1 files changed, 422 insertions, 0 deletions
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
new file mode 100644
index 000000000..e1e0dca01
--- /dev/null
+++ b/arch/arm64/mm/context.c
@@ -0,0 +1,422 @@
+// 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 ctxid2asid(asid)	((asid) & ~ASID_MASK)
+#define asid2ctxid(asid, genid)	((asid) | (genid))
+
+/* 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_EL1_ASIDBITS_SHIFT);
+
+	switch (fld) {
+	default:
+		pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
+					smp_processor_id(),  fld);
+		fallthrough;
+	case ID_AA64MMFR0_EL1_ASIDBITS_8:
+		asid = 8;
+		break;
+	case ID_AA64MMFR0_EL1_ASIDBITS_16:
+		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(ctxid2asid(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 = asid2ctxid(ctxid2asid(asid), generation);
+
+		/*
+		 * 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(ctxid2asid(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 asid2ctxid(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(ctxid2asid(asid), pinned_asid_map);
+	refcount_set(&mm->context.pinned, 1);
+
+out_unlock:
+	raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
+
+	asid = ctxid2asid(asid);
+
+	/* 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(ctxid2asid(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);