arch/arm64/mm/context.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Based on arch/arm/mm/context.c
  *
  * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
  * Copyright (C) 2012 ARM Ltd.
  */

 #include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/mm.h>

 #include <asm/cpufeature.h>
 #include <asm/mmu_context.h>
 #include <asm/smp.h>
 #include <asm/tlbflush.h>

 static u32 asid_bits;
 static DEFINE_RAW_SPINLOCK(cpu_asid_lock);

 static atomic64_t asid_generation;
 static unsigned long *asid_map;

 static DEFINE_PER_CPU(atomic64_t, active_asids);
 static DEFINE_PER_CPU(u64, reserved_asids);
 static cpumask_t tlb_flush_pending;

 static unsigned long max_pinned_asids;
 static unsigned long nr_pinned_asids;
 static unsigned long *pinned_asid_map;

 #define ASID_MASK		(~GENMASK(asid_bits - 1, 0))
 #define ASID_FIRST_VERSION	(1UL << asid_bits)

 #define NUM_USER_ASIDS		ASID_FIRST_VERSION
 #define asid2idx(asid)		((asid) & ~ASID_MASK)
 #define idx2asid(idx)		asid2idx(idx)

 /* Get the ASIDBits supported by the current CPU */
 static u32 get_cpu_asid_bits(void)
 {
 	u32 asid;
 	int fld = cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64MMFR0_EL1),
 						ID_AA64MMFR0_ASID_SHIFT);

 	switch (fld) {
 	default:
 		pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
 					smp_processor_id(),  fld);
 		fallthrough;
 	case 0:
 		asid = 8;
 		break;
 	case 2:
 		asid = 16;
 	}

 	return asid;
 }

 /* Check if the current cpu's ASIDBits is compatible with asid_bits */
 void verify_cpu_asid_bits(void)
 {
 	u32 asid = get_cpu_asid_bits();

 	if (asid < asid_bits) {
 		/*
 		 * We cannot decrease the ASID size at runtime, so panic if we support
 		 * fewer ASID bits than the boot CPU.
 		 */
 		pr_crit("CPU%d: smaller ASID size(%u) than boot CPU (%u)\n",
 				smp_processor_id(), asid, asid_bits);
 		cpu_panic_kernel();
 	}
 }

 static void set_kpti_asid_bits(unsigned long *map)
 {
 	unsigned int len = BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(unsigned long);
 	/*
 	 * In case of KPTI kernel/user ASIDs are allocated in
 	 * pairs, the bottom bit distinguishes the two: if it
 	 * is set, then the ASID will map only userspace. Thus
 	 * mark even as reserved for kernel.
 	 */
 	memset(map, 0xaa, len);
 }

 static void set_reserved_asid_bits(void)
 {
 	if (pinned_asid_map)
 		bitmap_copy(asid_map, pinned_asid_map, NUM_USER_ASIDS);
 	else if (arm64_kernel_unmapped_at_el0())
 		set_kpti_asid_bits(asid_map);
 	else
 		bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
 }

 #define asid_gen_match(asid) \
 	(!(((asid) ^ atomic64_read(&asid_generation)) >> asid_bits))

 static void flush_context(void)
 {
 	int i;
 	u64 asid;

 	/* Update the list of reserved ASIDs and the ASID bitmap. */
 	set_reserved_asid_bits();

 	for_each_possible_cpu(i) {
 		asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0);
 		/*
 		 * If this CPU has already been through a
 		 * rollover, but hasn't run another task in
 		 * the meantime, we must preserve its reserved
 		 * ASID, as this is the only trace we have of
 		 * the process it is still running.
 		 */
 		if (asid == 0)
 			asid = per_cpu(reserved_asids, i);
 		__set_bit(asid2idx(asid), asid_map);
 		per_cpu(reserved_asids, i) = asid;
 	}

 	/*
 	 * Queue a TLB invalidation for each CPU to perform on next
 	 * context-switch
 	 */
 	cpumask_setall(&tlb_flush_pending);
 }

 static bool check_update_reserved_asid(u64 asid, u64 newasid)
 {
 	int cpu;
 	bool hit = false;

