1 files changed, 425 insertions, 0 deletions
diff --git a/arch/powerpc/mm/nohash/mmu_context.c b/arch/powerpc/mm/nohash/mmu_context.c
new file mode 100644
index 000000000..ccd5819b1
--- /dev/null
+++ b/arch/powerpc/mm/nohash/mmu_context.c
@@ -0,0 +1,425 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * This file contains the routines for handling the MMU on those
+ * PowerPC implementations where the MMU is not using the hash
+ * table, such as 8xx, 4xx, BookE's etc...
+ *
+ * Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org>
+ *                IBM Corp.
+ *
+ *  Derived from previous arch/powerpc/mm/mmu_context.c
+ *  and arch/powerpc/include/asm/mmu_context.h
+ *
+ * TODO:
+ *
+ *   - The global context lock will not scale very well
+ *   - The maps should be dynamically allocated to allow for processors
+ *     that support more PID bits at runtime
+ *   - Implement flush_tlb_mm() by making the context stale and picking
+ *     a new one
+ *   - More aggressively clear stale map bits and maybe find some way to
+ *     also clear mm->cpu_vm_mask bits when processes are migrated
+ */
+
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/memblock.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/slab.h>
+
+#include <asm/mmu_context.h>
+#include <asm/tlbflush.h>
+#include <asm/smp.h>
+#include <asm/kup.h>
+
+#include <mm/mmu_decl.h>
+
+/*
+ * Room for two PTE table pointers, usually the kernel and current user
+ * pointer to their respective root page table (pgdir).
+ */
+void *abatron_pteptrs[2];
+
+/*
+ * The MPC8xx has only 16 contexts. We rotate through them on each task switch.
+ * A better way would be to keep track of tasks that own contexts, and implement
+ * an LRU usage. That way very active tasks don't always have to pay the TLB
+ * reload overhead. The kernel pages are mapped shared, so the kernel can run on
+ * behalf of any task that makes a kernel entry. Shared does not mean they are
+ * not protected, just that the ASID comparison is not performed. -- Dan
+ *
+ * The IBM4xx has 256 contexts, so we can just rotate through these as a way of
+ * "switching" contexts. If the TID of the TLB is zero, the PID/TID comparison
+ * is disabled, so we can use a TID of zero to represent all kernel pages as
+ * shared among all contexts. -- Dan
+ *
+ * The IBM 47x core supports 16-bit PIDs, thus 65535 contexts. We should
+ * normally never have to steal though the facility is present if needed.
+ * -- BenH
+ */
+#define FIRST_CONTEXT 1
+#if defined(CONFIG_PPC_8xx)
+#define LAST_CONTEXT 16
+#elif defined(CONFIG_PPC_47x)
+#define LAST_CONTEXT 65535
+#else
+#define LAST_CONTEXT 255
+#endif
+
+static unsigned int next_context, nr_free_contexts;
+static unsigned long *context_map;
+static unsigned long *stale_map[NR_CPUS];
+static struct mm_struct **context_mm;
+static DEFINE_RAW_SPINLOCK(context_lock);
+
+#define CTX_MAP_SIZE	\
+	(sizeof(unsigned long) * (LAST_CONTEXT / BITS_PER_LONG + 1))
+
+
+/* Steal a context from a task that has one at the moment.
+ *
+ * This is used when we are running out of available PID numbers
+ * on the processors.
+ *
+ * This isn't an LRU system, it just frees up each context in
+ * turn (sort-of pseudo-random replacement :).  This would be the
+ * place to implement an LRU scheme if anyone was motivated to do it.
+ *  -- paulus
+ *
+ * For context stealing, we use a slightly different approach for
+ * SMP and UP. Basically, the UP one is simpler and doesn't use
+ * the stale map as we can just flush the local CPU
+ *  -- benh
+ */
+static unsigned int steal_context_smp(unsigned int id)
+{
+	struct mm_struct *mm;
+	unsigned int cpu, max, i;
+
+	max = LAST_CONTEXT - FIRST_CONTEXT;
+
+	/* Attempt to free next_context first and then loop until we manage */
+	while (max--) {
+		/* Pick up the victim mm */
+		mm = context_mm[id];
+
+		/* We have a candidate victim, check if it's active, on SMP
+		 * we cannot steal active contexts
+		 */
+		if (mm->context.active) {
+			id++;
+			if (id > LAST_CONTEXT)
+				id = FIRST_CONTEXT;
+			continue;
+		}
+
+		/* Mark this mm has having no context anymore */
+		mm->context.id = MMU_NO_CONTEXT;
+
+		/* Mark it stale on all CPUs that used this mm. For threaded
+		 * implementations, we set it on all threads on each core
+		 * represented in the mask. A future implementation will use
+		 * a core map instead but this will do for now.
+		 */
+		for_each_cpu(cpu, mm_cpumask(mm)) {
+			for (i = cpu_first_thread_sibling(cpu);
+			     i <= cpu_last_thread_sibling(cpu); i++) {
+				if (stale_map[i])
+					__set_bit(id, stale_map[i]);
+			}
+			cpu = i - 1;
+		}
+		return id;
+	}
+
+	/* This will happen if you have more CPUs than available contexts,
+	 * all we can do here is wait a bit and try again
+	 */
+	raw_spin_unlock(&context_lock);
+	cpu_relax();
+	raw_spin_lock(&context_lock);
+
+	/* This will cause the caller to try again */
+	return MMU_NO_CONTEXT;
+}
+
+static unsigned int steal_all_contexts(void)
+{
+	struct mm_struct *mm;
+	int cpu = smp_processor_id();
+	unsigned int id;
+
+	for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) {
+		/* Pick up the victim mm */
+		mm = context_mm[id];
+
+		/* Mark this mm as having no context anymore */
+		mm->context.id = MMU_NO_CONTEXT;
+		if (id != FIRST_CONTEXT) {
+			context_mm[id] = NULL;
+			__clear_bit(id, context_map);
+		}
+		if (IS_ENABLED(CONFIG_SMP))
+			__clear_bit(id, stale_map[cpu]);
+	}
+
+	/* Flush the TLB for all contexts (not to be used on SMP) */
+	_tlbil_all();
+
+	nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT;
+
+	return FIRST_CONTEXT;
+}
+
+/* Note that this will also be called on SMP if all other CPUs are
+ * offlined, which means that it may be called for cpu != 0. For
+ * this to work, we somewhat assume that CPUs that are onlined
+ * come up with a fully clean TLB (or are cleaned when offlined)
+ */
+static unsigned int steal_context_up(unsigned int id)
+{
+	struct mm_struct *mm;
+	int cpu = smp_processor_id();
+
+	/* Pick up the victim mm */
+	mm = context_mm[id];
+
+	/* Flush the TLB for that context */
+	local_flush_tlb_mm(mm);
+
+	/* Mark this mm has having no context anymore */
+	mm->context.id = MMU_NO_CONTEXT;
+
+	/* XXX This clear should ultimately be part of local_flush_tlb_mm */
+	if (IS_ENABLED(CONFIG_SMP))
+		__clear_bit(id, stale_map[cpu]);
+
+	return id;
+}
+
+static void set_context(unsigned long id, pgd_t *pgd)
+{
+	if (IS_ENABLED(CONFIG_PPC_8xx)) {
+		s16 offset = (s16)(__pa(swapper_pg_dir));
+
+		/*
+		 * Register M_TWB will contain base address of level 1 table minus the
+		 * lower part of the kernel PGDIR base address, so that all accesses to
+		 * level 1 table are done relative to lower part of kernel PGDIR base
+		 * address.
+		 */
+		mtspr(SPRN_M_TWB, __pa(pgd) - offset);
+
+		/* Update context */
+		mtspr(SPRN_M_CASID, id - 1);
+
+		/* sync */
+		mb();
+	} else if (kuap_is_disabled()) {
+		if (IS_ENABLED(CONFIG_40x))
+			mb();	/* sync */
+
+		mtspr(SPRN_PID, id);
+		isync();
+	}
+}
+
+void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
+			struct task_struct *tsk)
+{
+	unsigned int id;
+	unsigned int i, cpu = smp_processor_id();
+	unsigned long *map;
+
+	/* No lockless fast path .. yet */
+	raw_spin_lock(&context_lock);
+
+	if (IS_ENABLED(CONFIG_SMP)) {
+		/* Mark us active and the previous one not anymore */
+		next->context.active++;
+		if (prev) {
+			WARN_ON(prev->context.active < 1);
+			prev->context.active--;
+		}
+	}
+
+ again:
+
+	/* If we already have a valid assigned context, skip all that */
+	id = next->context.id;
+	if (likely(id != MMU_NO_CONTEXT))
+		goto ctxt_ok;
+
+	/* We really don't have a context, let's try to acquire one */
+	id = next_context;
+	if (id > LAST_CONTEXT)
+		id = FIRST_CONTEXT;
+	map = context_map;
+
+	/* No more free contexts, let's try to steal one */
+	if (nr_free_contexts == 0) {
+		if (num_online_cpus() > 1) {
+			id = steal_context_smp(id);
+			if (id == MMU_NO_CONTEXT)
+				goto again;
+			goto stolen;
+		}
+		if (IS_ENABLED(CONFIG_PPC_8xx))
+			id = steal_all_contexts();
+		else
+			id = steal_context_up(id);
+		goto stolen;
+	}
+	nr_free_contexts--;
+
+	/* We know there's at least one free context, try to find it */
+	while (__test_and_set_bit(id, map)) {
+		id = find_next_zero_bit(map, LAST_CONTEXT+1, id);
+		if (id > LAST_CONTEXT)
+			id = FIRST_CONTEXT;
+	}
+ stolen:
+	next_context = id + 1;
+	context_mm[id] = next;
+	next->context.id = id;
+
+ ctxt_ok:
+
+	/* If that context got marked stale on this CPU, then flush the
+	 * local TLB for it and unmark it before we use it
+	 */
+	if (IS_ENABLED(CONFIG_SMP) && test_bit(id, stale_map[cpu])) {
+		local_flush_tlb_mm(next);
+
+		/* XXX This clear should ultimately be part of local_flush_tlb_mm */
+		for (i = cpu_first_thread_sibling(cpu);
+		     i <= cpu_last_thread_sibling(cpu); i++) {
+			if (stale_map[i])
+				__clear_bit(id, stale_map[i]);
+		}
+	}
+
+	/* Flick the MMU and release lock */
+	if (IS_ENABLED(CONFIG_BDI_SWITCH))
+		abatron_pteptrs[1] = next->pgd;
+	set_context(id, next->pgd);
+#if defined(CONFIG_BOOKE_OR_40x) && defined(CONFIG_PPC_KUAP)
+	tsk->thread.pid = id;
+#endif
+	raw_spin_unlock(&context_lock);
+}
+
+/*
+ * Set up the context for a new address space.
+ */
+int init_new_context(struct task_struct *t, struct mm_struct *mm)
+{
+	mm->context.id = MMU_NO_CONTEXT;
+	mm->context.active = 0;
+	pte_frag_set(&mm->context, NULL);
+	return 0;
+}
+
+/*
+ * We're finished using the context for an address space.
+ */
+void destroy_context(struct mm_struct *mm)
+{
+	unsigned long flags;
+	unsigned int id;
+
+	if (mm->context.id == MMU_NO_CONTEXT)
+		return;
+
+	WARN_ON(mm->context.active != 0);
+
+	raw_spin_lock_irqsave(&context_lock, flags);
+	id = mm->context.id;
+	if (id != MMU_NO_CONTEXT) {
+		__clear_bit(id, context_map);
+		mm->context.id = MMU_NO_CONTEXT;
+		context_mm[id] = NULL;
+		nr_free_contexts++;
+	}
+	raw_spin_unlock_irqrestore(&context_lock, flags);
+}
+
+static int mmu_ctx_cpu_prepare(unsigned int cpu)
+{
+	/* We don't touch CPU 0 map, it's allocated at aboot and kept
+	 * around forever
+	 */
+	if (cpu == boot_cpuid)
+		return 0;
+
+	stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL);
+	return 0;
+}
+
+static int mmu_ctx_cpu_dead(unsigned int cpu)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+	if (cpu == boot_cpuid)
+		return 0;
+
+	kfree(stale_map[cpu]);
+	stale_map[cpu] = NULL;
+
+	/* We also clear the cpu_vm_mask bits of CPUs going away */
+	clear_tasks_mm_cpumask(cpu);
+#endif
+	return 0;
+}
+
+/*
+ * Initialize the context management stuff.
+ */
+void __init mmu_context_init(void)
+{
+	/* Mark init_mm as being active on all possible CPUs since
+	 * we'll get called with prev == init_mm the first time
+	 * we schedule on a given CPU
+	 */
+	init_mm.context.active = NR_CPUS;
+
+	/*
+	 * Allocate the maps used by context management
+	 */
+	context_map = memblock_alloc(CTX_MAP_SIZE, SMP_CACHE_BYTES);
+	if (!context_map)
+		panic("%s: Failed to allocate %zu bytes\n", __func__,
+		      CTX_MAP_SIZE);
+	context_mm = memblock_alloc(sizeof(void *) * (LAST_CONTEXT + 1),
+				    SMP_CACHE_BYTES);
+	if (!context_mm)
+		panic("%s: Failed to allocate %zu bytes\n", __func__,
+		      sizeof(void *) * (LAST_CONTEXT + 1));
+	if (IS_ENABLED(CONFIG_SMP)) {
+		stale_map[boot_cpuid] = memblock_alloc(CTX_MAP_SIZE, SMP_CACHE_BYTES);
+		if (!stale_map[boot_cpuid])
+			panic("%s: Failed to allocate %zu bytes\n", __func__,
+			      CTX_MAP_SIZE);
+
+		cpuhp_setup_state_nocalls(CPUHP_POWERPC_MMU_CTX_PREPARE,
+					  "powerpc/mmu/ctx:prepare",
+					  mmu_ctx_cpu_prepare, mmu_ctx_cpu_dead);
+	}
+
+	printk(KERN_INFO
+	       "MMU: Allocated %zu bytes of context maps for %d contexts\n",
+	       2 * CTX_MAP_SIZE + (sizeof(void *) * (LAST_CONTEXT + 1)),
+	       LAST_CONTEXT - FIRST_CONTEXT + 1);
+
+	/*
+	 * Some processors have too few contexts to reserve one for
+	 * init_mm, and require using context 0 for a normal task.
+	 * Other processors reserve the use of context zero for the kernel.
+	 * This code assumes FIRST_CONTEXT < 32.
+	 */
+	context_map[0] = (1 << FIRST_CONTEXT) - 1;
+	next_context = FIRST_CONTEXT;
+	nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT + 1;
+}