[PATCH RFC 05/18] x86/mm/pat: use a generic helper for the large page size

[Mike Rapoport (Microsoft)]

__should_split_large_page() uses x86 specific page_level_size() to
calculate the size and mask of the large page.

In preparation to moving core parts of change_page_attr() to common
code, introduce generic pgtable_level_size() and pgtable_level_mask()
helpers and use them in __should_split_large_page().

No functional change intended.

Assisted-by: Copilot:claude-opus-4.8
Signed-off-by: Mike Rapoport (Microsoft) <rppt at kernel.org>
---
 arch/x86/mm/pat/set_memory.c |  4 ++--
 include/linux/pgtable.h      | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 8a1782f5de3e..ee40962d4ee9 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -956,8 +956,8 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
 		return -EINVAL;
 	}
 
-	psize = page_level_size(level);
-	pmask = page_level_mask(level);
+	psize = pgtable_level_size(level);
+	pmask = pgtable_level_mask(level);
 
 	/*
 	 * Calculate the number of pages, which fit into this large
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 4b42ac5c27d9..9eb00ad6d5d2 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -2364,6 +2364,28 @@ static inline const char *pgtable_level_to_str(enum pgtable_level level)
 	}
 }
 
+/* Size of the memory mapped by a single leaf entry at @level */
+static inline unsigned long pgtable_level_size(enum pgtable_level level)
+{
+	switch (level) {
+	case PGTABLE_LEVEL_PTE:
+		return PAGE_SIZE;
+	case PGTABLE_LEVEL_PMD:
+		return PMD_SIZE;
+	case PGTABLE_LEVEL_PUD:
+		return PUD_SIZE;
+	case PGTABLE_LEVEL_P4D:
+		return P4D_SIZE;
+	default:
+		return PGDIR_SIZE;
+	}
+}
+
+static inline unsigned long pgtable_level_mask(enum pgtable_level level)
+{
+	return ~(pgtable_level_size(level) - 1);
+}
+
 #endif /* !__ASSEMBLY__ */
 
 #if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)

-- 
2.53.0