 	/*
 	 * Iterate over the set of reserved ASIDs looking for a match.
 	 * If we find one, then we can update our mm to use newasid
 	 * (i.e. the same ASID in the current generation) but we can't
 	 * exit the loop early, since we need to ensure that all copies
 	 * of the old ASID are updated to reflect the mm. Failure to do
 	 * so could result in us missing the reserved ASID in a future
 	 * generation.
 	 */
 	for_each_possible_cpu(cpu) {
 		if (per_cpu(reserved_asids, cpu) == asid) {
 			hit = true;
 			per_cpu(reserved_asids, cpu) = newasid;
 		}
 	}

 	return hit;
 }

 static u64 new_context(struct mm_struct *mm)
 {
 	static u32 cur_idx = 1;
 	u64 asid = atomic64_read(&mm->context.id);
 	u64 generation = atomic64_read(&asid_generation);

 	if (asid != 0) {
 		u64 newasid = generation | (asid & ~ASID_MASK);

 		/*
 		 * If our current ASID was active during a rollover, we
 		 * can continue to use it and this was just a false alarm.
 		 */
 		if (check_update_reserved_asid(asid, newasid))
 			return newasid;

 		/*
 		 * If it is pinned, we can keep using it. Note that reserved
 		 * takes priority, because even if it is also pinned, we need to
 		 * update the generation into the reserved_asids.
 		 */
 		if (refcount_read(&mm->context.pinned))
 			return newasid;

 		/*
 		 * We had a valid ASID in a previous life, so try to re-use
 		 * it if possible.
 		 */
 		if (!__test_and_set_bit(asid2idx(asid), asid_map))
 			return newasid;
 	}

 	/*
 	 * Allocate a free ASID. If we can't find one, take a note of the
 	 * currently active ASIDs and mark the TLBs as requiring flushes.  We
 	 * always count from ASID #2 (index 1), as we use ASID #0 when setting
 	 * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
 	 * pairs.
 	 */
 	asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
 	if (asid != NUM_USER_ASIDS)
 		goto set_asid;

 	/* We're out of ASIDs, so increment the global generation count */
 	generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION,
 						 &asid_generation);
 	flush_context();

 	/* We have more ASIDs than CPUs, so this will always succeed */
 	asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);

 set_asid:
 	__set_bit(asid, asid_map);
 	cur_idx = asid;
 	return idx2asid(asid) | generation;
 }

 void check_and_switch_context(struct mm_struct *mm)
 {
 	unsigned long flags;
 	unsigned int cpu;
 	u64 asid, old_active_asid;

 	if (system_supports_cnp())
 		cpu_set_reserved_ttbr0();

 	asid = atomic64_read(&mm->context.id);

 	/*
 	 * The memory ordering here is subtle.
 	 * If our active_asids is non-zero and the ASID matches the current
 	 * generation, then we update the active_asids entry with a relaxed
 	 * cmpxchg. Racing with a concurrent rollover means that either:
 	 *
 	 * - We get a zero back from the cmpxchg and end up waiting on the
 	 *   lock. Taking the lock synchronises with the rollover and so
 	 *   we are forced to see the updated generation.
 	 *
 	 * - We get a valid ASID back from the cmpxchg, which means the
 	 *   relaxed xchg in flush_context will treat us as reserved
 	 *   because atomic RmWs are totally ordered for a given location.
 	 */
 	old_active_asid = atomic64_read(this_cpu_ptr(&active_asids));
 	if (old_active_asid && asid_gen_match(asid) &&
 	    atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_asids),
 				     old_active_asid, asid))
 		goto switch_mm_fastpath;

 	raw_spin_lock_irqsave(&cpu_asid_lock, flags);
 	/* Check that our ASID belongs to the current generation. */
 	asid = atomic64_read(&mm->context.id);
 	if (!asid_gen_match(asid)) {
 		asid = new_context(mm);
 		atomic64_set(&mm->context.id, asid);
 	}

 	cpu = smp_processor_id();
 	if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending))
 		local_flush_tlb_all();

 	atomic64_set(this_cpu_ptr(&active_asids), asid);
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

 switch_mm_fastpath:

 	arm64_apply_bp_hardening();

