@@ -120,6 +120,9 @@ struct asi_taint_policy {
 	asi_taints_t set;
 };
 
+extern struct asi __asi_global_nonsensitive;
+#define ASI_GLOBAL_NONSENSITIVE	(&__asi_global_nonsensitive)
+
 /*
  * An ASI domain (struct asi) represents a restricted address space. The
  * unrestricted address space (and user address space under PTI) are not

@@ -13,6 +13,7 @@
 #include <asm/mmu_context.h>
 #include <asm/traps.h>
 
+#include "mm_internal.h"
 #include "../../../mm/internal.h"
 
 static struct asi_taint_policy *taint_policies[ASI_MAX_NUM_CLASSES];

@@ -26,6 +27,13 @@ const char *asi_class_names[] = {
 DEFINE_PER_CPU_ALIGNED(struct asi *, curr_asi);
 EXPORT_SYMBOL(curr_asi);
 
+static __aligned(PAGE_SIZE) pgd_t asi_global_nonsensitive_pgd[PTRS_PER_PGD];
+
+struct asi __asi_global_nonsensitive = {
+	.pgd = asi_global_nonsensitive_pgd,
+	.mm = &init_mm,
+};
+
 static inline bool asi_class_id_valid(enum asi_class_id class_id)
 {
 	return class_id >= 0 && class_id < ASI_MAX_NUM_CLASSES;

@@ -156,6 +164,31 @@ void __init asi_check_boottime_disable(void)
 		pr_info("ASI enablement ignored due to incomplete implementation.\n");
 }
 
+static int __init asi_global_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return 0;
+
+	/*
+	 * Lower-level pagetables for global nonsensitive mappings are shared,
+	 * but the PGD has to be copied into each domain during asi_init. To
+	 * avoid needing to synchronize new mappings into pre-existing domains
+	 * we just pre-allocate all of the relevant level N-1 entries so that
+	 * the global nonsensitive PGD already has pointers that can be copied
+	 * when new domains get asi_init()ed.
+	 */
+	preallocate_sub_pgd_pages(asi_global_nonsensitive_pgd,
+				  PAGE_OFFSET,
+				  PAGE_OFFSET + PFN_PHYS(max_pfn) - 1,
+				  "ASI Global Non-sensitive direct map");
+	preallocate_sub_pgd_pages(asi_global_nonsensitive_pgd,
+				  VMALLOC_START, VMALLOC_END,
+				  "ASI Global Non-sensitive vmalloc");
+
+	return 0;
+}
+subsys_initcall(asi_global_init)
+
 static void __asi_destroy(struct asi *asi)
 {
 	WARN_ON_ONCE(asi->ref_count <= 0);

@@ -170,6 +203,7 @@ int asi_init(struct mm_struct *mm, enum asi_class_id class_id, struct asi **out_
 {
 	struct asi *asi;
 	int err = 0;
+	uint i;
 
 	*out_asi = NULL;
 

@@ -203,6 +237,9 @@ int asi_init(struct mm_struct *mm, enum asi_class_id class_id, struct asi **out_
 	asi->mm = mm;
 	asi->class_id = class_id;
 
+	for (i = KERNEL_PGD_BOUNDARY; i < PTRS_PER_PGD; i++)
+		set_pgd(asi->pgd + i, asi_global_nonsensitive_pgd[i]);
+
 exit_unlock:
 	if (err)
 		__asi_destroy(asi);

@@ -1288,18 +1288,15 @@ static void __init register_page_bootmem_info(void)
 #endif
 }
 
-/*
- * Pre-allocates page-table pages for the vmalloc area in the kernel page-table.
- * 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)
+/* Initialize empty pagetables at the level below PGD.  */
+void __init preallocate_sub_pgd_pages(pgd_t *pgd_table, ulong start,
+				      ulong end, const char *name)
 {
 	unsigned long addr;
 	const char *lvl;
 
-	for (addr = VMALLOC_START; addr <= VMEMORY_END; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
-		pgd_t *pgd = pgd_offset_k(addr);
+	for (addr = start; addr <= end; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
+		pgd_t *pgd = pgd_offset_pgd(pgd_table, addr);
 		p4d_t *p4d;
 		pud_t *pud;
 

@@ -1335,7 +1332,17 @@ static void __init preallocate_vmalloc_pages(void)
 	 * The pages have to be there now or they will be missing in
 	 * process page-tables later.
 	 */
-	panic("Failed to pre-allocate %s pages for vmalloc area\n", lvl);
+	panic("Failed to pre-allocate %s pages for %s area\n", lvl, name);
+}
+
+/*
+ * Pre-allocates page-table pages for the vmalloc area in the kernel page-table.
+ * 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)
+{
+	preallocate_sub_pgd_pages(init_mm.pgd, VMALLOC_START, VMEMORY_END, "vmalloc");
 }
 
 void __init mem_init(void)

@@ -25,4 +25,7 @@ void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
 
 extern unsigned long tlb_single_page_flush_ceiling;
 
+extern void preallocate_sub_pgd_pages(pgd_t *pgd_table, ulong start,
+				      ulong end, const char *name);
+
 #endif	/* __X86_MM_INTERNAL_H */

@@ -23,6 +23,8 @@ typedef u8 asi_taints_t;
 
 #ifndef CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION
 
+#define ASI_GLOBAL_NONSENSITIVE		NULL
+
 struct asi_hooks {};
 struct asi {};