1 files changed, 291 insertions, 0 deletions
diff --git a/arch/mips/mm/context.c b/arch/mips/mm/context.c
new file mode 100644
index 000000000..b25564090
--- /dev/null
+++ b/arch/mips/mm/context.c
@@ -0,0 +1,291 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/atomic.h>
+#include <linux/mmu_context.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+
+static DEFINE_RAW_SPINLOCK(cpu_mmid_lock);
+
+static atomic64_t mmid_version;
+static unsigned int num_mmids;
+static unsigned long *mmid_map;
+
+static DEFINE_PER_CPU(u64, reserved_mmids);
+static cpumask_t tlb_flush_pending;
+
+static bool asid_versions_eq(int cpu, u64 a, u64 b)
+{
+	return ((a ^ b) & asid_version_mask(cpu)) == 0;
+}
+
+void get_new_mmu_context(struct mm_struct *mm)
+{
+	unsigned int cpu;
+	u64 asid;
+
+	/*
+	 * This function is specific to ASIDs, and should not be called when
+	 * MMIDs are in use.
+	 */
+	if (WARN_ON(IS_ENABLED(CONFIG_DEBUG_VM) && cpu_has_mmid))
+		return;
+
+	cpu = smp_processor_id();
+	asid = asid_cache(cpu);
+
+	if (!((asid += cpu_asid_inc()) & cpu_asid_mask(&cpu_data[cpu]))) {
+		if (cpu_has_vtag_icache)
+			flush_icache_all();
+		local_flush_tlb_all();	/* start new asid cycle */
+	}
+
+	set_cpu_context(cpu, mm, asid);
+	asid_cache(cpu) = asid;
+}
+EXPORT_SYMBOL_GPL(get_new_mmu_context);
+
+void check_mmu_context(struct mm_struct *mm)
+{
+	unsigned int cpu = smp_processor_id();
+
+	/*
+	 * This function is specific to ASIDs, and should not be called when
+	 * MMIDs are in use.
+	 */
+	if (WARN_ON(IS_ENABLED(CONFIG_DEBUG_VM) && cpu_has_mmid))
+		return;
+
+	/* Check if our ASID is of an older version and thus invalid */
+	if (!asid_versions_eq(cpu, cpu_context(cpu, mm), asid_cache(cpu)))
+		get_new_mmu_context(mm);
+}
+EXPORT_SYMBOL_GPL(check_mmu_context);
+
+static void flush_context(void)
+{
+	u64 mmid;
+	int cpu;
+
+	/* Update the list of reserved MMIDs and the MMID bitmap */
+	bitmap_clear(mmid_map, 0, num_mmids);
+
+	/* Reserve an MMID for kmap/wired entries */
+	__set_bit(MMID_KERNEL_WIRED, mmid_map);
+
+	for_each_possible_cpu(cpu) {
+		mmid = xchg_relaxed(&cpu_data[cpu].asid_cache, 0);
+
+		/*
+		 * If this CPU has already been through a
+		 * rollover, but hasn't run another task in
+		 * the meantime, we must preserve its reserved
+		 * MMID, as this is the only trace we have of
+		 * the process it is still running.
+		 */
+		if (mmid == 0)
+			mmid = per_cpu(reserved_mmids, cpu);
+
+		__set_bit(mmid & cpu_asid_mask(&cpu_data[cpu]), mmid_map);
+		per_cpu(reserved_mmids, cpu) = mmid;
+	}
+
+	/*
+	 * Queue a TLB invalidation for each CPU to perform on next
+	 * context-switch
+	 */
+	cpumask_setall(&tlb_flush_pending);
+}
+
+static bool check_update_reserved_mmid(u64 mmid, u64 newmmid)
+{
+	bool hit;
+	int cpu;
+
+	/*
+	 * Iterate over the set of reserved MMIDs looking for a match.
+	 * If we find one, then we can update our mm to use newmmid
+	 * (i.e. the same MMID in the current generation) but we can't
+	 * exit the loop early, since we need to ensure that all copies
+	 * of the old MMID are updated to reflect the mm. Failure to do
+	 * so could result in us missing the reserved MMID in a future
+	 * generation.
+	 */
+	hit = false;
+	for_each_possible_cpu(cpu) {
+		if (per_cpu(reserved_mmids, cpu) == mmid) {
+			hit = true;
+			per_cpu(reserved_mmids, cpu) = newmmid;
+		}
+	}
+
+	return hit;
+}
+
+static u64 get_new_mmid(struct mm_struct *mm)
+{
+	static u32 cur_idx = MMID_KERNEL_WIRED + 1;
+	u64 mmid, version, mmid_mask;
+
+	mmid = cpu_context(0, mm);
+	version = atomic64_read(&mmid_version);
+	mmid_mask = cpu_asid_mask(&boot_cpu_data);
+
+	if (!asid_versions_eq(0, mmid, 0)) {
+		u64 newmmid = version | (mmid & mmid_mask);
+
+		/*
+		 * If our current MMID was active during a rollover, we
+		 * can continue to use it and this was just a false alarm.
+		 */
+		if (check_update_reserved_mmid(mmid, newmmid)) {
+			mmid = newmmid;
+			goto set_context;
+		}
+
+		/*
+		 * We had a valid MMID in a previous life, so try to re-use
+		 * it if possible.
+		 */
+		if (!__test_and_set_bit(mmid & mmid_mask, mmid_map)) {
+			mmid = newmmid;
+			goto set_context;
+		}
+	}
+
+	/* Allocate a free MMID */
+	mmid = find_next_zero_bit(mmid_map, num_mmids, cur_idx);
+	if (mmid != num_mmids)
+		goto reserve_mmid;
+
+	/* We're out of MMIDs, so increment the global version */
+	version = atomic64_add_return_relaxed(asid_first_version(0),
+					      &mmid_version);
+
+	/* Note currently active MMIDs & mark TLBs as requiring flushes */
+	flush_context();
+
+	/* We have more MMIDs than CPUs, so this will always succeed */
+	mmid = find_first_zero_bit(mmid_map, num_mmids);
+
+reserve_mmid:
+	__set_bit(mmid, mmid_map);
+	cur_idx = mmid;
+	mmid |= version;
+set_context:
+	set_cpu_context(0, mm, mmid);
+	return mmid;
+}
+
+void check_switch_mmu_context(struct mm_struct *mm)
+{
+	unsigned int cpu = smp_processor_id();
+	u64 ctx, old_active_mmid;
+	unsigned long flags;
+
+	if (!cpu_has_mmid) {
+		check_mmu_context(mm);
+		write_c0_entryhi(cpu_asid(cpu, mm));
+		goto setup_pgd;
+	}
+
+	/*
+	 * MMID switch fast-path, to avoid acquiring cpu_mmid_lock when it's
+	 * unnecessary.
+	 *
+	 * The memory ordering here is subtle. If our active_mmids is non-zero
+	 * and the MMID matches the current version, then we update the CPU's
+	 * asid_cache 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
+	 *   cpu_mmid_lock in check_mmu_context(). Taking the lock synchronises
+	 *   with the rollover and so we are forced to see the updated
+	 *   generation.
+	 *
+	 * - We get a valid MMID 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.
+	 */
+	ctx = cpu_context(cpu, mm);
+	old_active_mmid = READ_ONCE(cpu_data[cpu].asid_cache);
+	if (!old_active_mmid ||
+	    !asid_versions_eq(cpu, ctx, atomic64_read(&mmid_version)) ||
+	    !cmpxchg_relaxed(&cpu_data[cpu].asid_cache, old_active_mmid, ctx)) {
+		raw_spin_lock_irqsave(&cpu_mmid_lock, flags);
+
+		ctx = cpu_context(cpu, mm);
+		if (!asid_versions_eq(cpu, ctx, atomic64_read(&mmid_version)))
+			ctx = get_new_mmid(mm);
+
+		WRITE_ONCE(cpu_data[cpu].asid_cache, ctx);
+		raw_spin_unlock_irqrestore(&cpu_mmid_lock, flags);
+	}
+
+	/*
+	 * Invalidate the local TLB if needed. Note that we must only clear our
+	 * bit in tlb_flush_pending after this is complete, so that the
+	 * cpu_has_shared_ftlb_entries case below isn't misled.
+	 */
+	if (cpumask_test_cpu(cpu, &tlb_flush_pending)) {
+		if (cpu_has_vtag_icache)
+			flush_icache_all();
+		local_flush_tlb_all();
+		cpumask_clear_cpu(cpu, &tlb_flush_pending);
+	}
+
+	write_c0_memorymapid(ctx & cpu_asid_mask(&boot_cpu_data));
+
+	/*
+	 * If this CPU shares FTLB entries with its siblings and one or more of
+	 * those siblings hasn't yet invalidated its TLB following a version
+	 * increase then we need to invalidate any TLB entries for our MMID
+	 * that we might otherwise pick up from a sibling.
+	 *
+	 * We ifdef on CONFIG_SMP because cpu_sibling_map isn't defined in
+	 * CONFIG_SMP=n kernels.
+	 */
+#ifdef CONFIG_SMP
+	if (cpu_has_shared_ftlb_entries &&
+	    cpumask_intersects(&tlb_flush_pending, &cpu_sibling_map[cpu])) {
+		/* Ensure we operate on the new MMID */
+		mtc0_tlbw_hazard();
+
+		/*
+		 * Invalidate all TLB entries associated with the new
+		 * MMID, and wait for the invalidation to complete.
+		 */
+		ginvt_mmid();
+		sync_ginv();
+	}
+#endif
+
+setup_pgd:
+	TLBMISS_HANDLER_SETUP_PGD(mm->pgd);
+}
+EXPORT_SYMBOL_GPL(check_switch_mmu_context);
+
+static int mmid_init(void)
+{
+	if (!cpu_has_mmid)
+		return 0;
+
+	/*
+	 * Expect allocation after rollover to fail if we don't have at least
+	 * one more MMID than CPUs.
+	 */
+	num_mmids = asid_first_version(0);
+	WARN_ON(num_mmids <= num_possible_cpus());
+
+	atomic64_set(&mmid_version, asid_first_version(0));
+	mmid_map = kcalloc(BITS_TO_LONGS(num_mmids), sizeof(*mmid_map),
+			   GFP_KERNEL);
+	if (!mmid_map)
+		panic("Failed to allocate bitmap for %u MMIDs\n", num_mmids);
+
+	/* Reserve an MMID for kmap/wired entries */
+	__set_bit(MMID_KERNEL_WIRED, mmid_map);
+
+	pr_info("MMID allocator initialised with %u entries\n", num_mmids);
+	return 0;
+}
+early_initcall(mmid_init);