 	/*
 	 * Defer TTBR0_EL1 setting for user threads to uaccess_enable() when
 	 * emulating PAN.
 	 */
 	if (!system_uses_ttbr0_pan())
 		cpu_switch_mm(mm->pgd, mm);
 }

 unsigned long arm64_mm_context_get(struct mm_struct *mm)
 {
 	unsigned long flags;
 	u64 asid;

 	if (!pinned_asid_map)
 		return 0;

 	raw_spin_lock_irqsave(&cpu_asid_lock, flags);

 	asid = atomic64_read(&mm->context.id);

 	if (refcount_inc_not_zero(&mm->context.pinned))
 		goto out_unlock;

 	if (nr_pinned_asids >= max_pinned_asids) {
 		asid = 0;
 		goto out_unlock;
 	}

 	if (!asid_gen_match(asid)) {
 		/*
 		 * We went through one or more rollover since that ASID was
 		 * used. Ensure that it is still valid, or generate a new one.
 		 */
 		asid = new_context(mm);
 		atomic64_set(&mm->context.id, asid);
 	}

 	nr_pinned_asids++;
 	__set_bit(asid2idx(asid), pinned_asid_map);
 	refcount_set(&mm->context.pinned, 1);

 out_unlock:
 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

 	asid &= ~ASID_MASK;

 	/* Set the equivalent of USER_ASID_BIT */
 	if (asid && arm64_kernel_unmapped_at_el0())
 		asid |= 1;

 	return asid;
 }
 EXPORT_SYMBOL_GPL(arm64_mm_context_get);

 void arm64_mm_context_put(struct mm_struct *mm)
 {
 	unsigned long flags;
 	u64 asid = atomic64_read(&mm->context.id);

 	if (!pinned_asid_map)
 		return;

 	raw_spin_lock_irqsave(&cpu_asid_lock, flags);

 	if (refcount_dec_and_test(&mm->context.pinned)) {
 		__clear_bit(asid2idx(asid), pinned_asid_map);
 		nr_pinned_asids--;
 	}

 	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
 }
 EXPORT_SYMBOL_GPL(arm64_mm_context_put);

 /* Errata workaround post TTBRx_EL1 update. */
 asmlinkage void post_ttbr_update_workaround(void)
 {
 	if (!IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456))
 		return;

 	asm(ALTERNATIVE("nop; nop; nop",
 			"ic iallu; dsb nsh; isb",
 			ARM64_WORKAROUND_CAVIUM_27456));
 }

 void cpu_do_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm)
 {
 	unsigned long ttbr1 = read_sysreg(ttbr1_el1);
 	unsigned long asid = ASID(mm);
 	unsigned long ttbr0 = phys_to_ttbr(pgd_phys);

 	/* Skip CNP for the reserved ASID */
 	if (system_supports_cnp() && asid)
 		ttbr0 |= TTBR_CNP_BIT;

 	/* SW PAN needs a copy of the ASID in TTBR0 for entry */
 	if (IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN))
 		ttbr0 |= FIELD_PREP(TTBR_ASID_MASK, asid);

 	/* Set ASID in TTBR1 since TCR.A1 is set */
 	ttbr1 &= ~TTBR_ASID_MASK;
 	ttbr1 |= FIELD_PREP(TTBR_ASID_MASK, asid);

 	write_sysreg(ttbr1, ttbr1_el1);
 	isb();
 	write_sysreg(ttbr0, ttbr0_el1);
 	isb();
 	post_ttbr_update_workaround();
 }

 static int asids_update_limit(void)
 {
 	unsigned long num_available_asids = NUM_USER_ASIDS;

 	if (arm64_kernel_unmapped_at_el0()) {
 		num_available_asids /= 2;
 		if (pinned_asid_map)
 			set_kpti_asid_bits(pinned_asid_map);
 	}
 	/*
 	 * Expect allocation after rollover to fail if we don't have at least
 	 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
 	 */
 	WARN_ON(num_available_asids - 1 <= num_possible_cpus());
 	pr_info("ASID allocator initialised with %lu entries\n",
 		num_available_asids);

 	/*
 	 * There must always be an ASID available after rollover. Ensure that,
 	 * even if all CPUs have a reserved ASID and the maximum number of ASIDs
 	 * are pinned, there still is at least one empty slot in the ASID map.
 	 */
 	max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
 	return 0;
 }
 arch_initcall(asids_update_limit);

 static int asids_init(void)
 {
 	asid_bits = get_cpu_asid_bits();
 	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
 	asid_map = bitmap_zalloc(NUM_USER_ASIDS, GFP_KERNEL);
 	if (!asid_map)
 		panic("Failed to allocate bitmap for %lu ASIDs\n",
 		      NUM_USER_ASIDS);

 	pinned_asid_map = bitmap_zalloc(NUM_USER_ASIDS, GFP_KERNEL);
 	nr_pinned_asids = 0;

