[PATCH v2 01/19] mm: Introduce ARCH_SUPPORTS_HUGE_PFNMAP and special bits to pmd/pud

[Peter Xu <peterx@redhat.com>]

This patch introduces the option to introduce special pte bit into
pmd/puds.  Archs can start to define pmd_special / pud_special when
supported by selecting the new option.  Per-arch support will be added
later.

Before that, create fallbacks for these helpers so that they are always
available.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/linux/mm.h | 24 ++++++++++++++++++++++++
 mm/Kconfig         | 13 +++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b0ff06d18c71..d900f15b7650 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2643,6 +2643,30 @@ static inline pte_t pte_mkspecial(pte_t pte)
 }
 #endif
 
+#ifndef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
+static inline bool pmd_special(pmd_t pmd)
+{
+	return false;
+}
+
+static inline pmd_t pmd_mkspecial(pmd_t pmd)
+{
+	return pmd;
+}
+#endif	/* CONFIG_ARCH_SUPPORTS_PMD_PFNMAP */
+
+#ifndef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
+static inline bool pud_special(pud_t pud)
+{
+	return false;
+}
+
+static inline pud_t pud_mkspecial(pud_t pud)
+{
+	return pud;
+}
+#endif	/* CONFIG_ARCH_SUPPORTS_PUD_PFNMAP */
+
 #ifndef CONFIG_ARCH_HAS_PTE_DEVMAP
 static inline int pte_devmap(pte_t pte)
 {
diff --git a/mm/Kconfig b/mm/Kconfig
index 8078a4b3c509..b23913d4e47e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -875,6 +875,19 @@ endif # TRANSPARENT_HUGEPAGE
 config PGTABLE_HAS_HUGE_LEAVES
 	def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE
 
+# TODO: Allow to be enabled without THP
+config ARCH_SUPPORTS_HUGE_PFNMAP
+	def_bool n
+	depends on TRANSPARENT_HUGEPAGE
+
+config ARCH_SUPPORTS_PMD_PFNMAP
+	def_bool y
+	depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE
+
+config ARCH_SUPPORTS_PUD_PFNMAP
+	def_bool y
+	depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+
 #
 # UP and nommu archs use km based percpu allocator
 #
-- 
2.45.0