/* Support for MMIO probes. * Benfit many code from kprobes * (C) 2002 Louis Zhuang . * 2007 Alexander Eichner * 2008 Pekka Paalanen */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define KMMIO_PAGE_HASH_BITS 4 #define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS) struct kmmio_fault_page { struct list_head list; struct kmmio_fault_page *release_next; unsigned long page; /* location of the fault page */ bool old_presence; /* page presence prior to arming */ bool armed; /* * Number of times this page has been registered as a part * of a probe. If zero, page is disarmed and this may be freed. * Used only by writers (RCU). */ int count; }; struct kmmio_delayed_release { struct rcu_head rcu; struct kmmio_fault_page *release_list; }; struct kmmio_context { struct kmmio_fault_page *fpage; struct kmmio_probe *probe; unsigned long saved_flags; unsigned long addr; int active; }; static DEFINE_SPINLOCK(kmmio_lock); /* Protected by kmmio_lock */ unsigned int kmmio_count; /* Read-protected by RCU, write-protected by kmmio_lock. */ static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE]; static LIST_HEAD(kmmio_probes); static struct list_head *kmmio_page_list(unsigned long page) { return &kmmio_page_table[hash_long(page, KMMIO_PAGE_HASH_BITS)]; } /* Accessed per-cpu */ static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx); /* * this is basically a dynamic stabbing problem: * Could use the existing prio tree code or * Possible better implementations: * The Interval Skip List: A Data Structure for Finding All Intervals That * Overlap a Point (might be simple) * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup */ /* Get the kmmio at this addr (if any). You must be holding RCU read lock. */ static struct kmmio_probe *get_kmmio_probe(unsigned long addr) { struct kmmio_probe *p; list_for_each_entry_rcu(p, &kmmio_probes, list) { if (addr >= p->addr && addr <= (p->addr + p->len)) return p; } return NULL; } /* You must be holding RCU read lock. */ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page) { struct list_head *head; struct kmmio_fault_page *p; page &= PAGE_MASK; head = kmmio_page_list(page); list_for_each_entry_rcu(p, head, list) { if (p->page == page) return p; } return NULL; } static void set_pmd_presence(pmd_t *pmd, bool present, bool *old) { pmdval_t v = pmd_val(*pmd); *old = !!(v & _PAGE_PRESENT); v &= ~_PAGE_PRESENT; if (present) v |= _PAGE_PRESENT; set_pmd(pmd, __pmd(v)); } static void set_pte_presence(pte_t *pte, bool present, bool *old) { pteval_t v = pte_val(*pte); *old = !!(v & _PAGE_PRESENT); v &= ~_PAGE_PRESENT; if (present) v |= _PAGE_PRESENT; set_pte_atomic(pte, __pte(v)); } static int set_page_presence(unsigned long addr, bool present, bool *old) { unsigned int level; pte_t *pte = lookup_address(addr, &level); if (!pte) { pr_err("kmmio: no pte for page 0x%08lx\n", addr); return -1; } switch (level) { case PG_LEVEL_2M: set_pmd_presence((pmd_t *)pte, present, old); break; case PG_LEVEL_4K: set_pte_presence(pte, present, old); break; default: pr_err("kmmio: unexpected page level 0x%x.\n", level); return -1; } __flush_tlb_one(addr); return 0; } /* * Mark the given page as not present. Access to it will trigger a fault. * * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the * protection is ignored here. RCU read lock is assumed held, so the struct * will not disappear unexpectedly. Furthermore, the caller must guarantee, * that double arming the same virtual address (page) cannot occur. * * Double disarming on the other hand is allowed, and may occur when a fault * and mmiotrace shutdown happen simultaneously. */ static int arm_kmmio_fault_page(struct kmmio_fault_page *f) { int ret; WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n"); if (f->armed) { pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n", f->page, f->count, f->old_presence); } ret = set_page_presence(f->page, false, &f->old_presence); WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page); f->armed = true; return ret; } /** Restore the given page to saved presence state. */ static void disarm_kmmio_fault_page(struct kmmio_fault_page *f) { bool tmp; int ret = set_page_presence(f->page, f->old_presence, &tmp); WARN_ONCE(ret < 0, KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page); f->armed = false; } /* * This is being called from do_page_fault(). * * We may be in an interrupt or a critical section. Also prefecthing may * trigger a page fault. We may be in the middle of process switch. * We cannot take any locks, because we could be executing especially * within a kmmio critical section. * * Local interrupts are disabled, so preemption cannot happen. * Do not enable interrupts, do not sleep, and watch out for other CPUs. */ /* * Interrupts are disabled on entry as trap3 is an interrupt gate * and they remain disabled thorough out this function. */ int kmmio_handler(struct pt_regs *regs, unsigned long addr) { struct kmmio_context *ctx; struct kmmio_fault_page *faultpage; int ret = 0; /* default to fault not handled */ /* * Preemption is now disabled to prevent process switch during * single stepping. We can only handle one active kmmio trace * per cpu, so ensure that we finish it before something else * gets to run. We also hold the RCU read lock over single * stepping to avoid looking up the probe and kmmio_fault_page * again. */ preempt_disable(); rcu_read_lock(); faultpage = get_kmmio_fault_page(addr); if (!faultpage) { /* * Either this page fault is not caused by kmmio, or * another CPU just pulled the kmmio probe from under * our feet. The latter case should not be possible. */ goto no_kmmio; } ctx = &get_cpu_var(kmmio_ctx); if (ctx->active) { disarm_kmmio_fault_page(faultpage); if (addr == ctx->addr) { /* * On SMP we sometimes get recursive probe hits on the * same address. Context is already saved, fall out. */ pr_debug("kmmio: duplicate probe hit on CPU %d, for " "address 0x%08lx.\n", smp_processor_id(), addr); ret = 1; goto no_kmmio_ctx; } /* * Prevent overwriting already in-flight context. * This should not happen, let's hope disarming at least * prevents a panic. */ pr_emerg("kmmio: recursive probe hit on CPU %d, " "for address 0x%08lx. Ignoring.\n", smp_processor_id(), addr); pr_emerg("kmmio: previous hit was at 0x%08lx.\n", ctx->addr); goto no_kmmio_ctx; } ctx->active++; ctx->fpage = faultpage; ctx->probe = get_kmmio_probe(addr); ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF)); ctx->addr = addr; if (ctx->probe && ctx->probe->pre_handler) ctx->probe->pre_handler(ctx->probe, regs, addr); /* * Enable single-stepping and disable interrupts for the faulting * context. Local interrupts must not get enabled during stepping. */ regs->flags |= X86_EFLAGS_TF; regs->flags &= ~X86_EFLAGS_IF; /* Now we set present bit in PTE and single step. */ disarm_kmmio_fault_page(ctx->fpage); /* * If another cpu accesses the same page while we are stepping, * the access will not be caught. It will simply succeed and the * only downside is we lose the event. If this becomes a problem, * the user should drop to single cpu before tracing. */ put_cpu_var(kmmio_ctx); return 1; /* fault handled */ no_kmmio_ctx: put_cpu_var(kmmio_ctx); no_kmmio: rcu_read_unlock(); preempt_enable_no_resched(); return ret; } /* * Interrupts are disabled on entry as trap1 is an interrupt gate * and they remain disabled thorough out this function. * This must always get called as the pair to kmmio_handler(). */ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs) { int ret = 0; struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx); if (!ctx->active) { pr_debug("kmmio: spurious debug trap on CPU %d.\n", smp_processor_id()); goto out; } if (ctx->probe && ctx->probe->post_handler) ctx->probe->post_handler(ctx->probe, condition, regs); arm_kmmio_fault_page(ctx->fpage); regs->flags &= ~X86_EFLAGS_TF; regs->flags |= ctx->saved_flags; /* These were acquired in kmmio_handler(). */ ctx->active--; BUG_ON(ctx->active); rcu_read_unlock(); preempt_enable_no_resched(); /* * if somebody else is singlestepping across a probe point, flags * will have TF set, in which case, continue the remaining processing * of do_debug, as if this is not a probe hit. */ if (!(regs->flags & X86_EFLAGS_TF)) ret = 1; out: put_cpu_var(kmmio_ctx); return ret; } /* You must be holding kmmio_lock. */ static int add_kmmio_fault_page(unsigned long page) { struct kmmio_fault_page *f; page &= PAGE_MASK; f = get_kmmio_fault_page(page); if (f) { if (!f->count) arm_kmmio_fault_page(f); f->count++; return 0; } f = kzalloc(sizeof(*f), GFP_ATOMIC); if (!f) return -1; f->count = 1; f->page = page; if (arm_kmmio_fault_page(f)) { kfree(f); return -1; } list_add_rcu(&f->list, kmmio_page_list(f->page)); return 0; } /* You must be holding kmmio_lock. */ static void release_kmmio_fault_page(unsigned long page, struct kmmio_fault_page **release_list) { struct kmmio_fault_page *f; page &= PAGE_MASK; f = get_kmmio_fault_page(page); if (!f) return; f->count--; BUG_ON(f->count < 0); if (!f->count) { disarm_kmmio_fault_page(f); f->release_next = *release_list; *release_list = f; } } /* * With page-unaligned ioremaps, one or two armed pages may contain * addresses from outside the intended mapping. Events for these addresses * are currently silently dropped. The events may result only from programming * mistakes by accessing addresses before the beginning or past the end of a * mapping. */ int register_kmmio_probe(struct kmmio_probe *p) { unsigned long flags; int ret = 0; unsigned long size = 0; const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK); spin_lock_irqsave(&kmmio_lock, flags); if (get_kmmio_probe(p->addr)) { ret = -EEXIST; goto out; } kmmio_count++; list_add_rcu(&p->list, &kmmio_probes); while (size < size_lim) { if (add_kmmio_fault_page(p->addr + size)) pr_err("kmmio: Unable to set page fault.\n"); size += PAGE_SIZE; } out: spin_unlock_irqrestore(&kmmio_lock, flags); /* * XXX: What should I do here? * Here was a call to global_flush_tlb(), but it does not exist * anymore. It seems it's not needed after all. */ return ret; } EXPORT_SYMBOL(register_kmmio_probe); static void rcu_free_kmmio_fault_pages(struct rcu_head *head) { struct kmmio_delayed_release *dr = container_of( head, struct kmmio_delayed_release, rcu); struct kmmio_fault_page *p = dr->release_list; while (p) { struct kmmio_fault_page *next = p->release_next; BUG_ON(p->count); kfree(p); p = next; } kfree(dr); } static void remove_kmmio_fault_pages(struct rcu_head *head) { struct kmmio_delayed_release *dr = container_of( head, struct kmmio_delayed_release, rcu); struct kmmio_fault_page *p = dr->release_list; struct kmmio_fault_page **prevp = &dr->release_list; unsigned long flags; spin_lock_irqsave(&kmmio_lock, flags); while (p) { if (!p->count) list_del_rcu(&p->list); else *prevp = p->release_next; prevp = &p->release_next; p = p->release_next; } spin_unlock_irqrestore(&kmmio_lock, flags); /* This is the real RCU destroy call. */ call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages); } /* * Remove a kmmio probe. You have to synchronize_rcu() before you can be * sure that the callbacks will not be called anymore. Only after that * you may actually release your struct kmmio_probe. * * Unregistering a kmmio fault page has three steps: * 1. release_kmmio_fault_page() * Disarm the page, wait a grace period to let all faults finish. * 2. remove_kmmio_fault_pages() * Remove the pages from kmmio_page_table. * 3. rcu_free_kmmio_fault_pages() * Actally free the kmmio_fault_page structs as with RCU. */ void unregister_kmmio_probe(struct kmmio_probe *p) { unsigned long flags; unsigned long size = 0; const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK); struct kmmio_fault_page *release_list = NULL; struct kmmio_delayed_release *drelease; spin_lock_irqsave(&kmmio_lock, flags); while (size < size_lim) { release_kmmio_fault_page(p->addr + size, &release_list); size += PAGE_SIZE; } list_del_rcu(&p->list); kmmio_count--; spin_unlock_irqrestore(&kmmio_lock, flags); drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC); if (!drelease) { pr_crit("kmmio: leaking kmmio_fault_page objects.\n"); return; } drelease->release_list = release_list; /* * This is not really RCU here. We have just disarmed a set of * pages so that they cannot trigger page faults anymore. However, * we cannot remove the pages from kmmio_page_table, * because a probe hit might be in flight on another CPU. The * pages are collected into a list, and they will be removed from * kmmio_page_table when it is certain that no probe hit related to * these pages can be in flight. RCU grace period sounds like a * good choice. * * If we removed the pages too early, kmmio page fault handler might * not find the respective kmmio_fault_page and determine it's not * a kmmio fault, when it actually is. This would lead to madness. */ call_rcu(&drelease->rcu, remove_kmmio_fault_pages); } EXPORT_SYMBOL(unregister_kmmio_probe); static int kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args) { struct die_args *arg = args; if (val == DIE_DEBUG && (arg->err & DR_STEP)) if (post_kmmio_handler(arg->err, arg->regs) == 1) return NOTIFY_STOP; return NOTIFY_DONE; } static struct notifier_block nb_die = { .notifier_call = kmmio_die_notifier }; static int __init init_kmmio(void) { int i; for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) INIT_LIST_HEAD(&kmmio_page_table[i]); return register_die_notifier(&nb_die); } fs_initcall(init_kmmio); /* should be before device_initcall() */