[RFC Patch 0/9] Hardware Breakpoint interfaces

[RFC Patch 0/9] Hardware Breakpoint interfaces

[K.Prasad]

Hi All,
	In the ensuing mails, please find the patches that provide
interfaces to use Hardware Breakpoint (or Hardware watchpoint registers)
for addresses in kernel- and user-space.

This work is primarily based on the patches that were discussed earlier
on Linux Kernel Mailing List (http://lkml.org/lkml/2007/3/2/221) through
a discussion initiated by Alan Stern and carried forward with extensive
help from Roland McGrath (copied). They now ported to the most recent
kernel version (2.6.27-rc9) along with changes to the invocation of
'@triggered' function (presently split into pre_ and post_handler
routines).

These patches add a new feature to the kernel i.e. use HW breakpoint
registers to watch kernel-space data (for read/write operations) and
kernel instructions for execute operations. The interfaces introduced
through these patches for handling HW Breakpoint registers, namely
(un)register_<kernel/user>_hw_breakpoint() are intended to serve as
core-routines that will interact with the hardware registers directly,
while the users of breakpoint registers will do so through these
interfaces. Given the large number of such users in the kernel (such
as KGDB, KVM for kernel-space), not all of them have been modified
to use the proposed interfaces - atleast in this iteration of patches.

The patches are marked as [RFC], meaning that there is plenty of
'work-in-progress' and here is a near-exhaustive list of them:

- Enable KGDB and KVM to use the register_kernel_hw_breakpoint()
  interface for their HW Breakpoint usage, in the absence of which
  they will be broken during simultaneous use.
- Stress test the patches to study the behaviour during multiple
  requests from various sources/requests beyond available number of
  registers.
- Support multiple handlers for a given breakpoint in kernel- or
  user-space address.
- Provide complete breakpoint functionality in x86 i.e. include
  breakpoints on I/O operations.
- Addition of Documentation/hw_bkpt.txt and samples/hw_breakpoint/*.c
  files for better readability.
- Code re-arrangement to avoid the #include of kernel/hw_breakpoint.c in
  arch/x86/kernel/hw_breakpoint.c

Thanks,
K.Prasad

[RFC Patch 1/9] Introducing generic hardware breakpoint handler interfaces

[K.Prasad]

This patch introduces two new files hw_breakpoint.[ch] which defines the 
generic interfaces to use hardware breakpoint infrastructure of the system. 

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 include/asm-generic/hw_breakpoint.h |  236 +++++++++++
 kernel/hw_breakpoint.c              |  731 ++++++++++++++++++++++++++++++++++++
 2 files changed, 967 insertions(+)

