1 files changed, 364 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
new file mode 100644
index 000000000000..5ecd0401cdb1
--- /dev/null
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -0,0 +1,364 @@
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers. Derived from
+ * "arch/x86/kernel/hw_breakpoint.c"
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright 2010 IBM Corporation
+ * Author: K.Prasad <prasad@linux.vnet.ibm.com>
+ *
+ */
+
+#include <linux/hw_breakpoint.h>
+#include <linux/notifier.h>
+#include <linux/kprobes.h>
+#include <linux/percpu.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+#include <asm/sstep.h>
+#include <asm/uaccess.h>
+
+/*
+ * Stores the breakpoints currently in use on each breakpoint address
+ * register for every cpu
+ */
+static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
+
+/*
+ * Returns total number of data or instruction breakpoints available.
+ */
+int hw_breakpoint_slots(int type)
+{
+        if (type == TYPE_DATA)
+                return HBP_NUM;
+        return 0;               /* no instruction breakpoints available */
+}
+
+/*
+ * Install a perf counter breakpoint.
+ *
+ * We seek a free debug address register and use it for this
+ * breakpoint.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+        struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+        struct perf_event **slot = &__get_cpu_var(bp_per_reg);
+
+        *slot = bp;
+
+        /*
+         * Do not install DABR values if the instruction must be single-stepped.
+         * If so, DABR will be populated in single_step_dabr_instruction().
+         */
+        if (current->thread.last_hit_ubp != bp)
+                set_dabr(info->address | info->type | DABR_TRANSLATION);
+
+        return 0;
+}
+
+/*
+ * Uninstall the breakpoint contained in the given counter.
+ *
+ * First we search the debug address register it uses and then we disable
+ * it.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+        struct perf_event **slot = &__get_cpu_var(bp_per_reg);
+
+        if (*slot != bp) {
+                WARN_ONCE(1, "Can't find the breakpoint");
+                return;
+        }
+
+        *slot = NULL;
+        set_dabr(0);
+}
+
+/*
+ * Perform cleanup of arch-specific counters during unregistration
+ * of the perf-event
+ */
+void arch_unregister_hw_breakpoint(struct perf_event *bp)
+{
+        /*
+         * If the breakpoint is unregistered between a hw_breakpoint_handler()
+         * and the single_step_dabr_instruction(), then cleanup the breakpoint
+         * restoration variables to prevent dangling pointers.
+         */
+        if (bp->ctx->task)
+                bp->ctx->task->thread.last_hit_ubp = NULL;
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+        struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+        return is_kernel_addr(info->address);
+}
+
+int arch_bp_generic_fields(int type, int *gen_bp_type)
+{
+        switch (type) {
+        case DABR_DATA_READ:
+                *gen_bp_type = HW_BREAKPOINT_R;
+                break;
+        case DABR_DATA_WRITE:
+                *gen_bp_type = HW_BREAKPOINT_W;
+                break;
+        case (DABR_DATA_WRITE | DABR_DATA_READ):
+                *gen_bp_type = (HW_BREAKPOINT_W | HW_BREAKPOINT_R);
+                break;
+        default:
+                return -EINVAL;
+        }
+        return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+        int ret = -EINVAL;
+        struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+        if (!bp)
+                return ret;
+
+        switch (bp->attr.bp_type) {
+        case HW_BREAKPOINT_R:
+                info->type = DABR_DATA_READ;
+                break;
+        case HW_BREAKPOINT_W:
+                info->type = DABR_DATA_WRITE;
+                break;
+        case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
+                info->type = (DABR_DATA_READ | DABR_DATA_WRITE);
+                break;
+        default:
+                return ret;
+        }
+
+        info->address = bp->attr.bp_addr;
+        info->len = bp->attr.bp_len;
+
+        /*
+         * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
+         * and breakpoint addresses are aligned to nearest double-word
+         * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
+         * 'symbolsize' should satisfy the check below.
+         */
+        if (info->len >
+            (HW_BREAKPOINT_LEN - (info->address & HW_BREAKPOINT_ALIGN)))
+                return -EINVAL;
+        return 0;
+}
+
+/*
+ * Restores the breakpoint on the debug registers.
+ * Invoke this function if it is known that the execution context is
+ * about to change to cause loss of MSR_SE settings.
