_walk_flags_t)BIT(1))
+#define FW_ZEROPAGE			((__force folio_walk_flags_t)BIT(0))
 
 enum folio_walk_level {
 	FW_LEVEL_PTE,
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index a94c401ab2cf..cb358558807c 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -5,7 +5,6 @@
 #include <linux/hugetlb.h>
 #include <linux/mmu_context.h>
 #include <linux/swap.h>
-#include <linux/leafops.h>
 
 #include <asm/tlbflush.h>
 
@@ -841,9 +840,6 @@ int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
  * VM as documented by vm_normal_page(). If requested, zeropages will be
  * returned as well.
  *
- * As default, this function only considers present page table entries.
- * If requested, it will also consider migration entries.
- *
  * If this function returns NULL it might either indicate "there is nothing" or
  * "there is nothing suitable".
  *
@@ -854,11 +850,10 @@ int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
  * that call.
  *
  * @fw->page will correspond to the page that is effectively referenced by
- * @addr. However, for migration entries and shared zeropages @fw->page is
- * set to NULL. Note that large folios might be mapped by multiple page table
- * entries, and this function will always only lookup a single entry as
- * specified by @addr, which might or might not cover more than a single page of
- * the returned folio.
+ * @addr. However, for shared zeropages @fw->page is set to NULL. Note that
+ * large folios might be mapped by multiple page table entries, and this
+ * function will always only lookup a single entry as specified by @addr, which
+ * might or might not cover more than a single page of the returned folio.
  *
  * This function must *not* be used as a naive replacement for
  * get_user_pages() / pin_user_pages(), especially not to perform DMA or
@@ -885,7 +880,7 @@ struct folio *folio_walk_start(struct folio_walk *fw,
 		folio_walk_flags_t flags)
 {
 	unsigned long entry_size;
-	bool expose_page = true;
+	bool zeropage = false;
 	struct page *page;
 	pud_t *pudp, pud;
 	pmd_t *pmdp, pmd;
@@ -933,10 +928,6 @@ struct folio *folio_walk_start(struct folio_walk *fw,
 			if (page)
 				goto found;
 		}
-		/*
-		 * TODO: FW_MIGRATION support for PUD migration entries
-		 * once there are relevant users.
-		 */
 		spin_unlock(ptl);
 		goto not_found;
 	}
@@ -970,16 +961,9 @@ pmd_table:
 			} else if ((flags & FW_ZEROPAGE) &&
 				    is_huge_zero_pmd(pmd)) {
 				page = pfn_to_page(pmd_pfn(pmd));
-				expose_page = false;
+				zeropage = true;
 				goto found;
 			}
-		} else if ((flags & FW_MIGRATION) &&
-			   pmd_is_migration_entry(pmd)) {
-			const softleaf_t entry = softleaf_from_pmd(pmd);
-
-			page = softleaf_to_page(entry);
-			expose_page = false;
-			goto found;
 		}
 		spin_unlock(ptl);
 		goto not_found;
@@ -1004,15 +988,7 @@ pte_table:
 		if ((flags & FW_ZEROPAGE) &&
 		    is_zero_pfn(pte_pfn(pte))) {
 			page = pfn_to_page(pte_pfn(pte));
-			expose_page = false;
-			goto found;
-		}
-	} else if (!pte_none(pte)) {
-		const softleaf_t entry = softleaf_from_pte(pte);
-
-		if ((flags & FW_MIGRATION) && softleaf_is_migration(entry)) {
-			page = softleaf_to_page(entry);
-			expose_page = false;
+			zeropage = true;
 			goto found;
 		}
 	}
@@ -1021,7 +997,7 @@ not_found:
 	vma_pgtable_walk_end(vma);
 	return NULL;
 found:
-	if (expose_page)
+	if (!zeropage)
 		/* Note: Offset from the mapped page, not the folio start. */
 		fw->page = page + ((addr & (entry_size - 1)) >> PAGE_SHIFT);
 	else