Index: linux-bkpt-lkml-27-rc9/include/asm-generic/hw_breakpoint.h
===================================================================
--- /dev/null
+++ linux-bkpt-lkml-27-rc9/include/asm-generic/hw_breakpoint.h
@@ -0,0 +1,236 @@
+#ifndef	_ASM_GENERIC_HW_BREAKPOINT_H
+#define	_ASM_GENERIC_HW_BREAKPOINT_H
+
+#ifndef __ARCH_HW_BREAKPOINT_H
+#error "Please don't include this file directly"
+#endif
+
+#ifdef	__KERNEL__
+#include <linux/list.h>
+#include <linux/types.h>
+
+/**
+ * struct hw_breakpoint - unified kernel/user-space hardware breakpoint
+ * @node: internal linked-list management
+ * @triggered: callback invoked when the breakpoint is hit
+ * @installed: callback invoked when the breakpoint is installed
+ * @uninstalled: callback invoked when the breakpoint is uninstalled
+ * @info: arch-specific breakpoint info (address, length, and type)
+ * @priority: requested priority level
+ * @status: current registration/installation status
+ *
+ * %hw_breakpoint structures are the kernel's way of representing
+ * hardware breakpoints.  These can be either execute breakpoints
+ * (triggered on instruction execution) or data breakpoints (also known
+ * as "watchpoints", triggered on data access), and the breakpoint's
+ * target address can be located in either kernel space or user space.
+ *
+ * The breakpoint's address, length, and type are highly
+ * architecture-specific.  The values are encoded in the @info field; you
+ * specify them when registering the breakpoint.  To examine the encoded
+ * values use hw_breakpoint_get_{kaddress,uaddress,len,type}(), declared
+ * below.
+ *
+ * The address is specified as a regular kernel pointer (for kernel-space
+ * breakponts) or as an %__user pointer (for user-space breakpoints).
+ * With register_user_hw_breakpoint(), the address must refer to a
+ * location in user space.  The breakpoint will be active only while the
+ * requested task is running.  Conversely with
+ * register_kernel_hw_breakpoint(), the address must refer to a location
+ * in kernel space, and the breakpoint will be active on all CPUs
+ * regardless of the current task.
+ *
+ * The length is the breakpoint's extent in bytes, which is subject to
+ * certain limitations.  include/asm/hw_breakpoint.h contains macros
+ * defining the available lengths for a specific architecture.  Note that
+ * the address's alignment must match the length.  The breakpoint will
+ * catch accesses to any byte in the range from address to address +
+ * (length - 1).
+ *
+ * The breakpoint's type indicates the sort of access that will cause it
+ * to trigger.  Possible values may include:
+ *
+ * 	%HW_BREAKPOINT_EXECUTE (triggered on instruction execution),
+ * 	%HW_BREAKPOINT_RW (triggered on read or write access),
+ * 	%HW_BREAKPOINT_WRITE (triggered on write access), and
+ * 	%HW_BREAKPOINT_READ (triggered on read access).
+ *
+ * Appropriate macros are defined in include/asm/hw_breakpoint.h; not all
+ * possibilities are available on all architectures.  Execute breakpoints
+ * must have length equal to the special value %HW_BREAKPOINT_LEN_EXECUTE.
+ *
+ * When a breakpoint gets hit, the @triggered callback is invoked
+ * in_interrupt with a pointer to the %hw_breakpoint structure and the
+ * processor registers.  Execute-breakpoint traps occur before the
+ * breakpointed instruction runs; when the callback returns the
+ * instruction is restarted (this time without a debug exception).  All
+ * other types of trap occur after the memory access has taken place.
+ * Breakpoints are disabled while @triggered runs, to avoid recursive
+ * traps and allow unhindered access to breakpointed memory.
+ *
+ * Hardware breakpoints are implemented using the CPU's debug registers,
+ * which are a limited hardware resource.  Requests to register a
+ * breakpoint will always succeed provided the parameters are valid,
+ * but the breakpoint may not be installed in a debug register right
+ * away.  Physical debug registers are allocated based on the priority
+ * level stored in @priority (higher values indicate higher priority).
+ * User-space breakpoints within a single thread compete with one
+ * another, and all user-space breakpoints compete with all kernel-space
+ * breakpoints; however user-space breakpoints in different threads do
+ * not compete.  %HW_BREAKPOINT_PRIO_PTRACE is the level used for ptrace
+ * requests; an unobtrusive kernel-space breakpoint will use
+ * %HW_BREAKPOINT_PRIO_NORMAL to avoid disturbing user programs.  A
+ * kernel-space breakpoint that always wants to be installed and doesn't
+ * care about disrupting user debugging sessions can specify
+ * %HW_BREAKPOINT_PRIO_HIGH.
+ *
+ * A particular breakpoint may be allocated (installed in) a debug
+ * register or deallocated (uninstalled) from its debug register at any
+ * time, as other breakpoints are registered and unregistered.  The
+ * @installed and @uninstalled callbacks are invoked in_atomic when these
+ * events occur.  It is legal for @installed or @uninstalled to be %NULL,
+ * however @triggered must not be.  Note that it is not possible to
+ * register or unregister a user-space breakpoint from within a callback
+ * routine, since doing so requires a process context.  Note that for user
+ * breakpoints, while in @installed and @uninstalled the thread may be context
+ * switched. Hence it may not be safe to call printk().
+ *
+ * For kernel-space breakpoints, @installed is invoked after the
+ * breakpoint is actually installed and @uninstalled is invoked before
+ * the breakpoint is actually uninstalled.  As a result @triggered can
+ * be called when you may not expect it, but this way you will know that
+ * during the time interval from @installed to @uninstalled, all events
+ * are faithfully reported.  (It is not possible to do any better than
+ * this in general, because on SMP systems there is no way to set a debug
+ * register simultaneously on all CPUs.)  The same isn't always true with
+ * user-space breakpoints, but the differences should not be visible to a
+ * user process.
+ *
+ * If you need to know whether your kernel-space breakpoint was installed
+ * immediately upon registration, you can check the return value from
+ * register_kernel_hw_breakpoint().  If the value is not > 0, you can
+ * give up and unregister the breakpoint right away.
+ *
+ * @node and @status are intended for internal use.  However @status
+ * may be read to determine whether or not the breakpoint is currently
+ * installed.  (The value is not reliable unless local interrupts are
+ * disabled.)
+ *
+ * This sample code sets a breakpoint on pid_max and registers a callback
+ * function for writes to that variable.  Note that it is not portable
+ * as written, because not all architectures support HW_BREAKPOINT_LEN_4.
+ *
+ * ----------------------------------------------------------------------
+ *
+ * #include <asm/hw_breakpoint.h>
+ *
+ * static void triggered(struct hw_breakpoint *bp, struct pt_regs *regs)
+ * {
+ * 	printk(KERN_DEBUG "Breakpoint triggered\n");
+ * 	dump_stack();
+ *  	.......<more debugging output>........
+ * }
+ *
+ * static struct hw_breakpoint my_bp;
+ *
+ * static int init_module(void)
+ * {
+ *	..........<do anything>............
+ *	my_bp.triggered = triggered;
+ *	my_bp.priority = HW_BREAKPOINT_PRIO_NORMAL;
+ *	rc = register_kernel_hw_breakpoint(&my_bp, &pid_max,
+ *			HW_BREAKPOINT_LEN_4, HW_BREAKPOINT_WRITE);
+ *	..........<do anything>............
+ * }
+ *
+ * static void cleanup_module(void)
+ * {
+ *	..........<do anything>............
+ *	unregister_kernel_hw_breakpoint(&my_bp);
+ *	..........<do anything>............
+ * }
+ *
+ * ----------------------------------------------------------------------
+ *
+ */
+struct hw_breakpoint {
+	struct list_head	node;
+	void		(*pre_handler)(struct hw_breakpoint *,
+							struct pt_regs *);
+	void		(*post_handler)(struct hw_breakpoint *,
+							struct pt_regs *);
+	void		(*installed)(struct hw_breakpoint *);
+	void		(*uninstalled)(struct hw_breakpoint *);
+	struct arch_hw_breakpoint	info;
+	u8		priority;
+	u8		status;
+};
+
+/*
+ * Inline accessor routines to retrieve the arch-specific parts of
+ * a breakpoint structure:
+ */
+static const void *hw_breakpoint_get_kaddress(struct hw_breakpoint *bp);
+static const void __user *hw_breakpoint_get_uaddress(struct hw_breakpoint *bp);
+static unsigned hw_breakpoint_get_len(struct hw_breakpoint *bp);
+static unsigned hw_breakpoint_get_type(struct hw_breakpoint *bp);
+
+/*
+ * len and type values are defined in include/asm/hw_breakpoint.h.
+ * Available values vary according to the architecture.  On i386 the
+ * possibilities are:
+ *
+ *	HW_BREAKPOINT_LEN_1
+ *	HW_BREAKPOINT_LEN_2
+ *	HW_BREAKPOINT_LEN_4
+ *	HW_BREAKPOINT_LEN_EXECUTE
+ *	HW_BREAKPOINT_RW
+ *	HW_BREAKPOINT_READ
+ *	HW_BREAKPOINT_EXECUTE
+ *
+ * On other architectures HW_BREAKPOINT_LEN_8 may be available, and the
+ * 1-, 2-, and 4-byte lengths may be unavailable.  There also may be
+ * HW_BREAKPOINT_WRITE.  You can use #ifdef to check at compile time.
+ */
+
+/* Standard HW breakpoint priority levels (higher value = higher priority) */
+#define HW_BREAKPOINT_PRIO_NORMAL	25
+#define HW_BREAKPOINT_PRIO_PTRACE	50
+#define HW_BREAKPOINT_PRIO_HIGH		75
+
+/* HW breakpoint status values (0 = not registered) */
+#define HW_BREAKPOINT_REGISTERED	1
+#define HW_BREAKPOINT_INSTALLED		2
+
+/*
+ * The following two routines are meant to be called only from within
+ * the ptrace or utrace subsystems.  The tsk argument will usually be a
+ * process being debugged by the current task, although it is also legal
+ * for tsk to be the current task.  In any case it must be guaranteed
+ * that tsk will not start running in user mode while its breakpoints are
+ * being modified.
+ */
+int register_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp,
+		const void __user *address, unsigned len, unsigned type);
+void unregister_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp);
+
+/*
+ * The following routines help the user determine if the architecture supports
+ * a trigger-before access/execution mechanism or a trigger-after
+ * access/execution. This is dependent on the type of breakpoint and the
+ * architecture
+ */
+int trigger_before_arch(unsigned type);
+int trigger_after_arch(unsigned type);
+
+/*
+ * Kernel breakpoints are not associated with any particular thread.
+ */
+int register_kernel_hw_breakpoint(struct hw_breakpoint *bp,
+		const void *address, unsigned len, unsigned type);
+void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ASM_GENERIC_HW_BREAKPOINT_H */
Index: linux-bkpt-lkml-27-rc9/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ linux-bkpt-lkml-27-rc9/kernel/hw_breakpoint.c
@@ -0,0 +1,731 @@
+/*
+ * 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 (C) 2007 Alan Stern
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ *
+ * This file contains the arch-independent routines.  It is not meant
+ * to be compiled as a standalone source file; rather it should be
+ * #include'd by the arch-specific implementation.
+ */
+
+
+/*
+ * Install the debug register values for a new thread.
+ */
+void switch_to_thread_hw_breakpoint(struct task_struct *tsk)
+{
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	struct cpu_hw_breakpoint *chbi;
+	struct kernel_bp_data *thr_kbpdata;
+
+	/* This routine is on the hot path; it gets called for every
+	 * context switch into a task with active breakpoints.  We
+	 * must make sure that the common case executes as quickly as
+	 * possible.
+	 */
+	chbi = &per_cpu(cpu_info, get_cpu());
+	chbi->bp_task = tsk;
+
+	/* Use RCU to synchronize with external updates */
+	rcu_read_lock();
+
+	/* Other CPUs might be making updates to the list of kernel
+	 * breakpoints at this time.  If they are, they will modify
+	 * the other entry in kbpdata[] -- the one not pointed to
+	 * by chbi->cur_kbpdata.  So the update itself won't affect
+	 * us directly.
+	 *
+	 * However when the update is finished, an IPI will arrive
+	 * telling this CPU to change chbi->cur_kbpdata.  We need
+	 * to use a single consistent kbpdata[] entry, the present one.
+	 * So we'll copy the pointer to a local variable, thr_kbpdata,
+	 * and we must prevent the compiler from aliasing the two
+	 * pointers.  Only a compiler barrier is required, not a full
+	 * memory barrier, because everything takes place on a single CPU.
+	 */
+ restart:
+	thr_kbpdata = chbi->cur_kbpdata;
+	barrier();
+
+	/* Normally we can keep the same debug register settings as the
+	 * last time this task ran.  But if the kernel breakpoints have
+	 * changed or any user breakpoints have been registered or
+	 * unregistered, we need to handle the updates and possibly
+	 * send out some notifications.
+	 */
+	if (unlikely(thbi->gennum != thr_kbpdata->gennum)) {
+		struct hw_breakpoint *bp;
+		int i;
+		int num;
+
+		thbi->gennum = thr_kbpdata->gennum;
+		arch_update_thbi(thbi, thr_kbpdata);
+		num = thr_kbpdata->num_kbps;
+
+		/* This code can be invoked while a debugger is actively
+		 * updating the thread's breakpoint list. We use RCU to
+		 * protect our access to the list pointers. */
+		thbi->num_installed = 0;
+		i = HB_NUM;
+		list_for_each_entry_rcu(bp, &thbi->thread_bps, node) {
+
+			/* If this register is allocated for kernel bps,
+			 * don't install.  Otherwise do. */
+			if (--i < num) {
+				if (bp->status == HW_BREAKPOINT_INSTALLED) {
+					if (bp->uninstalled)
+						(bp->uninstalled)(bp);
+					bp->status = HW_BREAKPOINT_REGISTERED;
+				}
+			} else {
+				++thbi->num_installed;
+				if (bp->status != HW_BREAKPOINT_INSTALLED) {
+					bp->status = HW_BREAKPOINT_INSTALLED;
+					if (bp->installed)
+						(bp->installed)(bp);
+				}
+			}
+		}
+	}
+
+	/* Set the debug register */
+	arch_install_thbi(thbi);
+
+	/* Were there any kernel breakpoint changes while we were running? */
+	if (unlikely(chbi->cur_kbpdata != thr_kbpdata)) {
+
+		/* Some debug registers now be assigned to kernel bps and
+		 * we might have messed them up.  Reload all the kernel bps
+		 * and then reload the thread bps.
+		 */
+		arch_install_chbi(chbi);
+		goto restart;
+	}
+
+	rcu_read_unlock();
+	put_cpu_no_resched();
+}
+
+/*
+ * Install the debug register values for just the kernel, no thread.
+ */
+static void switch_to_none_hw_breakpoint(void)
+{
+	struct cpu_hw_breakpoint *chbi;
+
+	chbi = &per_cpu(cpu_info, get_cpu());
+	chbi->bp_task = NULL;
+
+	/* This routine gets called from only two places.  In one
+	 * the caller holds the hw_breakpoint_mutex; in the other
+	 * interrupts are disabled.  In either case, no kernel
+	 * breakpoint updates can arrive while the routine runs.
+	 * So we don't need to use RCU.
+	 */
+	arch_install_none(chbi);
+	put_cpu_no_resched();
+}
+
+/*
+ * Update the debug registers on this CPU.
+ */
+static void update_this_cpu(void *unused)
+{
+	struct cpu_hw_breakpoint *chbi;
+	struct task_struct *tsk = current;
+
+	chbi = &per_cpu(cpu_info, get_cpu());
+
+	/* Install both the kernel and the user breakpoints */
+	arch_install_chbi(chbi);
+	if (test_tsk_thread_flag(tsk, TIF_DEBUG))
+		switch_to_thread_hw_breakpoint(tsk);
+
+	put_cpu_no_resched();
+}
+
+/*
+ * Tell all CPUs to update their debug registers.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void update_all_cpus(void)
+{
+	/* We don't need to use any sort of memory barrier.  The IPI
+	 * carried out by on_each_cpu() includes its own barriers.
+	 */
+	on_each_cpu(update_this_cpu, NULL, 0);
+	synchronize_rcu();
+}
+
+/*
+ * Load the debug registers during startup of a CPU.
+ */
+void load_debug_registers(void)
+{
+	unsigned long flags;
+
+	/* Prevent IPIs for new kernel breakpoint updates */
+	local_irq_save(flags);
+
+	rcu_read_lock();
+	update_this_cpu(NULL);
+	rcu_read_unlock();
+
+	local_irq_restore(flags);
+}
+
+/*
+ * Take the 4 highest-priority breakpoints in a thread and accumulate
+ * their priorities in tprio.  Highest-priority entry is in tprio[3].
