diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ff74aa53842e..7f21de55d6ac 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2535,6 +2535,14 @@ config MITIGATION_ADDRESS_SPACE_ISOLATION
 	  This dependencies will later be removed with extensions to the KASAN
 	  implementation.
 
+config ADDRESS_SPACE_ISOLATION_DEFAULT_ON
+	bool "Enable address space isolation by default"
+	default n
+	depends on ADDRESS_SPACE_ISOLATION
+	help
+	  If selected, ASI is enabled by default at boot if the asi=on or
+	  asi=off are not specified.
+
 config MITIGATION_RETPOLINE
 	bool "Avoid speculative indirect branches in kernel"
 	select OBJTOOL if HAVE_OBJTOOL
diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index a052e561b2b7..04ba2ec7fd28 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -6,6 +6,7 @@
 
 #include <asm/pgtable_types.h>
 #include <asm/percpu.h>
+#include <asm/cpufeature.h>
 #include <asm/processor.h>
 #include <linux/sched.h>
 
@@ -64,6 +65,9 @@
  * the N ASI classes.
  */
 
+/* Try to avoid this outside of hot code (see comment on _static_cpu_has). */
+#define static_asi_enabled() cpu_feature_enabled(X86_FEATURE_ASI)
+
 #define ASI_MAX_NUM_ORDER	2
 #define ASI_MAX_NUM		(1 << ASI_MAX_NUM_ORDER)
 
@@ -101,6 +105,8 @@ struct asi {
 
 DECLARE_PER_CPU_ALIGNED(struct asi *, curr_asi);
 
+void asi_check_boottime_disable(void);
+
 void asi_init_mm_state(struct mm_struct *mm);
 
 int  asi_register_class(const char *name, const struct asi_hooks *ops);
@@ -124,7 +130,9 @@ void asi_exit(void);
 /* The target is the domain we'll enter when returning to process context. */
 static __always_inline struct asi *asi_get_target(struct task_struct *p)
 {
-	return p->thread.asi_state.target;
+	return static_asi_enabled()
+	       ? p->thread.asi_state.target
+	       : NULL;
 }
 
 static __always_inline void asi_set_target(struct task_struct *p,
@@ -135,7 +143,9 @@ static __always_inline void asi_set_target(struct task_struct *p,
 
 static __always_inline struct asi *asi_get_current(void)
 {
-	return this_cpu_read(curr_asi);
+	return static_asi_enabled()
+	       ? this_cpu_read(curr_asi)
+	       : NULL;
 }
 
 /* Are we currently in a restricted address space? */
@@ -144,7 +154,11 @@ static __always_inline bool asi_is_restricted(void)
 	return (bool)asi_get_current();
 }
 
-/* If we exit/have exited, can we stay that way until the next asi_enter? */
+/*
+ * If we exit/have exited, can we stay that way until the next asi_enter?
+ *
+ * When ASI is disabled, this returns true.
+ */
 static __always_inline bool asi_is_relaxed(void)
 {
 	return !asi_get_target(current);
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 3c7434329661..a6b213c7df44 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -470,6 +470,7 @@
 #define X86_FEATURE_BHI_CTRL		(21*32+ 2) /* "" BHI_DIS_S HW control available */
 #define X86_FEATURE_CLEAR_BHB_HW	(21*32+ 3) /* "" BHI_DIS_S HW control enabled */
 #define X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT (21*32+ 4) /* "" Clear branch history at vmexit using SW loop */
+#define X86_FEATURE_ASI			(21*32+5) /* Kernel Address Space Isolation */
 
 /*
  * BUG word(s)
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index c492bdc97b05..c7964ed4fef8 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -50,6 +50,12 @@
 # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
 #endif
 
+#ifdef CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION
+# define DISABLE_ASI		0
+#else
+# define DISABLE_ASI		(1 << (X86_FEATURE_ASI & 31))
+#endif
+
 #ifdef CONFIG_MITIGATION_RETPOLINE
 # define DISABLE_RETPOLINE	0
 #else
@@ -154,7 +160,7 @@
 #define DISABLED_MASK17	0
 #define DISABLED_MASK18	(DISABLE_IBT)
 #define DISABLED_MASK19	(DISABLE_SEV_SNP)
-#define DISABLED_MASK20	0
+#define DISABLED_MASK20	(DISABLE_ASI)
 #define DISABLED_MASK21	0
 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 22)
 
diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index c5979d78fdbb..21207a3e8b17 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -4,7 +4,9 @@
 #include <linux/percpu.h>
 #include <linux/spinlock.h>
 
+#include <linux/init.h>
 #include <asm/asi.h>
+#include <asm/cmdline.h>
 #include <asm/pgalloc.h>
 #include <asm/mmu_context.h>
 
@@ -28,6 +30,9 @@ int asi_register_class(const char *name, const struct asi_hooks *ops)
 {
 	int i;
 
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return 0;
+
 	VM_BUG_ON(name == NULL);
 
 	spin_lock(&asi_class_lock);
@@ -52,6 +57,9 @@ EXPORT_SYMBOL_GPL(asi_register_class);
 
 void asi_unregister_class(int index)
 {
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return;
+
 	BUG_ON(!asi_index_valid(index));
 
 	spin_lock(&asi_class_lock);
@@ -63,11 +71,36 @@ void asi_unregister_class(int index)
 }
 EXPORT_SYMBOL_GPL(asi_unregister_class);
 
