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

 /*
  * Based on arch/arm/mm/context.c
  *
  * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
  * Copyright (C) 2012 ARM Ltd.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #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;

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

 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 #define NUM_USER_ASIDS		(ASID_FIRST_VERSION >> 1)
 #define asid2idx(asid)		(((asid) & ~ASID_MASK) >> 1)
 #define idx2asid(idx)		(((idx) << 1) & ~ASID_MASK)
 #else
 #define NUM_USER_ASIDS		(ASID_FIRST_VERSION)
 #define asid2idx(asid)		((asid) & ~ASID_MASK)
 #define idx2asid(idx)		asid2idx(idx)
 #endif

 /* 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 flush_context(unsigned int cpu)
 {
 	int i;
 	u64 asid;

 	/* Update the list of reserved ASIDs and the ASID bitmap. */
 	bitmap_clear(asid_map, 0, NUM_USER_ASIDS);

 	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, unsigned int cpu)
 {
 	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;

 		/*
 		 * 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(cpu);

 	/* 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 int cpu)
 {
 	unsigned long flags;
 	u64 asid, old_active_asid;

 	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(&per_cpu(active_asids, cpu));
 	if (old_active_asid &&
 	    !((asid ^ atomic64_read(&asid_generation)) >> asid_bits) &&
 	    atomic64_cmpxchg_relaxed(&per_cpu(active_asids, cpu),
 				     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 ^ atomic64_read(&asid_generation)) >> asid_bits) {
 		asid = new_context(mm, cpu);
 		atomic64_set(&mm->context.id, asid);
 	}

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

 	atomic64_set(&per_cpu(active_asids, cpu), 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);
 }

 /* Errata workaround post TTBRx_EL1 update. */
 asmlinkage void post_ttbr_update_workaround(void)
 {
 	asm(ALTERNATIVE("nop; nop; nop",
 			"ic iallu; dsb nsh; isb",
 			ARM64_WORKAROUND_CAVIUM_27456,
 			CONFIG_CAVIUM_ERRATUM_27456));
 }

 static int asids_init(void)
 {
 	asid_bits = get_cpu_asid_bits();
 	/*
 	 * 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_USER_ASIDS - 1 <= num_possible_cpus());
 	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
 	asid_map = kzalloc(BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(*asid_map),
 			   GFP_KERNEL);
 	if (!asid_map)
 		panic("Failed to allocate bitmap for %lu ASIDs\n",
 		      NUM_USER_ASIDS);

 	pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS);
 	return 0;
 }
 early_initcall(asids_init);
	/*
	* Based on arch/arm/mm/context.c
	*
	* Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
	* Copyright (C) 2012 ARM Ltd.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#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;

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

	#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
	#define NUM_USER_ASIDS (ASID_FIRST_VERSION >> 1)
	#define asid2idx(asid) (((asid) & ~ASID_MASK) >> 1)
	#define idx2asid(idx) (((idx) << 1) & ~ASID_MASK)
	#else
	#define NUM_USER_ASIDS (ASID_FIRST_VERSION)
	#define asid2idx(asid) ((asid) & ~ASID_MASK)
	#define idx2asid(idx) asid2idx(idx)
	#endif

	/* 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 flush_context(unsigned int cpu)
	{
	int i;
	u64 asid;

	/* Update the list of reserved ASIDs and the ASID bitmap. */
	bitmap_clear(asid_map, 0, NUM_USER_ASIDS);

	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, unsigned int cpu)
	{
	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;

	/*
	* 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(cpu);

	/* 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 int cpu)
	{
	unsigned long flags;
	u64 asid, old_active_asid;

	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(&per_cpu(active_asids, cpu));
	if (old_active_asid &&
	!((asid ^ atomic64_read(&asid_generation)) >> asid_bits) &&
	atomic64_cmpxchg_relaxed(&per_cpu(active_asids, cpu),
	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 ^ atomic64_read(&asid_generation)) >> asid_bits) {
	asid = new_context(mm, cpu);
	atomic64_set(&mm->context.id, asid);
	}

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

	atomic64_set(&per_cpu(active_asids, cpu), 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);
	}

	/* Errata workaround post TTBRx_EL1 update. */
	asmlinkage void post_ttbr_update_workaround(void)
	{
	asm(ALTERNATIVE("nop; nop; nop",
	"ic iallu; dsb nsh; isb",
	ARM64_WORKAROUND_CAVIUM_27456,
	CONFIG_CAVIUM_ERRATUM_27456));
	}

	static int asids_init(void)
	{
	asid_bits = get_cpu_asid_bits();
	/*
	* 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_USER_ASIDS - 1 <= num_possible_cpus());
	atomic64_set(&asid_generation, ASID_FIRST_VERSION);
	asid_map = kzalloc(BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(*asid_map),
	GFP_KERNEL);
	if (!asid_map)
	panic("Failed to allocate bitmap for %lu ASIDs\n",
	NUM_USER_ASIDS);

	pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS);
	return 0;
	}
	early_initcall(asids_init);