When separately allocating ptdesc from struct page, calling
preallocate_vmalloc_pages() from mem_init() is too early as the slab
allocator hasn't been set up yet.  Move preallocate_vmalloc_pages() to
vmalloc_init() which is called after the slab allocator has been set up.

Honestly, this patch is a bit bobbins and I'm sure it'll be reworked
before it goes upstream.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 arch/x86/mm/init_64.c |  4 +---
 include/linux/mm.h    | 33 +++++++++++++++++++++++++++++++--
 mm/vmalloc.c          |  2 ++
 3 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 0e4270e20fad..5270fc24f6f6 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1322,7 +1322,7 @@ static void __init register_page_bootmem_info(void)
  * Only the level which needs to be synchronized between all page-tables is
  * allocated because the synchronization can be expensive.
  */
-static void __init preallocate_vmalloc_pages(void)
+void __init preallocate_vmalloc_pages(void)
 {
 	unsigned long addr;
 	const char *lvl;
@@ -1390,8 +1390,6 @@ void __init mem_init(void)
 	/* Register memory areas for /proc/kcore */
 	if (get_gate_vma(&init_mm))
 		kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR, PAGE_SIZE, KCORE_USER);
-
-	preallocate_vmalloc_pages();
 }
 
 int kernel_set_to_readonly;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index edcb7d75542f..e60b181da3df 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1160,6 +1160,12 @@ static inline int is_vmalloc_or_module_addr(const void *x)
 }
 #endif
 
+#ifdef CONFIG_X86
+void __init preallocate_vmalloc_pages(void);
+#else
+static inline void preallocate_vmalloc_pages(void) { }
+#endif
+
 /*
  * How many times the entire folio is mapped as a single unit (eg by a
  * PMD or PUD entry).  This is probably not what you want, except for
@@ -2939,9 +2945,32 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
 }
 #endif /* CONFIG_MMU */
 
+static inline struct page *ptdesc_page(const struct ptdesc *pt)
+{
+	return pt->pt_page;
+}
+
+static inline struct ptdesc *page_ptdesc(const struct page *page)
+{
+	memdesc_t memdesc = READ_ONCE(page->memdesc);
+
+	if (memdesc_type(memdesc) != MEMDESC_TYPE_PAGE_TABLE) {
+		printk(KERN_EMERG "memdesc %lx index %lx\n", memdesc.v, page->__folio_index);
+		VM_BUG_ON_PAGE(1, page);
+		return NULL;
+	}
+	return (void *)(memdesc.v - MEMDESC_TYPE_PAGE_TABLE);
+}
+
+/**
+ * enum pt_flags = How the ptdesc flags bits are used.
+ * @PT_reserved: Used by PowerPC
+ *
+ * The pt flags are stored in a memdesc_flags_t.
+ * The high bits are used for information like zone/node/section.
+ */
 enum pt_flags {
 	PT_reserved = PG_reserved,
-	/* High bits are used for zone/node/section */
 };
 
 static inline struct ptdesc *virt_to_ptdesc(const void *x)
@@ -2957,7 +2986,7 @@ static inline struct ptdesc *virt_to_ptdesc(const void *x)
  */
 static inline void *ptdesc_address(const struct ptdesc *pt)
 {
-	return folio_address(ptdesc_folio(pt));
+	return page_address(pt->pt_page);
 }
 
 static inline bool pagetable_is_reserved(struct ptdesc *pt)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 798b2ed21e46..9b349051a83a 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -5264,6 +5264,8 @@ void __init vmalloc_init(void)
 	struct vm_struct *tmp;
 	int i;
 
+	preallocate_vmalloc_pages();
+
 	/*
 	 * Create the cache for vmap_area objects.
 	 */
-- 
2.47.2