+void __init asi_check_boottime_disable(void)
+{
+	bool enabled = IS_ENABLED(CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION_DEFAULT_ON);
+	char arg[4];
+	int ret;
+
+	ret = cmdline_find_option(boot_command_line, "asi", arg, sizeof(arg));
+	if (ret == 3 && !strncmp(arg, "off", 3)) {
+		enabled = false;
+		pr_info("ASI disabled through kernel command line.\n");
+	} else if (ret == 2 && !strncmp(arg, "on", 2)) {
+		enabled = true;
+		pr_info("Ignoring asi=on param while ASI implementation is incomplete.\n");
+	} else {
+		pr_info("ASI %s by default.\n",
+			enabled ? "enabled" : "disabled");
+	}
+
+	if (enabled)
+		pr_info("ASI enablement ignored due to incomplete implementation.\n");
+}
 
 static void __asi_destroy(struct asi *asi)
 {
-	lockdep_assert_held(&asi->mm->asi_init_lock);
+	WARN_ON_ONCE(asi->ref_count <= 0);
+	if (--(asi->ref_count) > 0)
+		return;
 
+	free_pages((ulong)asi->pgd, PGD_ALLOCATION_ORDER);
+	memset(asi, 0, sizeof(struct asi));
 }
 
 int asi_init(struct mm_struct *mm, int asi_index, struct asi **out_asi)
@@ -77,6 +110,9 @@ int asi_init(struct mm_struct *mm, int asi_index, struct asi **out_asi)
 
 	*out_asi = NULL;
 
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return 0;
+
 	BUG_ON(!asi_index_valid(asi_index));
 
 	asi = &mm->asi[asi_index];
@@ -121,7 +157,7 @@ void asi_destroy(struct asi *asi)
 {
 	struct mm_struct *mm;
 
-	if (!asi)
+	if (!boot_cpu_has(X86_FEATURE_ASI) || !asi)
 		return;
 
 	mm = asi->mm;
@@ -130,11 +166,7 @@ void asi_destroy(struct asi *asi)
 	 * to block concurrent asi_init calls.
 	 */
 	mutex_lock(&mm->asi_init_lock);
-	WARN_ON_ONCE(asi->ref_count <= 0);
-	if (--(asi->ref_count) == 0) {
-		free_pages((ulong)asi->pgd, PGD_ALLOCATION_ORDER);
-		memset(asi, 0, sizeof(struct asi));
-	}
+	__asi_destroy(asi);
 	mutex_unlock(&mm->asi_init_lock);
 }
 EXPORT_SYMBOL_GPL(asi_destroy);
@@ -178,6 +210,9 @@ static noinstr void __asi_enter(void)
 
 noinstr void asi_enter(struct asi *asi)
 {
+	if (!static_asi_enabled())
+		return;
+
 	VM_WARN_ON_ONCE(!asi);
 
 	asi_set_target(current, asi);
@@ -189,8 +224,10 @@ EXPORT_SYMBOL_GPL(asi_enter);
 
 inline_or_noinstr void asi_relax(void)
 {
-	barrier();
-	asi_set_target(current, NULL);
+	if (static_asi_enabled()) {
+		barrier();
+		asi_set_target(current, NULL);
+	}
 }
 EXPORT_SYMBOL_GPL(asi_relax);
 
@@ -199,6 +236,9 @@ noinstr void asi_exit(void)
 	u64 unrestricted_cr3;
 	struct asi *asi;
 
+	if (!static_asi_enabled())
+		return;
+
 	preempt_disable_notrace();
 
 	VM_BUG_ON(this_cpu_read(cpu_tlbstate.loaded_mm) ==
@@ -229,6 +269,9 @@ EXPORT_SYMBOL_GPL(asi_exit);
 
 void asi_init_mm_state(struct mm_struct *mm)
 {
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return;
+
 	memset(mm->asi, 0, sizeof(mm->asi));
 	mutex_init(&mm->asi_init_lock);
 }
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 5b06d30dee67..e2a29f6779d9 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -27,6 +27,7 @@
 #include <asm/text-patching.h>
 #include <asm/memtype.h>
 #include <asm/paravirt.h>
+#include <asm/asi.h>
 
 /*
  * We need to define the tracepoints somewhere, and tlb.c
@@ -250,7 +251,7 @@ static void __init probe_page_size_mask(void)
 	__default_kernel_pte_mask = __supported_pte_mask;
 	/* Except when with PTI where the kernel is mostly non-Global: */
 	if (cpu_feature_enabled(X86_FEATURE_PTI) ||
-	    IS_ENABLED(CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION))
+	    cpu_feature_enabled(X86_FEATURE_ASI))
 		__default_kernel_pte_mask &= ~_PAGE_GLOBAL;
 
 	/* Enable 1 GB linear kernel mappings if available: */
@@ -757,6 +758,7 @@ void __init init_mem_mapping(void)
 	unsigned long end;
 
 	pti_check_boottime_disable();
+	asi_check_boottime_disable();
 	probe_page_size_mask();
 	setup_pcid();
 
diff --git a/include/asm-generic/asi.h b/include/asm-generic/asi.h
index 3660fc1defe8..d0a451f9d0b7 100644
--- a/include/asm-generic/asi.h
+++ b/include/asm-generic/asi.h
@@ -48,6 +48,10 @@ static inline struct asi *asi_get_target(struct task_struct *p) { return NULL; }
 
 static inline pgd_t *asi_pgd(struct asi *asi) { return NULL; }
 
+#define static_asi_enabled() false
+
+static inline void asi_check_boottime_disable(void) { }
+
 #endif  /* !_ASSEMBLY_ */
 
 #endif /* !CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION */
