arm64/mm: Check pmd_table() in pmd_trans_huge()

Check for pmd_table() in pmd_trans_huge() rather then just checking for the
PMD_TABLE_BIT. But ensure all present-invalid entries are handled correctly
by always setting PTE_VALID before checking with pmd_table().

Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250221044227.1145393-8-anshuman.khandual@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: Ryan Roberts

arch/arm64/include/asm/pgtable.h

@@ -548,18 +548,6 @@ static inline int pmd_protnone(pmd_t pmd)
 #endif
 
 #define pmd_present(pmd)	pte_present(pmd_pte(pmd))
-
-/*
- * THP definitions.
- */
-
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-static inline int pmd_trans_huge(pmd_t pmd)
-{
-	return pmd_val(pmd) && pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
-}
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
-
 #define pmd_dirty(pmd)		pte_dirty(pmd_pte(pmd))
 #define pmd_young(pmd)		pte_young(pmd_pte(pmd))
 #define pmd_valid(pmd)		pte_valid(pmd_pte(pmd))
@@ -746,6 +734,18 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 #define pmd_leaf_size(pmd)	(pmd_cont(pmd) ? CONT_PMD_SIZE : PMD_SIZE)
 #define pte_leaf_size(pte)	(pte_cont(pte) ? CONT_PTE_SIZE : PAGE_SIZE)
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline int pmd_trans_huge(pmd_t pmd)
+{
+	/*
+	 * If pmd is present-invalid, pmd_table() won't detect it
+	 * as a table, so force the valid bit for the comparison.
+	 */
+	return pmd_val(pmd) && pmd_present(pmd) &&
+	       !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID));
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 #if defined(CONFIG_ARM64_64K_PAGES) || CONFIG_PGTABLE_LEVELS < 3
 static inline bool pud_sect(pud_t pud) { return false; }
 static inline bool pud_table(pud_t pud) { return true; }