 	/*
 	 * We cannot call set_reserved_asid_bits() here because CPU
 	 * caps are not finalized yet, so it is safer to assume KPTI
 	 * and reserve kernel ASID's from beginning.
 	 */
 	if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0))
 		set_kpti_asid_bits(asid_map);
 	return 0;
 }
 early_initcall(asids_init);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Based on arch/arm/mm/context.c
	*
	* Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
	* Copyright (C) 2012 ARM Ltd.
	*/

	#include <linux/bitfield.h>
	#include <linux/bitops.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/mm.h>

	#include <asm/cpufeature.h>
	#include <asm/mmu_context.h>
	#include <asm/smp.h>
	#include <asm/tlbflush.h>

	static u32 asid_bits;
	static DEFINE_RAW_SPINLOCK(cpu_asid_lock);

	static atomic64_t asid_generation;
	static unsigned long *asid_map;

	static DEFINE_PER_CPU(atomic64_t, active_asids);
	static DEFINE_PER_CPU(u64, reserved_asids);
	static cpumask_t tlb_flush_pending;

	static unsigned long max_pinned_asids;
	static unsigned long nr_pinned_asids;
	static unsigned long *pinned_asid_map;

	#define ASID_MASK (~GENMASK(asid_bits - 1, 0))
	#define ASID_FIRST_VERSION (1UL << asid_bits)

	#define NUM_USER_ASIDS ASID_FIRST_VERSION
	#define asid2idx(asid) ((asid) & ~ASID_MASK)
	#define idx2asid(idx) asid2idx(idx)

	/* Get the ASIDBits supported by the current CPU */
	static u32 get_cpu_asid_bits(void)
	{
	u32 asid;
	int fld = cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64MMFR0_EL1),
	ID_AA64MMFR0_ASID_SHIFT);

	switch (fld) {
	default:
	pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
	smp_processor_id(), fld);
	fallthrough;
	case 0:
	asid = 8;
	break;
	case 2:
	asid = 16;
	}

	return asid;
	}

	/* Check if the current cpu's ASIDBits is compatible with asid_bits */
	void verify_cpu_asid_bits(void)
	{
	u32 asid = get_cpu_asid_bits();

	if (asid < asid_bits) {
	/*
	* We cannot decrease the ASID size at runtime, so panic if we support
	* fewer ASID bits than the boot CPU.
	*/
	pr_crit("CPU%d: smaller ASID size(%u) than boot CPU (%u)\n",
	smp_processor_id(), asid, asid_bits);
	cpu_panic_kernel();
	}
	}

	static void set_kpti_asid_bits(unsigned long *map)
	{
	unsigned int len = BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(unsigned long);
	/*
	* In case of KPTI kernel/user ASIDs are allocated in
	* pairs, the bottom bit distinguishes the two: if it
	* is set, then the ASID will map only userspace. Thus
	* mark even as reserved for kernel.
	*/
	memset(map, 0xaa, len);
	}

	static void set_reserved_asid_bits(void)
	{
	if (pinned_asid_map)
	bitmap_copy(asid_map, pinned_asid_map, NUM_USER_ASIDS);
	else if (arm64_kernel_unmapped_at_el0())
	set_kpti_asid_bits(asid_map);
	else
	bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
	}

	#define asid_gen_match(asid) \
	(!(((asid) ^ atomic64_read(&asid_generation)) >> asid_bits))

	static void flush_context(void)
	{
	int i;
	u64 asid;

	/* Update the list of reserved ASIDs and the ASID bitmap. */
	set_reserved_asid_bits();

	for_each_possible_cpu(i) {
	asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0);
	/*
	* If this CPU has already been through a
	* rollover, but hasn't run another task in
	* the meantime, we must preserve its reserved
	* ASID, as this is the only trace we have of
	* the process it is still running.
	*/
	if (asid == 0)
	asid = per_cpu(reserved_asids, i);
	__set_bit(asid2idx(asid), asid_map);
	per_cpu(reserved_asids, i) = asid;
	}

	/*
	* Queue a TLB invalidation for each CPU to perform on next
	* context-switch
	*/
	cpumask_setall(&tlb_flush_pending);
	}

	static bool check_update_reserved_asid(u64 asid, u64 newasid)
	{
	int cpu;
	bool hit = false;

