--- /dev/null
+/* Support for MMIO probes.
+ * Benfit many code from kprobes
+ * (C) 2002 Louis Zhuang <louis.zhuang@intel.com>.
+ * 2007 Alexander Eichner
+ * 2008 Pekka Paalanen <pq@iki.fi>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/list.h>
+#include <linux/rculist.h>
+#include <linux/spinlock.h>
+#include <linux/hash.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/uaccess.h>
+#include <linux/ptrace.h>
+#include <linux/preempt.h>
+#include <linux/percpu.h>
+#include <linux/kdebug.h>
+#include <linux/mutex.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+#include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
+#include <linux/errno.h>
+#include <asm/debugreg.h>
+#include <linux/mmiotrace.h>
+
+#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 */
+ pteval_t 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) and post_kmmio_handler().
+ * Protected by kmmio_lock, when linked into kmmio_page_table.
+ */
+ int count;
+
+ bool scheduled_for_release;
+};
+
+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 *f;
+
+ page &= PAGE_MASK;
+ head = kmmio_page_list(page);
+ list_for_each_entry_rcu(f, head, list) {
+ if (f->page == page)
+ return f;
+ }
+ return NULL;
+}
+
+static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old)
+{
+ pmdval_t v = pmd_val(*pmd);
+ if (clear) {
+ *old = v & _PAGE_PRESENT;
+ v &= ~_PAGE_PRESENT;
+ } else /* presume this has been called with clear==true previously */
+ v |= *old;
+ set_pmd(pmd, __pmd(v));
+}
+
+static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
+{
+ pteval_t v = pte_val(*pte);
+ if (clear) {
+ *old = v & _PAGE_PRESENT;
+ v &= ~_PAGE_PRESENT;
+ } else /* presume this has been called with clear==true previously */
+ v |= *old;
+ set_pte_atomic(pte, __pte(v));
+}
+
+static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
+{
+ unsigned int level;
+ pte_t *pte = lookup_address(f->page, &level);
+
+ if (!pte) {
+ pr_err("no pte for page 0x%08lx\n", f->page);
+ return -1;
+ }
+
+ switch (level) {
+ case PG_LEVEL_2M:
+ clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence);
+ break;
+ case PG_LEVEL_4K:
+ clear_pte_presence(pte, clear, &f->old_presence);
+ break;
+ default:
+ pr_err("unexpected page level 0x%x.\n", level);
+ return -1;
+ }
+
+ __flush_tlb_one(f->page);
+ 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 pr_fmt("kmmio page already armed.\n"));
+ if (f->armed) {
+ pr_warning("double-arm: page 0x%08lx, ref %d, old %d\n",
+ f->page, f->count, !!f->old_presence);
+ }
+ ret = clear_page_presence(f, true);
+ WARN_ONCE(ret < 0, KERN_ERR pr_fmt("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)
+{
+ int ret = clear_page_presence(f, false);
+ 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 throughout 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) {
+ if (addr == ctx->addr) {
+ /*
+ * A second fault on the same page means some other
+ * condition needs handling by do_page_fault(), the
+ * page really not being present is the most common.
+ */
+ pr_debug("secondary hit for 0x%08lx CPU %d.\n",
+ addr, smp_processor_id());
+
+ if (!faultpage->old_presence)
+ pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n",
+ addr, smp_processor_id());
+ } else {
+ /*
+ * Prevent overwriting already in-flight context.
+ * This should not happen, let's hope disarming at
+ * least prevents a panic.
+ */
+ pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n",
+ smp_processor_id(), addr);
+ pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr);
+ disarm_kmmio_fault_page(faultpage);
+ }
+ 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 throughout 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) {
+ /*
+ * debug traps without an active context are due to either
+ * something external causing them (f.e. using a debugger while
+ * mmio tracing enabled), or erroneous behaviour
+ */
+ pr_warning("unexpected 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);
+
+ /* Prevent racing against release_kmmio_fault_page(). */
+ spin_lock(&kmmio_lock);
+ if (ctx->fpage->count)
+ arm_kmmio_fault_page(ctx->fpage);
+ spin_unlock(&kmmio_lock);
+
+ 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);
+ if (!f->scheduled_for_release) {
+ f->release_next = *release_list;
+ *release_list = f;
+ f->scheduled_for_release = true;
+ }
+ }
+}
+
+/*
+ * 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("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 *f = dr->release_list;
+ while (f) {
+ struct kmmio_fault_page *next = f->release_next;
+ BUG_ON(f->count);
+ kfree(f);
+ f = 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 *f = dr->release_list;
+ struct kmmio_fault_page **prevp = &dr->release_list;
+ unsigned long flags;
+
+ spin_lock_irqsave(&kmmio_lock, flags);
+ while (f) {
+ if (!f->count) {
+ list_del_rcu(&f->list);
+ prevp = &f->release_next;
+ } else {
+ *prevp = f->release_next;
+ f->release_next = NULL;
+ f->scheduled_for_release = false;
+ }
+ f = *prevp;
+ }
+ 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()
+ * Actually 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);
+
+ if (!release_list)
+ return;
+
+ drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
+ if (!drelease) {
+ pr_crit("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;
+ unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
+
+ if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
+ if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
+ /*
+ * Reset the BS bit in dr6 (pointed by args->err) to
+ * denote completion of processing
+ */
+ *dr6_p &= ~DR_STEP;
+ return NOTIFY_STOP;
+ }
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block nb_die = {
+ .notifier_call = kmmio_die_notifier
+};
+
+int kmmio_init(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);
+}
+
+void kmmio_cleanup(void)
+{
+ int i;
+
+ unregister_die_notifier(&nb_die);
+ for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) {
+ WARN_ONCE(!list_empty(&kmmio_page_table[i]),
+ KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n");
+ }
+}
Code Review / kvmfornfv.git / blobdiff