+ */
+static void accum_thread_tprio(struct thread_hw_breakpoint *thbi)
+{
+	int i;
+
+	for (i = HB_NUM - 1; i >= 0 && thbi->bps[i]; --i)
+		tprio[i] = max(tprio[i], thbi->bps[i]->priority);
+}
+
+/*
+ * Recalculate the value of the tprio array, the maximum priority levels
+ * requested by user breakpoints in all threads.
+ *
+ * Each thread has a list of registered breakpoints, kept in order of
+ * decreasing priority.  We'll set tprio[0] to the maximum priority of
+ * the first entries in all the lists, tprio[1] to the maximum priority
+ * of the second entries in all the lists, etc.  In the end, we'll know
+ * that no thread requires breakpoints with priorities higher than the
+ * values in tprio.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void recalc_tprio(void)
+{
+	struct thread_hw_breakpoint *thbi;
+
+	memset(tprio, 0, sizeof tprio);
+
+	/* Loop through all threads having registered breakpoints
+	 * and accumulate the maximum priority levels in tprio.
+	 */
+	list_for_each_entry(thbi, &thread_list, node)
+		accum_thread_tprio(thbi);
+}
+
+/*
+ * Decide how many debug registers will be allocated to kernel breakpoints
+ * and consequently, how many remain available for user breakpoints.
+ *
+ * The priorities of the entries in the list of registered kernel bps
+ * are compared against the priorities stored in tprio[].  The 4 highest
+ * winners overall get to be installed in a debug register; num_kpbs
+ * keeps track of how many of those winners come from the kernel list.
+ *
+ * If num_kbps changes, or if a kernel bp changes its installation status,
+ * then call update_all_cpus() so that the debug registers will be set
+ * correctly on every CPU.  If neither condition holds then the set of
+ * kernel bps hasn't changed, and nothing more needs to be done.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void balance_kernel_vs_user(void)
+{
+	int k, u;
+	int changed = 0;
+	struct hw_breakpoint *bp;
+	struct kernel_bp_data *new_kbpdata;
+
+	/* Determine how many debug registers are available for kernel
+	 * breakpoints as opposed to user breakpoints, based on the
+	 * priorities.  Ties are resolved in favor of user bps.
+	 */
+	k = 0;			/* Next kernel bp to allocate */
+	u = HB_NUM - 1;		/* Next user bp to allocate */
+	bp = list_entry(kernel_bps.next, struct hw_breakpoint, node);
+	while (k <= u) {
+		if (&bp->node == &kernel_bps || tprio[u] >= bp->priority)
+			--u;		/* User bps win a slot */
+		else {
+			++k;		/* Kernel bp wins a slot */
+			if (bp->status != HW_BREAKPOINT_INSTALLED)
+				changed = 1;
+			bp = list_entry(bp->node.next, struct hw_breakpoint,
+					node);
+		}
+	}
+	if (k != cur_kbpdata->num_kbps)
+		changed = 1;
+
+	/* Notify the remaining kernel breakpoints that they are about
+	 * to be uninstalled.
+	 */
+	list_for_each_entry_from(bp, &kernel_bps, node) {
+		if (bp->status == HW_BREAKPOINT_INSTALLED) {
+			if (bp->uninstalled)
+				(bp->uninstalled)(bp);
+			bp->status = HW_BREAKPOINT_REGISTERED;
+			changed = 1;
+		}
+	}
+
+	if (changed) {
+		cur_kbpindex ^= 1;
+		new_kbpdata = &kbpdata[cur_kbpindex];
+		new_kbpdata->gennum = cur_kbpdata->gennum + 1;
+		new_kbpdata->num_kbps = k;
+		arch_new_kbpdata(new_kbpdata);
+		u = 0;
+		list_for_each_entry(bp, &kernel_bps, node) {
+			if (u >= k)
+				break;
+			new_kbpdata->bps[u] = bp;
+			++u;
+		}
+		rcu_assign_pointer(cur_kbpdata, new_kbpdata);
+
+		/* Tell all the CPUs to update their debug registers */
+		update_all_cpus();
+
+		/* Notify the breakpoints that just got installed */
+		for (u = 0; u < k; ++u) {
+			bp = new_kbpdata->bps[u];
+			if (bp->status != HW_BREAKPOINT_INSTALLED) {
+				bp->status = HW_BREAKPOINT_INSTALLED;
+				if (bp->installed)
+					(bp->installed)(bp);
+			}
+		}
+	}
+}
+
+/*
+ * Return the pointer to a thread's hw_breakpoint info area,
+ * and try to allocate one if it doesn't exist.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static struct thread_hw_breakpoint *alloc_thread_hw_breakpoint(
+		struct task_struct *tsk)
+{
+	if (!tsk->thread.hw_breakpoint_info && !(tsk->flags & PF_EXITING)) {
+		struct thread_hw_breakpoint *thbi;
+
+		thbi = kzalloc(sizeof(struct thread_hw_breakpoint),
+				GFP_KERNEL);
+		if (thbi) {
+			INIT_LIST_HEAD(&thbi->node);
+			INIT_LIST_HEAD(&thbi->thread_bps);
+
+			/* Force an update the next time tsk runs */
+			thbi->gennum = cur_kbpdata->gennum - 2;
+			tsk->thread.hw_breakpoint_info = thbi;
+		}
+	}
+	return tsk->thread.hw_breakpoint_info;
+}
+
+/*
+ * Erase all the hardware breakpoint info associated with a thread.
+ *
+ * If tsk != current then tsk must not be usable (for example, a
+ * child being cleaned up from a failed fork).
+ */
+void flush_thread_hw_breakpoint(struct task_struct *tsk)
+{
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	struct hw_breakpoint *bp;
+
+	if (!thbi)
+		return;
+	mutex_lock(&hw_breakpoint_mutex);
+
+	/* Let the breakpoints know they are being uninstalled */
+	list_for_each_entry(bp, &thbi->thread_bps, node) {
+		if (bp->status == HW_BREAKPOINT_INSTALLED && bp->uninstalled)
+			(bp->uninstalled)(bp);
+		bp->status = 0;
+	}
+
+	/* Remove tsk from the list of all threads with registered bps */
+	list_del(&thbi->node);
+
+	/* The thread no longer has any breakpoints associated with it */
+	clear_tsk_thread_flag(tsk, TIF_DEBUG);
+	tsk->thread.hw_breakpoint_info = NULL;
+	kfree(thbi);
+
+	/* Recalculate and rebalance the kernel-vs-user priorities */
+	recalc_tprio();
+	balance_kernel_vs_user();
+
+	/* Actually uninstall the breakpoints if necessary */
+	if (tsk == current)
+		switch_to_none_hw_breakpoint();
+	mutex_unlock(&hw_breakpoint_mutex);
+}
+
+/*
+ * Copy the hardware breakpoint info from a thread to its cloned child.
+ */
+int copy_thread_hw_breakpoint(struct task_struct *tsk,
+		struct task_struct *child, unsigned long clone_flags)
+{
+	/* We will assume that breakpoint settings are not inherited
+	 * and the child starts out with no debug registers set.
+	 * But what about CLONE_PTRACE?
+	 */
+	clear_tsk_thread_flag(child, TIF_DEBUG);
+	return 0;
+}
+
+/*
+ * Store the highest-priority thread breakpoint entries in an array.
+ */
+static void store_thread_bp_array(struct thread_hw_breakpoint *thbi)
+{
+	struct hw_breakpoint *bp;
+	int i;
+
+	i = HB_NUM - 1;
+	list_for_each_entry(bp, &thbi->thread_bps, node) {
+		thbi->bps[i] = bp;
+		arch_store_thread_bp_array(thbi, bp, i);
+		if (--i < 0)
+			break;
+	}
+	while (i >= 0)
+		thbi->bps[i--] = NULL;
+
+	/* Force an update the next time this task runs */
+	thbi->gennum = cur_kbpdata->gennum - 2;
+}
+
+/*
+ * Insert a new breakpoint in a priority-sorted list.
+ * Return the bp's index in the list.
+ *
+ * Thread invariants:
+ *	tsk_thread_flag(tsk, TIF_DEBUG) set implies
+ *		tsk->thread.hw_breakpoint_info is not NULL.
+ *	tsk_thread_flag(tsk, TIF_DEBUG) set iff thbi->thread_bps is non-empty
+ *		iff thbi->node is on thread_list.
+ */
+static int insert_bp_in_list(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi, struct task_struct *tsk)
+{
+	struct list_head *head;
+	int pos;
+	struct hw_breakpoint *temp_bp;
+
+	/* tsk and thbi are NULL for kernel bps, non-NULL for user bps */
+	if (tsk)
+		head = &thbi->thread_bps;
+	else
+		head = &kernel_bps;
+
+	/* Equal-priority breakpoints get listed first-come-first-served */
+	pos = 0;
+	list_for_each_entry(temp_bp, head, node) {
+		if (bp->priority > temp_bp->priority)
+			break;
+		++pos;
+	}
+	bp->status = HW_BREAKPOINT_REGISTERED;
+	list_add_tail(&bp->node, &temp_bp->node);
+
+	if (tsk) {
+		store_thread_bp_array(thbi);
+
+		/* Is this the thread's first registered breakpoint? */
+		if (list_empty(&thbi->node)) {
+			set_tsk_thread_flag(tsk, TIF_DEBUG);
+			list_add(&thbi->node, &thread_list);
+		}
+	}
+	return pos;
+}
+
+/*
+ * Remove a breakpoint from its priority-sorted list.
+ *
+ * See the invariants mentioned above.
+ */
+static void remove_bp_from_list(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi, struct task_struct *tsk)
+{
+	/* Remove bp from the thread's/kernel's list.  If the list is now
+	 * empty we must clear the TIF_DEBUG flag.  But keep the
+	 * thread_hw_breakpoint structure, so that the virtualized debug
+	 * register values will remain valid.
+	 */
+	list_del(&bp->node);
+	if (tsk) {
+		store_thread_bp_array(thbi);
+
+		if (list_empty(&thbi->thread_bps)) {
+			list_del_init(&thbi->node);
+			clear_tsk_thread_flag(tsk, TIF_DEBUG);
+		}
+	}
+
+	/* Tell the breakpoint it is being uninstalled */
+	if (bp->status == HW_BREAKPOINT_INSTALLED && bp->uninstalled)
+		(bp->uninstalled)(bp);
+	bp->status = 0;
+}
+
+/*
+ * Validate the settings in a hw_breakpoint structure.
+ */
+static int validate_settings(struct hw_breakpoint *bp, struct task_struct *tsk,
+		unsigned long address, unsigned len, unsigned int type)
+{
+	int ret;
+	unsigned int align;
+
+	ret = arch_validate_hwbkpt_settings(bp, address, len, type, &align);
+	if (ret < 0)
+		goto err;
+
+	/* Check that the low-order bits of the address are appropriate
+	 * for the alignment implied by len.
+	 */
+	if (address & align)
+		return -EINVAL;
+
+	/* Check that the virtual address is in the proper range */
+	if (tsk) {
+		if (!arch_check_va_in_userspace(address, tsk))
+			return -EFAULT;
+	} else {
+		if (!arch_check_va_in_kernelspace(address))
+			return -EFAULT;
+	}
+ err:
+	return ret;
+}
+
+/*
+ * Actual implementation of register_user_hw_breakpoint.
+ */
+static int __register_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp,
+		unsigned long address, unsigned len, unsigned type)
+{
+	int rc;
+	struct thread_hw_breakpoint *thbi;
+	int pos;
+
+	bp->status = 0;
+	rc = validate_settings(bp, tsk, address, len, type);
+	if (rc)
+		return rc;
+
+	thbi = alloc_thread_hw_breakpoint(tsk);
+	if (!thbi)
+		return -ENOMEM;
+
+	/* Insert bp in the thread's list */
+	pos = insert_bp_in_list(bp, thbi, tsk);
+	arch_register_user_hw_breakpoint(bp, thbi);
+
+	/* Update and rebalance the priorities.  We don't need to go through
+	 * the list of all threads; adding a breakpoint can only cause the
+	 * priorities for this thread to increase.
+	 */
+	accum_thread_tprio(thbi);
+	balance_kernel_vs_user();
+
+	/* Did bp get allocated to a debug register?  We can tell from its
+	 * position in the list.  The number of registers allocated to
+	 * kernel breakpoints is num_kbps; all the others are available for
+	 * user breakpoints.  If bp's position in the priority-ordered list
+	 * is low enough, it will get a register.
+	 */
+	if (pos < HB_NUM - cur_kbpdata->num_kbps) {
+		rc = 1;
+
+		/* Does it need to be installed right now? */
+		if (tsk == current)
+			switch_to_thread_hw_breakpoint(tsk);
+		/* Otherwise it will get installed the next time tsk runs */
+	}
+
+	return rc;
+}
+
+/**
+ * register_user_hw_breakpoint - register a hardware breakpoint for user space
+ * @tsk: the task in whose memory space the breakpoint will be set
+ * @bp: the breakpoint structure to register
+ * @address: location (virtual address) of the breakpoint
+ * @len: encoded extent of the breakpoint address (1, 2, 4, or 8 bytes)
+ * @type: breakpoint type (read-only, write-only, read-write, or execute)
+ *
+ * This routine registers a breakpoint to be associated with @tsk's
+ * memory space and active only while @tsk is running.  It does not
+ * guarantee that the breakpoint will be allocated to a debug register
+ * immediately; there may be other higher-priority breakpoints registered
+ * which require the use of all the debug registers.
+ *
+ * @tsk will normally be a process being debugged by the current process,
+ * but it may also be the current process.
+ *
+ * @address, @len, and @type are checked for validity and stored in
+ * encoded form in @bp.  @bp->triggered and @bp->priority must be set
+ * properly.
+ *
+ * Returns 1 if @bp is allocated to a debug register, 0 if @bp is
+ * registered but not allowed to be installed, otherwise a negative error
+ * code.
+ */
+int register_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp,
+		const void __user *address, unsigned len, unsigned type)
+{
+	int rc;
+
+	mutex_lock(&hw_breakpoint_mutex);
+	rc = __register_user_hw_breakpoint(tsk, bp,
+			(unsigned long) address, len, type);
+	mutex_unlock(&hw_breakpoint_mutex);
+	return rc;
+}
+
+/*
+ * Actual implementation of unregister_user_hw_breakpoint.
+ */
+static void __unregister_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp)
+{
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+
+	if (!bp->status)
+		return;		/* Not registered */
+
+	/* Remove bp from the thread's list */
+	remove_bp_from_list(bp, thbi, tsk);
+	arch_unregister_user_hw_breakpoint(bp, thbi);
+
+	/* Recalculate and rebalance the kernel-vs-user priorities,
+	 * and actually uninstall bp if necessary.
+	 */
+	recalc_tprio();
+	balance_kernel_vs_user();
+	if (tsk == current)
+		switch_to_thread_hw_breakpoint(tsk);
+}
+
+/**
+ * unregister_user_hw_breakpoint - unregister a hardware breakpoint for user space
+ * @tsk: the task in whose memory space the breakpoint is registered
+ * @bp: the breakpoint structure to unregister
+ *
+ * Uninstalls and unregisters @bp.
+ */
+void unregister_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp)
+{
+	mutex_lock(&hw_breakpoint_mutex);
+	__unregister_user_hw_breakpoint(tsk, bp);
+	mutex_unlock(&hw_breakpoint_mutex);
+}
+
+/**
+ * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
+ * @bp: the breakpoint structure to register
+ * @address: location (virtual address) of the breakpoint
+ * @len: encoded extent of the breakpoint address (1, 2, 4, or 8 bytes)
+ * @type: breakpoint type (read-only, write-only, read-write, or execute)
+ *
+ * This routine registers a breakpoint to be active at all times.  It
+ * does not guarantee that the breakpoint will be allocated to a debug
+ * register immediately; there may be other higher-priority breakpoints
+ * registered which require the use of all the debug registers.
+ *
+ * @address, @len, and @type are checked for validity and stored in
+ * encoded form in @bp.  @bp->triggered and @bp->priority must be set
+ * properly.
+ *
+ * Returns 1 if @bp is allocated to a debug register, 0 if @bp is
+ * registered but not allowed to be installed, otherwise a negative error
+ * code.
+ */
+int register_kernel_hw_breakpoint(struct hw_breakpoint *bp,
+		const void *address, unsigned len, unsigned type)
+{
+	int rc;
+	int pos;
+
+	bp->status = 0;
+	rc = validate_settings(bp, NULL, (unsigned long) address, len, type);
+	if (rc)
+		return rc;
+
+	mutex_lock(&hw_breakpoint_mutex);
+
+	/* Insert bp in the kernel's list */
+	pos = insert_bp_in_list(bp, NULL, NULL);
+	arch_register_kernel_hw_breakpoint(bp);
+
+	/* Rebalance the priorities.  This will install bp if it
+	 * was allocated a debug register.
+	 */
+	balance_kernel_vs_user();
+
+	/* Did bp get allocated to a debug register?  We can tell from its
+	 * position in the list.  The number of registers allocated to
+	 * kernel breakpoints is num_kbps; all the others are available for
+	 * user breakpoints.  If bp's position in the priority-ordered list
+	 * is low enough, it will get a register.
+	 */
+	if (pos < cur_kbpdata->num_kbps)
+		rc = 1;
+
+	mutex_unlock(&hw_breakpoint_mutex);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
+
+/**
+ * unregister_kernel_hw_breakpoint - unregister a hardware breakpoint for kernel space
+ * @bp: the breakpoint structure to unregister
+ *
+ * Uninstalls and unregisters @bp.
+ */
+void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp)
+{
+	if (!bp->status)
+		return;		/* Not registered */
+	mutex_lock(&hw_breakpoint_mutex);
+
+	/* Remove bp from the kernel's list */
+	remove_bp_from_list(bp, NULL, NULL);
+	arch_unregister_kernel_hw_breakpoint(bp);
+
+	/* Rebalance the priorities.  This will uninstall bp if it
+	 * was allocated a debug register.
+	 */
+	balance_kernel_vs_user();
+
+	mutex_unlock(&hw_breakpoint_mutex);
+}
+EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);

