mm: add utility functions for ptdesc

Introduce utility functions setting the foundation for ptdescs.  These
will also assist in the splitting out of ptdesc from struct page.

Functions that focus on the descriptor are prefixed with ptdesc_* while
functions that focus on the pagetable are prefixed with pagetable_*.

pagetable_alloc() is defined to allocate new ptdesc pages as compound
pages.  This is to standardize ptdescs by allowing for one allocation and
one free function, in contrast to 2 allocation and 2 free functions.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Vishal Moola (Oracle) <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Claudio Imbrenda <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

2 files changed, 73 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c63ec57a54dc..f75058783359 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2772,6 +2772,57 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
 }
 #endif /* CONFIG_MMU */
 
+static inline struct ptdesc *virt_to_ptdesc(const void *x)
+{
+	return page_ptdesc(virt_to_page(x));
+}
+
+static inline void *ptdesc_to_virt(const struct ptdesc *pt)
+{
+	return page_to_virt(ptdesc_page(pt));
+}
+
+static inline void *ptdesc_address(const struct ptdesc *pt)
+{
+	return folio_address(ptdesc_folio(pt));
+}
+
+static inline bool pagetable_is_reserved(struct ptdesc *pt)
+{
+	return folio_test_reserved(ptdesc_folio(pt));
+}
+
+/**
+ * pagetable_alloc - Allocate pagetables
+ * @gfp:    GFP flags
+ * @order:  desired pagetable order
+ *
+ * pagetable_alloc allocates memory for page tables as well as a page table
+ * descriptor to describe that memory.
+ *
+ * Return: The ptdesc describing the allocated page tables.
+ */
+static inline struct ptdesc *pagetable_alloc(gfp_t gfp, unsigned int order)
+{
+	struct page *page = alloc_pages(gfp | __GFP_COMP, order);
+
+	return page_ptdesc(page);
+}
+
+/**
+ * pagetable_free - Free pagetables
+ * @pt:	The page table descriptor
+ *
+ * pagetable_free frees the memory of all page tables described by a page
+ * table descriptor and the memory for the descriptor itself.
+ */
+static inline void pagetable_free(struct ptdesc *pt)
+{
+	struct page *page = ptdesc_page(pt);
+
+	__free_pages(page, compound_order(page));
+}
+
 #if USE_SPLIT_PTE_PTLOCKS
 #if ALLOC_SPLIT_PTLOCKS
 void __init ptlock_cache_init(void);
@@ -2898,6 +2949,11 @@ static inline struct page *pmd_pgtable_page(pmd_t *pmd)
 	return virt_to_page((void *)((unsigned long) pmd & mask));
 }
 
+static inline struct ptdesc *pmd_ptdesc(pmd_t *pmd)
+{
+	return page_ptdesc(pmd_pgtable_page(pmd));
+}
+
 static inline spinlock_t *pmd_lockptr(struct mm_struct *mm, pmd_t *pmd)
 {
 	return ptlock_ptr(pmd_pgtable_page(pmd));
@@ -3010,6 +3066,11 @@ static inline void mark_page_reserved(struct page *page)
 	adjust_managed_page_count(page, -1);
 }
 
+static inline void free_reserved_ptdesc(struct ptdesc *pt)
+{
+	free_reserved_page(ptdesc_page(pt));
+}
+
 /*
  * Default method to free all the __init memory into the buddy system.
  * The freed pages will be poisoned with pattern "poison" if it's within
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index d4ebcefe482e..c57e940e60d0 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -467,6 +467,18 @@ TABLE_MATCH(memcg_data, pt_memcg_data);
 #undef TABLE_MATCH
 static_assert(sizeof(struct ptdesc) <= sizeof(struct page));
 
+#define ptdesc_page(pt)			(_Generic((pt),			\
+	const struct ptdesc *:		(const struct page *)(pt),	\
+	struct ptdesc *:		(struct page *)(pt)))
+
+#define ptdesc_folio(pt)		(_Generic((pt),			\
+	const struct ptdesc *:		(const struct folio *)(pt),	\
+	struct ptdesc *:		(struct folio *)(pt)))
+
+#define page_ptdesc(p)			(_Generic((p),			\
+	const struct page *:		(const struct ptdesc *)(p),	\
+	struct page *:			(struct ptdesc *)(p)))
+
 /*
  * Used for sizing the vmemmap region on some architectures
  */