| // 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 |
| */ |
| |
| //#define DEBUG_MAP_CONSISTENCY |
| //#define DEBUG_CLAMP_LAST_CONTEXT 31 |
| //#define DEBUG_HARDER |
| |
| /* We don't use DEBUG because it tends to be compiled in always nowadays |
| * and this would generate way too much output |
| */ |
| #ifdef DEBUG_HARDER |
| #define pr_hard(args...) printk(KERN_DEBUG args) |
| #define pr_hardcont(args...) printk(KERN_CONT args) |
| #else |
| #define pr_hard(args...) do { } while(0) |
| #define pr_hardcont(args...) do { } while(0) |
| #endif |
| |
| #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 <mm/mmu_decl.h> |
| |
| /* |
| * 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 |
| #ifdef DEBUG_CLAMP_LAST_CONTEXT |
| #define LAST_CONTEXT DEBUG_CLAMP_LAST_CONTEXT |
| #elif 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; |
| #ifdef CONFIG_SMP |
| static unsigned long *stale_map[NR_CPUS]; |
| #endif |
| 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 |
| */ |
| #ifdef CONFIG_SMP |
| 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; |
| } |
| pr_hardcont(" | steal %d from 0x%p", id, mm); |
| |
| /* 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; |
| } |
| #endif /* CONFIG_SMP */ |
| |
| static unsigned int steal_all_contexts(void) |
| { |
| struct mm_struct *mm; |
| #ifdef CONFIG_SMP |
| int cpu = smp_processor_id(); |
| #endif |
| unsigned int id; |
| |
| for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) { |
| /* Pick up the victim mm */ |
| mm = context_mm[id]; |
| |
| pr_hardcont(" | steal %d from 0x%p", id, mm); |
| |
| /* 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); |
| #ifdef DEBUG_MAP_CONSISTENCY |
| mm->context.active = 0; |
| #endif |
| } |
| #ifdef CONFIG_SMP |
| __clear_bit(id, stale_map[cpu]); |
| #endif |
| } |
| |
| /* 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; |
| #ifdef CONFIG_SMP |
| int cpu = smp_processor_id(); |
| #endif |
| |
| /* Pick up the victim mm */ |
| mm = context_mm[id]; |
| |
| pr_hardcont(" | steal %d from 0x%p", id, mm); |
| |
| /* 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 */ |
| #ifdef CONFIG_SMP |
| __clear_bit(id, stale_map[cpu]); |
| #endif |
| |
| return id; |
| } |
| |
| #ifdef DEBUG_MAP_CONSISTENCY |
| static void context_check_map(void) |
| { |
| unsigned int id, nrf, nact; |
| |
| nrf = nact = 0; |
| for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) { |
| int used = test_bit(id, context_map); |
| if (!used) |
| nrf++; |
| if (used != (context_mm[id] != NULL)) |
| pr_err("MMU: Context %d is %s and MM is %p !\n", |
| id, used ? "used" : "free", context_mm[id]); |
| if (context_mm[id] != NULL) |
| nact += context_mm[id]->context.active; |
| } |
| if (nrf != nr_free_contexts) { |
| pr_err("MMU: Free context count out of sync ! (%d vs %d)\n", |
| nr_free_contexts, nrf); |
| nr_free_contexts = nrf; |
| } |
| if (nact > num_online_cpus()) |
| pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n", |
| nact, num_online_cpus()); |
| if (FIRST_CONTEXT > 0 && !test_bit(0, context_map)) |
| pr_err("MMU: Context 0 has been freed !!!\n"); |
| } |
| #else |
| static void context_check_map(void) { } |
| #endif |
| |
| void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, |
| struct task_struct *tsk) |
| { |
| unsigned int id; |
| #ifdef CONFIG_SMP |
| unsigned int i, cpu = smp_processor_id(); |
| #endif |
| unsigned long *map; |
| |
| /* No lockless fast path .. yet */ |
| raw_spin_lock(&context_lock); |
| |
| pr_hard("[%d] activating context for mm @%p, active=%d, id=%d", |
| cpu, next, next->context.active, next->context.id); |
| |
| #ifdef CONFIG_SMP |
| /* Mark us active and the previous one not anymore */ |
| next->context.active++; |
| if (prev) { |
| pr_hardcont(" (old=0x%p a=%d)", prev, prev->context.active); |
| WARN_ON(prev->context.active < 1); |
| prev->context.active--; |
| } |
| |
| again: |
| #endif /* CONFIG_SMP */ |
| |
| /* If we already have a valid assigned context, skip all that */ |
| id = next->context.id; |
| if (likely(id != MMU_NO_CONTEXT)) { |
| #ifdef DEBUG_MAP_CONSISTENCY |
| if (context_mm[id] != next) |
| pr_err("MMU: mm 0x%p has id %d but context_mm[%d] says 0x%p\n", |
| next, id, id, context_mm[id]); |
| #endif |
| 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) { |
| #ifdef CONFIG_SMP |
| if (num_online_cpus() > 1) { |
| id = steal_context_smp(id); |
| if (id == MMU_NO_CONTEXT) |
| goto again; |
| goto stolen; |
| } |
| #endif /* CONFIG_SMP */ |
| 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; |
| pr_hardcont(" | new id=%d,nrf=%d", id, nr_free_contexts); |
| |
| context_check_map(); |
| 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 |
| */ |
| #ifdef CONFIG_SMP |
| if (test_bit(id, stale_map[cpu])) { |
| pr_hardcont(" | stale flush %d [%d..%d]", |
| id, cpu_first_thread_sibling(cpu), |
| cpu_last_thread_sibling(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]); |
| } |
| } |
| #endif |
| |
| /* Flick the MMU and release lock */ |
| pr_hardcont(" -> %d\n", id); |
| set_context(id, next->pgd); |
| 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) |
| { |
| pr_hard("initing context for mm @%p\n", mm); |
| |
| /* |
| * We have MMU_NO_CONTEXT set to be ~0. Hence check |
| * explicitly against context.id == 0. This ensures that we properly |
| * initialize context slice details for newly allocated mm's (which will |
| * have id == 0) and don't alter context slice inherited via fork (which |
| * will have id != 0). |
| */ |
| if (mm->context.id == 0) |
| slice_init_new_context_exec(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; |
| #ifdef DEBUG_MAP_CONSISTENCY |
| mm->context.active = 0; |
| #endif |
| context_mm[id] = NULL; |
| nr_free_contexts++; |
| } |
| raw_spin_unlock_irqrestore(&context_lock, flags); |
| } |
| |
| #ifdef CONFIG_SMP |
| 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; |
| |
| pr_devel("MMU: Allocating stale context map for CPU %d\n", cpu); |
| 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; |
| |
| pr_devel("MMU: Freeing stale context map for CPU %d\n", cpu); |
| 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; |
| } |
| |
| #endif /* CONFIG_SMP */ |
| |
| /* |
| * 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)); |
| #ifdef 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); |
| #endif |
| |
| 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; |
| } |