Re: [RFC Patch 1/9] Introducing generic hardware breakpoint handler interfaces

[Alan Stern]

On Tue, 7 Oct 2008, K.Prasad wrote:

> This patch introduces two new files hw_breakpoint.[ch] which defines the 
> generic interfaces to use hardware breakpoint infrastructure of the system. 

...
> --- /dev/null
> +++ linux-bkpt-lkml-27-rc9/include/asm-generic/hw_breakpoint.h
> @@ -0,0 +1,236 @@
> +#ifndef	_ASM_GENERIC_HW_BREAKPOINT_H
> +#define	_ASM_GENERIC_HW_BREAKPOINT_H
> +
> +#ifndef __ARCH_HW_BREAKPOINT_H
> +#error "Please don't include this file directly"
> +#endif
> +
> +#ifdef	__KERNEL__
> +#include <linux/list.h>
> +#include <linux/types.h>
> +
> +/**
> + * struct hw_breakpoint - unified kernel/user-space hardware breakpoint
> + * @node: internal linked-list management
> + * @triggered: callback invoked when the breakpoint is hit

The kerneldoc needs to be updated to match the structure.  @triggered
doesn't exist any more; instead there are @pre_handler and
@post_handler.

...
> + * When a breakpoint gets hit, the @triggered callback is invoked
> + * in_interrupt with a pointer to the %hw_breakpoint structure and the
> + * processor registers.  Execute-breakpoint traps occur before the
> + * breakpointed instruction runs; when the callback returns the
> + * instruction is restarted (this time without a debug exception).  All
> + * other types of trap occur after the memory access has taken place.
> + * Breakpoints are disabled while @triggered runs, to avoid recursive
> + * traps and allow unhindered access to breakpointed memory.

This paragraph needs to be fixed as well.

...
> +/*
> + * The following routines help the user determine if the architecture supports
> + * a trigger-before access/execution mechanism or a trigger-after
> + * access/execution. This is dependent on the type of breakpoint and the
> + * architecture
> + */
> +int trigger_before_arch(unsigned type);
> +int trigger_after_arch(unsigned type);

These routines should have hwbp_ in their name (or something similar).  
And they don't need to have _arch.

Alan Stern

Re: [RFC Patch 1/9] Introducing generic hardware breakpoint handler interfaces

[K.Prasad]

On Tue, Oct 07, 2008 at 11:21:53AM -0400, Alan Stern wrote:
> On Tue, 7 Oct 2008, K.Prasad wrote:
> 
> > This patch introduces two new files hw_breakpoint.[ch] which defines the 
> > generic interfaces to use hardware breakpoint infrastructure of the system. 
> 
> ...
> > --- /dev/null
> > +++ linux-bkpt-lkml-27-rc9/include/asm-generic/hw_breakpoint.h
> > @@ -0,0 +1,236 @@
> > +#ifndef	_ASM_GENERIC_HW_BREAKPOINT_H
> > +#define	_ASM_GENERIC_HW_BREAKPOINT_H
> > +
> > +#ifndef __ARCH_HW_BREAKPOINT_H
> > +#error "Please don't include this file directly"
> > +#endif
> > +
> > +#ifdef	__KERNEL__
> > +#include <linux/list.h>
> > +#include <linux/types.h>
> > +
> > +/**
> > + * struct hw_breakpoint - unified kernel/user-space hardware breakpoint
> > + * @node: internal linked-list management
> > + * @triggered: callback invoked when the breakpoint is hit
> 
> The kerneldoc needs to be updated to match the structure.  @triggered
> doesn't exist any more; instead there are @pre_handler and
> @post_handler.
> 
> ...
> > + * When a breakpoint gets hit, the @triggered callback is invoked
> > + * in_interrupt with a pointer to the %hw_breakpoint structure and the
> > + * processor registers.  Execute-breakpoint traps occur before the
> > + * breakpointed instruction runs; when the callback returns the
> > + * instruction is restarted (this time without a debug exception).  All
> > + * other types of trap occur after the memory access has taken place.
> > + * Breakpoints are disabled while @triggered runs, to avoid recursive
> > + * traps and allow unhindered access to breakpointed memory.
> 
> This paragraph needs to be fixed as well.
> 
> ...
> > +/*
> > + * The following routines help the user determine if the architecture supports
> > + * a trigger-before access/execution mechanism or a trigger-after
> > + * access/execution. This is dependent on the type of breakpoint and the
> > + * architecture
> > + */
> > +int trigger_before_arch(unsigned type);
> > +int trigger_after_arch(unsigned type);
> 
> These routines should have hwbp_ in their name (or something similar).  
> And they don't need to have _arch.
> 
> Alan Stern
>
I agree this part of the patch needs cleanup. Will do so during the next
iteration of the patchset. trigger_<before/after>_arch() routines are
rendered redundant through the pre_ and post_handler_allowed() routines
and I will remove the above two lines too.