	/*
	* Iterate over the set of reserved ASIDs looking for a match.
	* If we find one, then we can update our mm to use newasid
	* (i.e. the same ASID in the current generation) but we can't
	* exit the loop early, since we need to ensure that all copies
	* of the old ASID are updated to reflect the mm. Failure to do
	* so could result in us missing the reserved ASID in a future
	* generation.
	*/
	for_each_possible_cpu(cpu) {
	if (per_cpu(reserved_asids, cpu) == asid) {
	hit = true;
	per_cpu(reserved_asids, cpu) = newasid;
	}
	}

	return hit;
	}

	static u64 new_context(struct mm_struct *mm)
	{
	static u32 cur_idx = 1;
	u64 asid = atomic64_read(&mm->context.id);
	u64 generation = atomic64_read(&asid_generation);

	if (asid != 0) {
	u64 newasid = generation \| (asid & ~ASID_MASK);

	/*
	* If our current ASID was active during a rollover, we
	* can continue to use it and this was just a false alarm.
	*/
	if (check_update_reserved_asid(asid, newasid))
	return newasid;

	/*
	* If it is pinned, we can keep using it. Note that reserved
	* takes priority, because even if it is also pinned, we need to
	* update the generation into the reserved_asids.
	*/
	if (refcount_read(&mm->context.pinned))
	return newasid;

	/*
	* We had a valid ASID in a previous life, so try to re-use
	* it if possible.
	*/
	if (!__test_and_set_bit(asid2idx(asid), asid_map))
	return newasid;
	}

	/*
	* Allocate a free ASID. If we can't find one, take a note of the
	* currently active ASIDs and mark the TLBs as requiring flushes. We
	* always count from ASID #2 (index 1), as we use ASID #0 when setting
	* a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
	* pairs.
	*/
	asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
	if (asid != NUM_USER_ASIDS)
	goto set_asid;

	/* We're out of ASIDs, so increment the global generation count */
	generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION,
	&asid_generation);
	flush_context();

	/* We have more ASIDs than CPUs, so this will always succeed */
	asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);

	set_asid:
	__set_bit(asid, asid_map);
	cur_idx = asid;
	return idx2asid(asid) \| generation;
	}

	void check_and_switch_context(struct mm_struct *mm)
	{
	unsigned long flags;
	unsigned int cpu;
	u64 asid, old_active_asid;

	if (system_supports_cnp())
	cpu_set_reserved_ttbr0();

	asid = atomic64_read(&mm->context.id);

	/*
	* The memory ordering here is subtle.
	* If our active_asids is non-zero and the ASID matches the current
	* generation, then we update the active_asids entry with a relaxed
	* cmpxchg. Racing with a concurrent rollover means that either:
	*
	* - We get a zero back from the cmpxchg and end up waiting on the
	* lock. Taking the lock synchronises with the rollover and so
	* we are forced to see the updated generation.
	*
	* - We get a valid ASID back from the cmpxchg, which means the
	* relaxed xchg in flush_context will treat us as reserved
	* because atomic RmWs are totally ordered for a given location.
	*/
	old_active_asid = atomic64_read(this_cpu_ptr(&active_asids));
	if (old_active_asid && asid_gen_match(asid) &&
	atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_asids),
	old_active_asid, asid))
	goto switch_mm_fastpath;

	raw_spin_lock_irqsave(&cpu_asid_lock, flags);
	/* Check that our ASID belongs to the current generation. */
	asid = atomic64_read(&mm->context.id);
	if (!asid_gen_match(asid)) {
	asid = new_context(mm);
	atomic64_set(&mm->context.id, asid);
	}

	cpu = smp_processor_id();
	if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending))
	local_flush_tlb_all();

	atomic64_set(this_cpu_ptr(&active_asids), asid);
	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

	switch_mm_fastpath:

	arm64_apply_bp_hardening();

	/*
	* Defer TTBR0_EL1 setting for user threads to uaccess_enable() when
	* emulating PAN.
	*/
	if (!system_uses_ttbr0_pan())
	cpu_switch_mm(mm->pgd, mm);
	}

	unsigned long arm64_mm_context_get(struct mm_struct *mm)
	{
	unsigned long flags;
	u64 asid;

	if (!pinned_asid_map)
	return 0;

	raw_spin_lock_irqsave(&cpu_asid_lock, flags);

	asid = atomic64_read(&mm->context.id);

	if (refcount_inc_not_zero(&mm->context.pinned))
	goto out_unlock;

	if (nr_pinned_asids >= max_pinned_asids) {
	asid = 0;
	goto out_unlock;
	}

	if (!asid_gen_match(asid)) {
	/*
	* We went through one or more rollover since that ASID was
	* used. Ensure that it is still valid, or generate a new one.
	*/
	asid = new_context(mm);
	atomic64_set(&mm->context.id, asid);
	}

	nr_pinned_asids++;
	__set_bit(asid2idx(asid), pinned_asid_map);
	refcount_set(&mm->context.pinned, 1);

	out_unlock:
	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);

	asid &= ~ASID_MASK;

	/* Set the equivalent of USER_ASID_BIT */
	if (asid && arm64_kernel_unmapped_at_el0())
	asid \|= 1;

	return asid;
	}
	EXPORT_SYMBOL_GPL(arm64_mm_context_get);

	void arm64_mm_context_put(struct mm_struct *mm)
	{
	unsigned long flags;
	u64 asid = atomic64_read(&mm->context.id);

	if (!pinned_asid_map)
	return;

	raw_spin_lock_irqsave(&cpu_asid_lock, flags);

	if (refcount_dec_and_test(&mm->context.pinned)) {
	__clear_bit(asid2idx(asid), pinned_asid_map);
	nr_pinned_asids--;
	}

	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
	}
	EXPORT_SYMBOL_GPL(arm64_mm_context_put);

	/* Errata workaround post TTBRx_EL1 update. */
	asmlinkage void post_ttbr_update_workaround(void)
	{
	if (!IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456))
	return;

	asm(ALTERNATIVE("nop; nop; nop",
	"ic iallu; dsb nsh; isb",
	ARM64_WORKAROUND_CAVIUM_27456));
	}

	void cpu_do_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm)
	{
	unsigned long ttbr1 = read_sysreg(ttbr1_el1);
	unsigned long asid = ASID(mm);
	unsigned long ttbr0 = phys_to_ttbr(pgd_phys);

	/* Skip CNP for the reserved ASID */
	if (system_supports_cnp() && asid)
	ttbr0 \|= TTBR_CNP_BIT;

	/* SW PAN needs a copy of the ASID in TTBR0 for entry */
	if (IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN))
	ttbr0 \|= FIELD_PREP(TTBR_ASID_MASK, asid);

	/* Set ASID in TTBR1 since TCR.A1 is set */
	ttbr1 &= ~TTBR_ASID_MASK;
	ttbr1 \|= FIELD_PREP(TTBR_ASID_MASK, asid);

	write_sysreg(ttbr1, ttbr1_el1);
	isb();
	write_sysreg(ttbr0, ttbr0_el1);
	isb();
	post_ttbr_update_workaround();
	}

	static int asids_update_limit(void)
	{
	unsigned long num_available_asids = NUM_USER_ASIDS;

	if (arm64_kernel_unmapped_at_el0()) {
	num_available_asids /= 2;
	if (pinned_asid_map)
	set_kpti_asid_bits(pinned_asid_map);
	}
	/*
	* Expect allocation after rollover to fail if we don't have at least
	* one more ASID than CPUs. ASID #0 is reserved for init_mm.
	*/
	WARN_ON(num_available_asids - 1 <= num_possible_cpus());
	pr_info("ASID allocator initialised with %lu entries\n",
	num_available_asids);

	/*
	* There must always be an ASID available after rollover. Ensure that,
	* even if all CPUs have a reserved ASID and the maximum number of ASIDs
	* are pinned, there still is at least one empty slot in the ASID map.
	*/
	max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
	return 0;
	}
	arch_initcall(asids_update_limit);

	static int asids_init(void)
	{
	asid_bits = get_cpu_asid_bits();
	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
	asid_map = bitmap_zalloc(NUM_USER_ASIDS, GFP_KERNEL);
	if (!asid_map)
	panic("Failed to allocate bitmap for %lu ASIDs\n",
	NUM_USER_ASIDS);

	pinned_asid_map = bitmap_zalloc(NUM_USER_ASIDS, GFP_KERNEL);
	nr_pinned_asids = 0;

	/*
	* We cannot call set_reserved_asid_bits() here because CPU
	* caps are not finalized yet, so it is safer to assume KPTI
	* and reserve kernel ASID's from beginning.
	*/
	if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0))
	set_kpti_asid_bits(asid_map);
	return 0;
	}
	early_initcall(asids_init);