diff options
Diffstat (limited to 'arch/powerpc/mm/nohash/mmu_context.c')
| -rw-r--r-- | arch/powerpc/mm/nohash/mmu_context.c | 493 |
1 files changed, 493 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 000000000000..aac81c9f84a5 --- /dev/null +++ b/arch/powerpc/mm/nohash/mmu_context.c @@ -0,0 +1,493 @@ +// 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; +} |