Thanks,
K.Prasad
 

[RFC Patch 2/9] x86 architecture implementation of Hardware Breakpoint interfaces

[K.Prasad]

This patch introduces two new files named hw_breakpoint.[ch] inside x86 specific
directories. They contain functions which help validate and serve requests for 
using Hardware Breakpoint registers on x86 processors.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/Makefile        |    2 
 arch/x86/kernel/hw_breakpoint.c |  684 ++++++++++++++++++++++++++++++++++++++++
 include/asm-x86/hw_breakpoint.h |  121 +++++++
 3 files changed, 806 insertions(+), 1 deletion(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/hw_breakpoint.c
@@ -0,0 +1,684 @@
+/*
+ * 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 (C) 2007 Alan Stern
+ * Copyright (C) 2008 IBM Corporation
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#include <linux/init.h>
+#include <linux/irqflags.h>
+#include <linux/kdebug.h>
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/rculist.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/percpu.h>
+
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+
+DEFINE_PER_CPU(unsigned int, sstep_reason) = 0;
+
+/* Arch-specific hook routines */
+
+/*
+ * Install the kernel breakpoints in their debug registers.
+ */
+static void arch_install_chbi(struct cpu_hw_breakpoint *chbi)
+{
+	struct hw_breakpoint **bps;
+
+	/* Don't allow debug exceptions while we update the registers */
+	set_debugreg(0UL, 7);
+	chbi->cur_kbpdata = rcu_dereference(cur_kbpdata);
+
+	/* Kernel breakpoints are stored starting in DR0 and going up */
+	bps = chbi->cur_kbpdata->bps;
+	switch (chbi->cur_kbpdata->num_kbps) {
+	case 4:
+		set_debugreg(bps[3]->info.address, 3);
+	case 3:
+		set_debugreg(bps[2]->info.address, 2);
+	case 2:
+		set_debugreg(bps[1]->info.address, 1);
+	case 1:
+		set_debugreg(bps[0]->info.address, 0);
+	}
+	/* No need to set DR6 */
+	set_debugreg(chbi->cur_kbpdata->mkdr7, 7);
+}
+
+/*
+ * Update an out-of-date thread hw_breakpoint info structure.
+ */
+static void arch_update_thbi(struct thread_hw_breakpoint *thbi,
+		struct kernel_bp_data *thr_kbpdata)
+{
+	int num = thr_kbpdata->num_kbps;
+
+	thbi->tkdr7 = thr_kbpdata->mkdr7 | (thbi->tdr7 & ~kdr7_masks[num]);
+}
+
+/*
+ * Install the thread breakpoints in their debug registers.
+ */
+static void arch_install_thbi(struct thread_hw_breakpoint *thbi)
+{
+	/* Install the user breakpoints.  Kernel breakpoints are stored
+	 * starting in DR0 and going up; there are num_kbps of them.
+	 * User breakpoints are stored starting in DR3 and going down,
+	 * as many as we have room for.
+	 */
+	switch (thbi->num_installed) {
+	case 4:
+		set_debugreg(thbi->tdr[0], 0);
+	case 3:
+		set_debugreg(thbi->tdr[1], 1);
+	case 2:
+		set_debugreg(thbi->tdr[2], 2);
+	case 1:
+		set_debugreg(thbi->tdr[3], 3);
+	}
+	/* No need to set DR6 */
+	set_debugreg(thbi->tkdr7, 7);
+}
+
+/*
+ * Install the debug register values for just the kernel, no thread.
+ */
+static void arch_install_none(struct cpu_hw_breakpoint *chbi)
+{
+	set_debugreg(chbi->cur_kbpdata->mkdr7, 7);
+}
+
+/*
+ * Create a new kbpdata entry.
+ */
+static void arch_new_kbpdata(struct kernel_bp_data *new_kbpdata)
+{
+	int num = new_kbpdata->num_kbps;
+
+	new_kbpdata->mkdr7 = kdr7 & (kdr7_masks[num] | DR_GLOBAL_SLOWDOWN);
+}
+
+/*
+ * Store a thread breakpoint array entry's address
+ */
+static void arch_store_thread_bp_array(struct thread_hw_breakpoint *thbi,
+		struct hw_breakpoint *bp, int i)
+{
+	thbi->tdr[i] = bp->info.address;
+}
+
+int pre_handler_allowed(unsigned type)
+{
+	if (type == HW_BREAKPOINT_EXECUTE)
+		return 1;
+	else
+		return -EINVAL;
+}
+
+int post_handler_allowed(unsigned type)
+{
+	/* We can have a post handler for all types of breakpoints */
+	return 1;
+}
+
+/*
+ * Store a breakpoint's encoded address, length, and type.
+ */
+static void arch_store_info(struct hw_breakpoint *bp,
+		unsigned long address, unsigned len, unsigned type)
+{
+	bp->info.address = address;
+	bp->info.len = len;
+	bp->info.type = type;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
+			unsigned long address, unsigned len, unsigned int type,
+			unsigned int *align)
+{
+	int ret = -EINVAL;
+
+	switch (type) {
+	case HW_BREAKPOINT_EXECUTE:
+		if (len != HW_BREAKPOINT_LEN_EXECUTE)
+			return ret;
+		break;
+	case HW_BREAKPOINT_WRITE:
+				break;
+	case HW_BREAKPOINT_IO:
+				break;
+	case HW_BREAKPOINT_RW:
+				break;
+	default:
+		return ret;
+	}
+
+	switch (len) {
+	case HW_BREAKPOINT_LEN_1:
+		*align = 0;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		*align = 1;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		*align = 3;
+		break;
+	default:
+		return ret;
+	}
+
+	if ((pre_handler_allowed(type) && (bp->pre_handler)) ||
+		(post_handler_allowed(type) && (bp->post_handler))) {
+		ret = 0;
+		arch_store_info(bp, address, len, type);
+	}
+	return ret;
+}
+
+/*
+ * Check for virtual address in user space.
+ */
+static int arch_check_va_in_userspace(unsigned long va,
+		struct task_struct *tsk)
+{
+#ifndef	CONFIG_X86_64
+#define	TASK_SIZE_OF(t)	TASK_SIZE
+#endif
+	return (va < TASK_SIZE_OF(tsk));
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+static int arch_check_va_in_kernelspace(unsigned long va)
+{
+#ifndef	CONFIG_X86_64
+#define	TASK_SIZE64	TASK_SIZE
+#endif
+	return (va >= TASK_SIZE64);
+}
+
+/*
+ * Encode the length, type, Exact, and Enable bits for a particular breakpoint
+ * as stored in debug register 7.
+ */
+static unsigned long encode_dr7(int drnum, unsigned len, unsigned type)
+{
+	unsigned long temp;
+
+	temp = (len | type) & 0xf;
+	temp <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
+	temp |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)) |
+				DR_GLOBAL_SLOWDOWN;
+	return temp;
+}
+
+/*
+ * Calculate the DR7 value for a list of kernel or user breakpoints.
+ */
+static unsigned long calculate_dr7(struct thread_hw_breakpoint *thbi)
+{
+	int is_user;
+	struct list_head *bp_list;
+	struct hw_breakpoint *bp;
+	int i;
+	int drnum;
+	unsigned long dr7;
+
+	if (thbi) {
+		is_user = 1;
+		bp_list = &thbi->thread_bps;
+		drnum = HB_NUM - 1;
+	} else {
+		is_user = 0;
+		bp_list = &kernel_bps;
+		drnum = 0;
+	}
+
+	/* Kernel bps are assigned from DR0 on up, and user bps are assigned
+	 * from DR3 on down.  Accumulate all 4 bps; the kernel DR7 mask will
+	 * select the appropriate bits later.
+	 */
+	dr7 = 0;
+	i = 0;
+	list_for_each_entry(bp, bp_list, node) {
+
+		/* Get the debug register number and accumulate the bits */
+		dr7 |= encode_dr7(drnum, bp->info.len, bp->info.type);
+		if (++i >= HB_NUM)
+			break;
+		if (is_user)
+			--drnum;
+		else
+			++drnum;
+	}
+	return dr7;
+}
+
+/*
+ * Register a new user breakpoint structure.
+ */
+static void arch_register_user_hw_breakpoint(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi)
+{
+	thbi->tdr7 = calculate_dr7(thbi);
+
+	/* If this is an execution breakpoint for the current PC address,
+	 * we should clear the task's RF so that the bp will be certain
+	 * to trigger.
+	 *
+	 * FIXME: It's not so easy to get hold of the task's PC as a linear
+	 * address!  ptrace.c does this already...
+	 */
+}
+
+/*
+ * Unregister a user breakpoint structure.
+ */
+static void arch_unregister_user_hw_breakpoint(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi)
+{
+	thbi->tdr7 = calculate_dr7(thbi);
+}
+
+/*
+ * Register a kernel breakpoint structure.
+ */
+static void arch_register_kernel_hw_breakpoint(
+		struct hw_breakpoint *bp)
+{
+	kdr7 = calculate_dr7(NULL);
+}
+
+/*
+ * Unregister a kernel breakpoint structure.
+ */
+static void arch_unregister_kernel_hw_breakpoint(
+		struct hw_breakpoint *bp)
+{
+	kdr7 = calculate_dr7(NULL);
+}
+
+
+/* End of arch-specific hook routines */
+
+
+/*
+ * Copy out the debug register information for a core dump.
+ *
+ * tsk must be equal to current.
+ */
+void dump_thread_hw_breakpoint(struct task_struct *tsk, int u_debugreg[8])
+{
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	int i;
+
+	memset(u_debugreg, 0, sizeof u_debugreg);
+	if (thbi) {
+		for (i = 0; i < HB_NUM; ++i)
+			u_debugreg[i] = thbi->vdr_bps[i].info.address;
+		u_debugreg[7] = thbi->vdr7;
+	}
+	u_debugreg[6] = tsk->thread.vdr6;
+}
+
+/*
+ * Ptrace support: breakpoint trigger routine.
+ */
+
+static struct thread_hw_breakpoint *alloc_thread_hw_breakpoint(
+		struct task_struct *tsk);
+static int __register_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp,
+		unsigned long address, unsigned len, unsigned type);
+static void __unregister_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp);
+
+static void ptrace_triggered(struct hw_breakpoint *bp, struct pt_regs *regs)
+{
+	struct task_struct *tsk = current;
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	int i;
+
+	/* Store in the virtual DR6 register the fact that the breakpoint
+	 * was hit so the thread's debugger will see it.
+	 */
+	if (thbi) {
+		i = bp - thbi->vdr_bps;
+		tsk->thread.vdr6 |= (DR_TRAP0 << i);
+	}
+}
+
+/*
+ * Handle PTRACE_PEEKUSR calls for the debug register area.
+ */
+unsigned long thread_get_debugreg(struct task_struct *tsk, int n)
+{
+	struct thread_hw_breakpoint *thbi;
+	unsigned long val = 0;
+
+	mutex_lock(&hw_breakpoint_mutex);
+	thbi = tsk->thread.hw_breakpoint_info;
+	if (n < HB_NUM) {
+		if (thbi)
+			val = thbi->vdr_bps[n].info.address;
+	} else if (n == 6) {
+		val = tsk->thread.vdr6;
+	} else if (n == 7) {
+		if (thbi)
+			val = thbi->vdr7;
+	}
+	mutex_unlock(&hw_breakpoint_mutex);
+	return val;
+}
+
+/*
+ * Decode the length and type bits for a particular breakpoint as
+ * stored in debug register 7.  Return the "enabled" status.
+ */
+static int decode_dr7(unsigned long dr7, int bpnum, unsigned *len,
+		unsigned *type)
+{
+	int temp = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
+
+	*len = (temp & 0xc) | 0x40;
+	*type = (temp & 0x3) | 0x80;
+	return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
+}
+
+/*
+ * Handle ptrace writes to debug register 7.
+ */
+static int ptrace_write_dr7(struct task_struct *tsk,
+		struct thread_hw_breakpoint *thbi, unsigned long data)
+{
+	struct hw_breakpoint *bp;
+	int i;
+	int rc = 0;
+	unsigned long old_dr7 = thbi->vdr7;
+
+	data &= ~DR_CONTROL_RESERVED;
+
+	/* Loop through all the hardware breakpoints, making the
+	 * appropriate changes to each.
+	 */
+ restore_settings:
+	thbi->vdr7 = data;
+	bp = &thbi->vdr_bps[0];
+	for (i = 0; i < HB_NUM; (++i, ++bp)) {
+		int enabled;
+		unsigned len, type;
+
+		enabled = decode_dr7(data, i, &len, &type);
+
+		/* Unregister the breakpoint before trying to change it */
+		if (bp->status)
+			__unregister_user_hw_breakpoint(tsk, bp);
+
+		/* Now register the breakpoint if it should be enabled.
+		 * New invalid entries will raise an error here.
+		 */
+		if (enabled) {
+			/* TODO: Change this portion of the code to use pre_
+			 * and post_ handler_allowed() routine
+			 */
+			if (type == HW_BREAKPOINT_EXECUTE)
+				bp->pre_handler = ptrace_triggered;
+			else
+				bp->post_handler = ptrace_triggered;
+
+			bp->priority = HW_BREAKPOINT_PRIO_PTRACE;
+			if (rc == 0 && __register_user_hw_breakpoint(tsk, bp,
+					bp->info.address, len, type) < 0)
+				break;
+		}
+	}
+
+	/* If anything above failed, restore the original settings */
+	if (i < HB_NUM) {
+		rc = -EIO;
+		data = old_dr7;
+		goto restore_settings;
+	}
+	return rc;
+}
+
+/*
+ * Handle PTRACE_POKEUSR calls for the debug register area.
+ */
+int thread_set_debugreg(struct task_struct *tsk, int n, unsigned long val)
+{
+	struct thread_hw_breakpoint *thbi;
+	int rc = -EIO;
+
+	/* We have to hold this lock the entire time, to prevent thbi
+	 * from being deallocated out from under us.
+	 */
+	mutex_lock(&hw_breakpoint_mutex);
+
+	/* There are no DR4 or DR5 registers */
+	if (n == 4 || n == 5)
+		;
+
+	/* Writes to DR6 modify the virtualized value */
+	else if (n == 6) {
+		tsk->thread.vdr6 = val;
+		rc = 0;
+	}
+
+	else if (!tsk->thread.hw_breakpoint_info && val == 0)
+		rc = 0;		/* Minor optimization */
+
+	else if ((thbi = alloc_thread_hw_breakpoint(tsk)) == NULL)
+		rc = -ENOMEM;
+
+	/* Writes to DR0 - DR3 change a breakpoint address */
+	else if (n < HB_NUM) {
+		struct hw_breakpoint *bp = &thbi->vdr_bps[n];
+
+		/* If the breakpoint is registered then unregister it,
+		 * change it, and re-register it.  Revert to the original
+		 * address if an error occurs.
+		 */
+		if (bp->status) {
+			unsigned long old_addr = bp->info.address;
+
+			__unregister_user_hw_breakpoint(tsk, bp);
+			rc = __register_user_hw_breakpoint(tsk, bp,
+					val, bp->info.len, bp->info.type);
+			if (rc < 0) {
+				__register_user_hw_breakpoint(tsk, bp,
+						old_addr,
+						bp->info.len, bp->info.type);
+			}
+		} else {
+			bp->info.address = val;
+			rc = 0;
+		}
+	}
+
+	/* All that's left is DR7 */
+	else
+		rc = ptrace_write_dr7(tsk, thbi, val);
+
+	mutex_unlock(&hw_breakpoint_mutex);
+	return rc;
+}
+
+
+/*
+ * Handle debug exception notifications.
+ */
+
+static void switch_to_none_hw_breakpoint(void);
+struct hw_breakpoint *last_hit_bp;
+struct thread_hw_breakpoint *last_hit_thbi;
+
+static int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+	struct cpu_hw_breakpoint *chbi;
+	int i;
+	struct hw_breakpoint *bp;
+	struct thread_hw_breakpoint *thbi = NULL;
+	unsigned int *ssr = &(__get_cpu_var(sstep_reason));
+
+	/* The DR6 value is stored in args->err */
+#define DR6	(args->err)
+
+	chbi = &per_cpu(cpu_info, get_cpu());
+
+	/* Disable all breakpoints so that the callbacks can run without
+	 * triggering recursive debug exceptions.
+	 */
+	set_debugreg(0UL, 7);
+
+	if ((DR6 & DR_STEP) && !((*ssr) & SSTEP_HWBKPT))
+		return NOTIFY_DONE;
+
+	/* If none of the breakpoint detection flags are enabled, it means we
+	 * have arrived here due to single-stepping of a target instruction
+	 */
+	if ((!(DR6 & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))) &&
+						(DR6 & DR_STEP)) {
+		args->regs->flags &= ~X86_EFLAGS_TF;
+		(*ssr) &= ~SSTEP_HWBKPT;
+		(last_hit_bp->post_handler)(last_hit_bp, args->regs);
+		/* Re-enable the breakpoints */
+		set_debugreg(last_hit_thbi ? last_hit_thbi->tkdr7 :
+						chbi->cur_kbpdata->mkdr7, 7);
+		put_cpu_no_resched();
+		current->thread.vdr6 &= ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3);
+
+		return NOTIFY_STOP;
+	}
+
+	/* Assert that local interrupts are disabled */
+	/* Reset the DRn bits in the virtualized register value.
+	 * The ptrace trigger routine will add in whatever is needed.
+	 */
+	current->thread.vdr6 &= ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3);
+
+	/* Are we a victim of lazy debug-register switching? */
+	if (!chbi->bp_task)
+		;
+	else if (chbi->bp_task != current) {
+
+		/* No user breakpoints are valid.  Perform the belated
+		 * debug-register switch.
+		 */
+		switch_to_none_hw_breakpoint();
+	} else {
+		thbi = chbi->bp_task->thread.hw_breakpoint_info;
+	}
+
+	/* Handle all the breakpoints that were triggered */
+	for (i = 0; i < HB_NUM; ++i) {
+		if (likely(!(DR6 & (DR_TRAP0 << i))))
+			continue;
+
+		/* Find the corresponding hw_breakpoint structure and
+		 * invoke its triggered callback.
+		 */
+		if (i < chbi->cur_kbpdata->num_kbps)
+			bp = chbi->cur_kbpdata->bps[i];
+		else if (thbi)
+			bp = thbi->bps[i];
+		else		/* False alarm due to lazy DR switching */
+			continue;
+		if (bp) {
+			(*ssr) = 0;
+			/* Enable single-stepping over the watched insn */
+			switch (bp->info.type) {
+			case HW_BREAKPOINT_EXECUTE:
+				if (bp->pre_handler)
+					(bp->pre_handler)(bp, args->regs);
+
+				if (bp->post_handler) {
+					(*ssr) |= SSTEP_HWBKPT;
+					args->regs->flags |=
+						(X86_EFLAGS_TF | X86_EFLAGS_RF);
+					last_hit_bp = bp;
+					last_hit_thbi = thbi;
+					return NOTIFY_DONE;
+				}
+				break;
+			case HW_BREAKPOINT_WRITE:
+			case HW_BREAKPOINT_RW:
+				if (bp->post_handler)
+					(bp->post_handler)(bp, args->regs);
+				/* Re-enable the breakpoints */
+				set_debugreg(thbi ? thbi->tkdr7 :
+						chbi->cur_kbpdata->mkdr7, 7);
+				put_cpu_no_resched();
+
+				return NOTIFY_DONE;
+			}
+		}
+	}
+	/* Stop processing further if the exception is a stray one */
+	if (!(DR6 & ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)))
+		return NOTIFY_STOP;
+
+	return NOTIFY_DONE;
+#undef DR6
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+static int __kprobes hw_breakpoint_exceptions_notify(
+		struct notifier_block *unused, unsigned long val, void *data)
+{
+int ret;
+
+	if (val != DIE_DEBUG)
+		return NOTIFY_DONE;
+	ret = hw_breakpoint_handler(data);
+	return ret;
+}
+
+static struct notifier_block hw_breakpoint_exceptions_nb = {
+	.notifier_call = hw_breakpoint_exceptions_notify,
+	.priority = 0x00
+};
+
+static int __init init_hw_breakpoint(void)
+{
+	load_debug_registers();
+	return register_die_notifier(&hw_breakpoint_exceptions_nb);
+}
+
+core_initcall(init_hw_breakpoint);
+
+
+/* Grab the arch-independent code */
+#include "../../../kernel/hw_breakpoint.c"
+
Index: linux-bkpt-lkml-27-rc9/include/asm-x86/hw_breakpoint.h
===================================================================
--- /dev/null
+++ linux-bkpt-lkml-27-rc9/include/asm-x86/hw_breakpoint.h
@@ -0,0 +1,121 @@
+#ifndef	_I386_HW_BREAKPOINT_H
+#define	_I386_HW_BREAKPOINT_H
+
+#ifdef	__KERNEL__
+#define	__ARCH_HW_BREAKPOINT_H
+
+struct arch_hw_breakpoint {
+	unsigned long	address;
+	u8		len;
+	u8		type;
+} __attribute__((packed));
+
+#include <asm-generic/hw_breakpoint.h>
+
+/* HW breakpoint accessor routines */
+static inline const void *hw_breakpoint_get_kaddress(struct hw_breakpoint *bp)
+{
+	return (const void *) bp->info.address;
+}
+
+static inline const void __user *hw_breakpoint_get_uaddress
+						(struct hw_breakpoint *bp)
+{
+	return (const void __user *) bp->info.address;
+}
+
+static inline unsigned hw_breakpoint_get_len(struct hw_breakpoint *bp)
+{
+	return bp->info.len;
+}
+
+static inline unsigned hw_breakpoint_get_type(struct hw_breakpoint *bp)
+{
+	return bp->info.type;
+}
+
+/* Available HW breakpoint length encodings */
+#define HW_BREAKPOINT_LEN_1		0x40
+#define HW_BREAKPOINT_LEN_2		0x44
+#define HW_BREAKPOINT_LEN_4		0x4c
+#define HW_BREAKPOINT_LEN_EXECUTE	0x40
+
+/* Available HW breakpoint type encodings */
+#define HW_BREAKPOINT_EXECUTE	0x80	/* trigger on instruction execute */
+#define HW_BREAKPOINT_WRITE	0x81	/* trigger on memory write */
+#define HW_BREAKPOINT_IO	0x82	/* trigger on I/O reads or writes */
+#define HW_BREAKPOINT_RW	0x83	/* trigger on memory read or write */
+
+#define HB_NUM 4
+
+/* Per-thread HW breakpoint and debug register info */
+struct thread_hw_breakpoint {
+
+	/* utrace support */
+	struct list_head	node;		/* Entry in thread list */
+	struct list_head	thread_bps;	/* Thread's breakpoints */
+	struct hw_breakpoint	*bps[HB_NUM];	/* Highest-priority bps */
+	unsigned long		tdr[HB_NUM];	/*  and their addresses */
+	int			num_installed;	/* Number of installed bps */
+	unsigned		gennum;		/* update-generation number */
+
+	/* Only the portions below are arch-specific */
+
+	/* ptrace support -- Note that vdr6 is stored directly in the
+	 * thread_struct so that it is always available.
+	 */
+	unsigned long		vdr7;			/* Virtualized DR7 */
+	struct hw_breakpoint	vdr_bps[HB_NUM];	/* Breakpoints
+			representing virtualized debug registers 0 - 3 */
+	unsigned long		tdr7;		/* Thread's DR7 value */
+	unsigned long		tkdr7;		/* Thread + kernel DR7 value */
+};
+
+/* Kernel-space breakpoint data */
+struct kernel_bp_data {
+	unsigned		gennum;		/* Generation number */
+	int			num_kbps;	/* Number of kernel bps */
+	struct hw_breakpoint	*bps[HB_NUM];	/* Loaded breakpoints */
+
+	/* Only the portions below are arch-specific */
+	unsigned long		mkdr7;		/* Masked kernel DR7 value */
+};
+
+/* Per-CPU debug register info */
+struct cpu_hw_breakpoint {
+	struct kernel_bp_data	*cur_kbpdata;	/* Current kbpdata[] entry */
+	struct task_struct	*bp_task;	/* The thread whose bps
+			are currently loaded in the debug registers */
+};
+
+/* Global info */
+static struct kernel_bp_data	kbpdata[2];	/* Old and new settings */
+static int			cur_kbpindex;	/* Alternates 0, 1, ... */
+static struct kernel_bp_data	*cur_kbpdata = &kbpdata[0];
+			/* Always equal to &kbpdata[cur_kbpindex] */
+
+static u8			tprio[HB_NUM];	/* Thread bp max priorities */
+static LIST_HEAD(kernel_bps);			/* Kernel breakpoint list */
+static LIST_HEAD(thread_list);			/* thread_hw_breakpoint list */
+static DEFINE_MUTEX(hw_breakpoint_mutex);	/* Protects everything */
+
+/* Only the portions below are arch-specific */
+
+static unsigned long		kdr7;		/* Unmasked kernel DR7 value */
+
+/* Masks for the bits in DR7 related to kernel breakpoints, for various
+ * values of num_kbps.  Entry n is the mask for when there are n kernel
+ * breakpoints, in debug registers 0 - (n-1).  The DR_GLOBAL_SLOWDOWN bit
+ * (GE) is handled specially.
+ */
+static const unsigned long	kdr7_masks[HB_NUM + 1] = {
+	0x00000000,
+	0x000f0003,	/* LEN0, R/W0, G0, L0 */
+	0x00ff000f,	/* Same for 0,1 */
+	0x0fff003f,	/* Same for 0,1,2 */
+	0xffff00ff	/* Same for 0,1,2,3 */
+};
+
+#endif	/* __KERNEL__ */
+#endif	/* _I386_HW_BREAKPOINT_H */
+
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/Makefile
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/Makefile
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/Makefile
@@ -33,7 +33,7 @@ obj-$(CONFIG_X86_64)	+= sys_x86_64.o x86
 obj-$(CONFIG_X86_64)	+= syscall_64.o vsyscall_64.o
 obj-y			+= bootflag.o e820.o
 obj-y			+= pci-dma.o quirks.o i8237.o topology.o kdebugfs.o
-obj-y			+= alternative.o i8253.o pci-nommu.o
+obj-y			+= alternative.o i8253.o pci-nommu.o hw_breakpoint.o
 obj-y			+= tsc.o io_delay.o rtc.o
 
 obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline.o

Re: [RFC Patch 2/9] x86 architecture implementation of Hardware Breakpoint interfaces

[Alan Stern]

On Tue, 7 Oct 2008, K.Prasad wrote:

> This patch introduces two new files named hw_breakpoint.[ch] inside x86 specific
> directories. They contain functions which help validate and serve requests for 
> using Hardware Breakpoint registers on x86 processors.

> --- /dev/null
> +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/hw_breakpoint.c
> @@ -0,0 +1,684 @@

...
> +int pre_handler_allowed(unsigned type)
> +{
> +	if (type == HW_BREAKPOINT_EXECUTE)
> +		return 1;
> +	else
> +		return -EINVAL;
> +}

The routine's name should match the name in the header file.  "allowed" 
isn't right: You're _allowed_ to have pre_handlers -- they just won't 
get invoked.  "supported" would be better.

Also, the comment in the header file should explain the meaning of the
return value -- you should return 0 if a pre_handler is not supported, 
not -EINVAL.  Better yet, define the function (both here and in the 
header file) as returning bool rather than int.

> +
> +int post_handler_allowed(unsigned type)
> +{
> +	/* We can have a post handler for all types of breakpoints */
> +	return 1;
> +}

Same comments as above.

Also, in this initial version I would prefer to avoid the complications
of single-stepping.  It can always be added later.  So for now, the x86
implementation should not support post_handlers for execution
breakpoints.

...
> +/*
> + * Validate the arch-specific HW Breakpoint register settings
> + */
> +static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
> +			unsigned long address, unsigned len, unsigned int type,
> +			unsigned int *align)

Why did you move this routine into the arch-specific code?

...
> +/*
> + * Handle debug exception notifications.
> + */
> +
> +static void switch_to_none_hw_breakpoint(void);
> +struct hw_breakpoint *last_hit_bp;
> +struct thread_hw_breakpoint *last_hit_thbi;

Shouldn't these variables be static?  Although if they're needed only for
single-stepping, they can be removed entirely for now...

Re: [RFC Patch 2/9] x86 architecture implementation of Hardware Breakpoint interfaces

[K.Prasad]

On Tue, Oct 07, 2008 at 11:36:30AM -0400, Alan Stern wrote:
> On Tue, 7 Oct 2008, K.Prasad wrote:
> 
> > This patch introduces two new files named hw_breakpoint.[ch] inside x86 specific
> > directories. They contain functions which help validate and serve requests for 
> > using Hardware Breakpoint registers on x86 processors.
> 
> > --- /dev/null
> > +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/hw_breakpoint.c
> > @@ -0,0 +1,684 @@
> 
> ...
> > +int pre_handler_allowed(unsigned type)
> > +{
> > +	if (type == HW_BREAKPOINT_EXECUTE)
> > +		return 1;
> > +	else
> > +		return -EINVAL;
> > +}
> 
> The routine's name should match the name in the header file.  "allowed" 
> isn't right: You're _allowed_ to have pre_handlers -- they just won't 
> get invoked.  "supported" would be better.

pre_handler_supported() definitely sounds better. I will change them.

> 
> Also, the comment in the header file should explain the meaning of the
> return value -- you should return 0 if a pre_handler is not supported, 
> not -EINVAL.  Better yet, define the function (both here and in the 
> header file) as returning bool rather than int.
>

I will change them to boolean.
 
> > +
> > +int post_handler_allowed(unsigned type)
> > +{
> > +	/* We can have a post handler for all types of breakpoints */
> > +	return 1;
> > +}
> 
> Same comments as above.
> 
> Also, in this initial version I would prefer to avoid the complications
> of single-stepping.  It can always be added later.  So for now, the x86
> implementation should not support post_handlers for execution
> breakpoints.
> 

There's been a perceivable inclination to let the user learn the
limitations/features of the underlying processor's breakpointing ability
(since the previous email mail thread on this topic) and the routines
pre_ and post_handler_allowed() are just a step towards that.

I can nullify the post_handler for x86-instruction breakpoint for now,
but it wouldn't simplify things very extensively (but for a few lines of
code in hw_breakpoint_handler() and the flag 'sstep_reason'). It also
benefits the code by bringing an understanding that there can be
multiple users of processor single-stepping (and therefore the need to
de-multiplex the exception and invoke the appropriate handler).

Left to me, I would like to retain the post_handler routine, unless you
strongly feel otherwise.

> ...
> > +/*
> > + * Validate the arch-specific HW Breakpoint register settings
> > + */
> > +static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
> > +			unsigned long address, unsigned len, unsigned int type,
> > +			unsigned int *align)
> 
> Why did you move this routine into the arch-specific code?
> 
> ...
> > +/*
> > + * Handle debug exception notifications.
> > + */
> > +
> > +static void switch_to_none_hw_breakpoint(void);
> > +struct hw_breakpoint *last_hit_bp;
> > +struct thread_hw_breakpoint *last_hit_thbi;
> 
> Shouldn't these variables be static?  Although if they're needed only for
> single-stepping, they can be removed entirely for now...
> 
Agreed. Will make them static.

Thanks,
K.Prasad

Re: [RFC Patch 2/9] x86 architecture implementation of Hardware Breakpoint interfaces

[Alan Stern]

On Tue, 7 Oct 2008, K.Prasad wrote:

> There's been a perceivable inclination to let the user learn the
> limitations/features of the underlying processor's breakpointing ability
> (since the previous email mail thread on this topic) and the routines
> pre_ and post_handler_allowed() are just a step towards that.
> 
> I can nullify the post_handler for x86-instruction breakpoint for now,
> but it wouldn't simplify things very extensively (but for a few lines of
> code in hw_breakpoint_handler() and the flag 'sstep_reason'). It also
> benefits the code by bringing an understanding that there can be
> multiple users of processor single-stepping (and therefore the need to
> de-multiplex the exception and invoke the appropriate handler).
> 
> Left to me, I would like to retain the post_handler routine, unless you
> strongly feel otherwise.

Let's hear what Roland has to say.

Alan Stern

Re: [RFC Patch 2/9] x86 architecture implementation of Hardware Breakpoint interfaces

[K.Prasad]

On Tue, Oct 07, 2008 at 11:36:30AM -0400, Alan Stern wrote:
> On Tue, 7 Oct 2008, K.Prasad wrote:
> 
> > This patch introduces two new files named hw_breakpoint.[ch] inside x86 specific
> > directories. They contain functions which help validate and serve requests for 
> > using Hardware Breakpoint registers on x86 processors.
> 
> > --- /dev/null
> > +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/hw_breakpoint.c
> > @@ -0,0 +1,684 @@
> 
> ...
> > +int pre_handler_allowed(unsigned type)
> > +{
> > +	if (type == HW_BREAKPOINT_EXECUTE)
> > +		return 1;
> > +	else
> > +		return -EINVAL;
> > +}
> 
> The routine's name should match the name in the header file.  "allowed" 
> isn't right: You're _allowed_ to have pre_handlers -- they just won't 
> get invoked.  "supported" would be better.
> 
> Also, the comment in the header file should explain the meaning of the
> return value -- you should return 0 if a pre_handler is not supported, 
> not -EINVAL.  Better yet, define the function (both here and in the 
> header file) as returning bool rather than int.
> 
> > +
> > +int post_handler_allowed(unsigned type)
> > +{
> > +	/* We can have a post handler for all types of breakpoints */
> > +	return 1;
> > +}
> 
> Same comments as above.
> 
> Also, in this initial version I would prefer to avoid the complications
> of single-stepping.  It can always be added later.  So for now, the x86
> implementation should not support post_handlers for execution
> breakpoints.
> 
> ...
> > +/*
> > + * Validate the arch-specific HW Breakpoint register settings
> > + */
> > +static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
> > +			unsigned long address, unsigned len, unsigned int type,
> > +			unsigned int *align)
> 
> Why did you move this routine into the arch-specific code?
>

I missed a reply for this comment in my previous mail.

