--- /dev/null
+/*
+ * 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/sched.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 = this_cpu_ptr(&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_breakpoint(info);
+
+ 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 = this_cpu_ptr(&bp_per_reg);
+
+ if (*slot != bp) {
+ WARN_ONCE(1, "Can't find the breakpoint");
+ return;
+ }
+
+ *slot = NULL;
+ hw_breakpoint_disable();
+}
+
+/*
+ * 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 && 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)
+{
+ *gen_bp_type = 0;
+ if (type & HW_BRK_TYPE_READ)
+ *gen_bp_type |= HW_BREAKPOINT_R;
+ if (type & HW_BRK_TYPE_WRITE)
+ *gen_bp_type |= HW_BREAKPOINT_W;
+ if (*gen_bp_type == 0)
+ return -EINVAL;
+ return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+ int ret = -EINVAL, length_max;
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+ if (!bp)
+ return ret;
+
+ info->type = HW_BRK_TYPE_TRANSLATE;
+ if (bp->attr.bp_type & HW_BREAKPOINT_R)
+ info->type |= HW_BRK_TYPE_READ;
+ if (bp->attr.bp_type & HW_BREAKPOINT_W)
+ info->type |= HW_BRK_TYPE_WRITE;
+ if (info->type == HW_BRK_TYPE_TRANSLATE)
+ /* must set alteast read or write */
+ return ret;
+ if (!(bp->attr.exclude_user))
+ info->type |= HW_BRK_TYPE_USER;
+ if (!(bp->attr.exclude_kernel))
+ info->type |= HW_BRK_TYPE_KERNEL;
+ if (!(bp->attr.exclude_hv))
+ info->type |= HW_BRK_TYPE_HYP;
+ 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.
+ */
+ length_max = 8; /* DABR */
+ if (cpu_has_feature(CPU_FTR_DAWR)) {
+ length_max = 512 ; /* 64 doublewords */
+ /* DAWR region can't cross 512 boundary */
+ if ((bp->attr.bp_addr >> 10) !=
+ ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
+ return -EINVAL;
+ }
+ if (info->len >
+ (length_max - (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_breakpoint(info);
+ 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 */
+ hw_breakpoint_disable();
+
+ /*
+ * 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 = __this_cpu_read(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->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
+ if (!((bp->attr.bp_addr <= dar) &&
+ (dar - bp->attr.bp_addr < bp->attr.bp_len)))
+ info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
+
+ /* Do not emulate user-space instructions, instead single-step them */
+ if (user_mode(regs)) {
+ current->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->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
+ perf_bp_event(bp, regs);
+
+ __set_breakpoint(info);
+out:
+ rcu_read_unlock();
+ return rc;
+}
+
+/*
+ * Handle single-step exceptions following a DABR hit.
+ */
+static 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 *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;
+
+ 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 (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
+ perf_bp_event(bp, regs);
+
+ __set_breakpoint(info);
+ 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 */
+}
Code Review / kvmfornfv.git / blobdiff