+ */
+void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
+{
+        struct arch_hw_breakpoint *info;
+
+        if (likely(!tsk->thread.last_hit_ubp))
+                return;
+
+        info = counter_arch_bp(tsk->thread.last_hit_ubp);
+        regs->msr &= ~MSR_SE;
+        set_dabr(info->address | info->type | DABR_TRANSLATION);
+        tsk->thread.last_hit_ubp = NULL;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+        int rc = NOTIFY_STOP;
+        struct perf_event *bp;
+        struct pt_regs *regs = args->regs;
+        int stepped = 1;
+        struct arch_hw_breakpoint *info;
+        unsigned int instr;
+        unsigned long dar = regs->dar;
+
+        /* Disable breakpoints during exception handling */
+        set_dabr(0);
+
+        /*
+         * The counter may be concurrently released but that can only
+         * occur from a call_rcu() path. We can then safely fetch
+         * the breakpoint, use its callback, touch its counter
+         * while we are in an rcu_read_lock() path.
+         */
+        rcu_read_lock();
+
+        bp = __get_cpu_var(bp_per_reg);
+        if (!bp)
+                goto out;
+        info = counter_arch_bp(bp);
+
+        /*
+         * Return early after invoking user-callback function without restoring
+         * DABR if the breakpoint is from ptrace which always operates in
+         * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
+         * generated in do_dabr().
+         */
+        if (bp->overflow_handler == ptrace_triggered) {
+                perf_bp_event(bp, regs);
+                rc = NOTIFY_DONE;
+                goto out;
+        }
+
+        /*
+         * Verify if dar lies within the address range occupied by the symbol
+         * being watched to filter extraneous exceptions.  If it doesn't,
+         * we still need to single-step the instruction, but we don't
+         * generate an event.
+         */
+        info->extraneous_interrupt = !((bp->attr.bp_addr <= dar) &&
+                        (dar - bp->attr.bp_addr < bp->attr.bp_len));
+
+        /* Do not emulate user-space instructions, instead single-step them */
+        if (user_mode(regs)) {
+                bp->ctx->task->thread.last_hit_ubp = bp;
+                regs->msr |= MSR_SE;
+                goto out;
+        }
+
+        stepped = 0;
+        instr = 0;
+        if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
+                stepped = emulate_step(regs, instr);
+
+        /*
+         * emulate_step() could not execute it. We've failed in reliably
+         * handling the hw-breakpoint. Unregister it and throw a warning
+         * message to let the user know about it.
+         */
+        if (!stepped) {
+                WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
+                        "0x%lx will be disabled.", info->address);
+                perf_event_disable(bp);
+                goto out;
+        }
+        /*
+         * As a policy, the callback is invoked in a 'trigger-after-execute'
+         * fashion
+         */
+        if (!info->extraneous_interrupt)
+                perf_bp_event(bp, regs);
+
+        set_dabr(info->address | info->type | DABR_TRANSLATION);
+out:
+        rcu_read_unlock();
+        return rc;
+}
+
+/*
+ * Handle single-step exceptions following a DABR hit.
+ */
+int __kprobes single_step_dabr_instruction(struct die_args *args)
+{
+        struct pt_regs *regs = args->regs;
+        struct perf_event *bp = NULL;
+        struct arch_hw_breakpoint *bp_info;
+
+        bp = current->thread.last_hit_ubp;
+        /*
+         * Check if we are single-stepping as a result of a
+         * previous HW Breakpoint exception
+         */
+        if (!bp)
+                return NOTIFY_DONE;
+
+        bp_info = counter_arch_bp(bp);
+
+        /*
+         * We shall invoke the user-defined callback function in the single
+         * stepping handler to confirm to 'trigger-after-execute' semantics
+         */
+        if (!bp_info->extraneous_interrupt)
+                perf_bp_event(bp, regs);
+
+        set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
+        current->thread.last_hit_ubp = NULL;
+
+        /*
+         * If the process was being single-stepped by ptrace, let the
+         * other single-step actions occur (e.g. generate SIGTRAP).
+         */
+        if (test_thread_flag(TIF_SINGLESTEP))
+                return NOTIFY_DONE;
+
+        return NOTIFY_STOP;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_exceptions_notify(
+                struct notifier_block *unused, unsigned long val, void *data)
+{
+        int ret = NOTIFY_DONE;
+
+        switch (val) {
+        case DIE_DABR_MATCH:
+                ret = hw_breakpoint_handler(data);
+                break;
+        case DIE_SSTEP:
+                ret = single_step_dabr_instruction(data);
+                break;
+        }
+
+        return ret;
+}
+
+/*
+ * Release the user breakpoints used by ptrace
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+        struct thread_struct *t = &tsk->thread;
+
+        unregister_hw_breakpoint(t->ptrace_bps[0]);
+        t->ptrace_bps[0] = NULL;
+}
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+        /* TODO */
+}