Given that arch_validate_hwbkpt_settings() validates the type of
breakpoint operation requested and length of address to be monitored -
both of which are specific to the underlying processor architecture, I
thought it would be appropriate to place them in
arch/x86/kernel/hw_breakpoint.c.

Thanks,
K.Prasad

[RFC Patch 3/9] Modifying generic debug exception to use virtual debug registers

[K.Prasad]

This patch modifies the breakpoint exception handler code to use the abstract
register names.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/traps_32.c |   67 ++++++++++++++++-----------------------------
 arch/x86/kernel/traps_64.c |   64 ++++++++++++++++++++----------------------
 2 files changed, 54 insertions(+), 77 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/traps_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_32.c
@@ -890,11 +890,12 @@ void __kprobes do_int3(struct pt_regs *r
 void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
 	struct task_struct *tsk = current;
-	unsigned int condition;
+	unsigned long dr6;
 
 	trace_hardirqs_fixup();
 
-	get_debugreg(condition, 6);
+	get_debugreg(dr6, 6);
+	set_debugreg(0, 6);	/* DR6 may or may not be cleared by the CPU */
 
 	/*
 	 * The processor cleared BTF, so don't mark that we need it set.
@@ -902,60 +903,40 @@ void __kprobes do_debug(struct pt_regs *
 	clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
 	tsk->thread.debugctlmsr = 0;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
-						SIGTRAP) == NOTIFY_STOP)
+	/* Store the virtualized DR6 value */
+	tsk->thread.vdr6 = dr6;
+
+	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
+			SIGTRAP) == NOTIFY_STOP)
 		return;
 	/* It's safe to allow irq's after DR6 has been saved */
 	if (regs->flags & X86_EFLAGS_IF)
 		local_irq_enable();
 
-	/* Mask out spurious debug traps due to lazy DR7 setting */
-	if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
-		if (!tsk->thread.debugreg7)
-			goto clear_dr7;
+	if (regs->flags & X86_VM_MASK) {
+		handle_vm86_trap((struct kernel_vm86_regs *) regs,
+				error_code, 1);
+		return;
 	}
 
-	if (regs->flags & X86_VM_MASK)
-		goto debug_vm86;
-
-	/* Save debug status register where ptrace can see it */
-	tsk->thread.debugreg6 = condition;
-
 	/*
-	 * Single-stepping through TF: make sure we ignore any events in
-	 * kernel space (but re-enable TF when returning to user mode).
+	 * Single-stepping through system calls: ignore any exceptions in
+	 * kernel space, but re-enable TF when returning to user mode.
+	 *
+	 * We already checked v86 mode above, so we can check for kernel mode
+	 * by just checking the CPL of CS.
 	 */
-	if (condition & DR_STEP) {
-		/*
-		 * We already checked v86 mode above, so we can
-		 * check for kernel mode by just checking the CPL
-		 * of CS.
-		 */
-		if (!user_mode(regs))
-			goto clear_TF_reenable;
+	if ((dr6 & DR_STEP) && !user_mode(regs)) {
+		tsk->thread.vdr6 &= ~DR_STEP;
+		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+		regs->flags &= ~X86_EFLAGS_TF;
 	}
 
-	/* Ok, finally something we can handle */
-	send_sigtrap(tsk, regs, error_code);
-
-	/*
-	 * Disable additional traps. They'll be re-enabled when
-	 * the signal is delivered.
-	 */
-clear_dr7:
-	set_debugreg(0, 7);
-	return;
-
-debug_vm86:
-	handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
-	return;
-
-clear_TF_reenable:
-	set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-	regs->flags &= ~X86_EFLAGS_TF;
-	return;
+	if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
+		send_sigtrap(tsk, regs, error_code);
 }
 
+
 /*
  * Note that we play around with the 'TS' bit in an attempt to get
  * the correct behaviour even in the presence of the asynchronous
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/traps_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/traps_64.c
@@ -894,13 +894,14 @@ asmlinkage __kprobes struct pt_regs *syn
 asmlinkage void __kprobes do_debug(struct pt_regs * regs,
 				   unsigned long error_code)
 {
+	unsigned long dr6;;
 	struct task_struct *tsk = current;
-	unsigned long condition;
 	siginfo_t info;
 
 	trace_hardirqs_fixup();
 
-	get_debugreg(condition, 6);
+	get_debugreg(dr6, 6);
+	set_debugreg(0, 6);	/* DR6 may or may not be cleared by the CPU */
 
 	/*
 	 * The processor cleared BTF, so don't mark that we need it set.
@@ -908,48 +909,43 @@ asmlinkage void __kprobes do_debug(struc
 	clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
 	tsk->thread.debugctlmsr = 0;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
-						SIGTRAP) == NOTIFY_STOP)
+	/* Store the virtualized DR6 value */
+	tsk->thread.vdr6 = dr6;
+
+	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
+			SIGTRAP) == NOTIFY_STOP)
 		return;
 
 	preempt_conditional_sti(regs);
 
-	/* Mask out spurious debug traps due to lazy DR7 setting */
-	if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
-		if (!tsk->thread.debugreg7)
-			goto clear_dr7;
+	if (regs->flags & X86_VM_MASK) {
+		handle_vm86_trap((struct kernel_vm86_regs *) regs,
+				error_code, 1);
+		return;
 	}
 
-	tsk->thread.debugreg6 = condition;
-
 	/*
-	 * Single-stepping through TF: make sure we ignore any events in
-	 * kernel space (but re-enable TF when returning to user mode).
+	 * Single-stepping through system calls: ignore any exceptions in
+	 * kernel space, but re-enable TF when returning to user mode.
+	 *
+	 * We already checked v86 mode above, so we can check for kernel mode
+	 * by just checking the CPL of CS.
 	 */
-	if (condition & DR_STEP) {
-		if (!user_mode(regs))
-			goto clear_TF_reenable;
+	if ((dr6 & DR_STEP) && !user_mode(regs)) {
+		tsk->thread.vdr6 &= ~DR_STEP;
+		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+		regs->flags &= ~X86_EFLAGS_TF;
 	}
 
-	/* Ok, finally something we can handle */
-	tsk->thread.trap_no = 1;
-	tsk->thread.error_code = error_code;
-	info.si_signo = SIGTRAP;
-	info.si_errno = 0;
-	info.si_code = TRAP_BRKPT;
-	info.si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
-	force_sig_info(SIGTRAP, &info, tsk);
-
-clear_dr7:
-	set_debugreg(0, 7);
-	preempt_conditional_cli(regs);
-	return;
-
-clear_TF_reenable:
-	set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-	regs->flags &= ~X86_EFLAGS_TF;
-	preempt_conditional_cli(regs);
-	return;
+	if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
+		tsk->thread.trap_no = 1;
+		tsk->thread.error_code = error_code;
+		info.si_signo = SIGTRAP;
+		info.si_errno = 0;
+		info.si_code = TRAP_BRKPT;
+		info.si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
+		force_sig_info(SIGTRAP, &info, tsk);
+	}
 }
 
 static int kernel_math_error(struct pt_regs *regs, const char *str, int trapnr)

[RFC Patch 4/9] Modify kprobe exception handler to recognise single-stepping by HW Breakpoint handler

[K.Prasad]

This patch modifies the kprobe handler to help it recognise single-stepping by
the HW Breakpoint exception code. A per-cpu variable called 'sstep_reason' to
distinguish the source of single-step exceptions.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/kprobes.c |   18 ++++++++++++++++--
 include/asm-x86/kprobes.h |    8 ++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/kprobes.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/kprobes.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/kprobes.c
@@ -54,6 +54,7 @@
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
 #include <asm/alternative.h>
+#include <asm/debugreg.h>
 
 void jprobe_return_end(void);
 
@@ -517,6 +518,7 @@ static int __kprobes kprobe_handler(stru
 	kprobe_opcode_t *addr;
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
+	unsigned int *ssr;
 
 	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
 	if (*addr != BREAKPOINT_INSTRUCTION) {
@@ -541,6 +543,7 @@ static int __kprobes kprobe_handler(stru
 	 */
 	preempt_disable();
 
+	ssr = &(__get_cpu_var(sstep_reason));
 	kcb = get_kprobe_ctlblk();
 	p = get_kprobe(addr);
 
@@ -560,14 +563,17 @@ static int __kprobes kprobe_handler(stru
 			 * for jprobe processing, so get out doing nothing
 			 * more here.
 			 */
-			if (!p->pre_handler || !p->pre_handler(p, regs))
+			if (!p->pre_handler || !p->pre_handler(p, regs)) {
 				setup_singlestep(p, regs, kcb);
+				(*ssr) |= SSTEP_KPROBE;
+			}
 			return 1;
 		}
 	} else if (kprobe_running()) {
 		p = __get_cpu_var(current_kprobe);
 		if (p->break_handler && p->break_handler(p, regs)) {
 			setup_singlestep(p, regs, kcb);
+			(*ssr) |= SSTEP_KPROBE;
 			return 1;
 		}
 	} /* else: not a kprobe fault; let the kernel handle it */
@@ -952,6 +958,7 @@ int __kprobes kprobe_exceptions_notify(s
 {
 	struct die_args *args = data;
 	int ret = NOTIFY_DONE;
+	unsigned int *ssr = &(__get_cpu_var(sstep_reason));
 
 	if (args->regs && user_mode_vm(args->regs))
 		return ret;
@@ -962,8 +969,15 @@ int __kprobes kprobe_exceptions_notify(s
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_DEBUG:
-		if (post_kprobe_handler(args->regs))
+		/* We could be here due to single-stepping after a pre-handler
+		 * execution of HW Breakpoint or kprobes. We determine the cause
+		 * using the bitmask flag 'sstep_reason'.
+		 */
+		if (((*ssr) & SSTEP_KPROBE) &&
+					post_kprobe_handler(args->regs)) {
+			current->thread.vdr6 &= ~DR_STEP;
 			ret = NOTIFY_STOP;
+		}
 		break;
 	case DIE_GPF:
 		/*
Index: linux-bkpt-lkml-27-rc9/include/asm-x86/kprobes.h
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/include/asm-x86/kprobes.h
+++ linux-bkpt-lkml-27-rc9/include/asm-x86/kprobes.h
@@ -30,6 +30,14 @@
 struct pt_regs;
 struct kprobe;
 
+/* Single stepping can be initiated for kprobes post handler or following HW
+ * Breakpoint exception. The bitmask below is used to identify the cause.
+ */
+#define SSTEP_KPROBE 1
+#define SSTEP_HWBKPT 2
+
+DECLARE_PER_CPU(unsigned int, sstep_reason);
+
 typedef u8 kprobe_opcode_t;
 #define BREAKPOINT_INSTRUCTION	0xcc
 #define RELATIVEJUMP_INSTRUCTION 0xe9

[RFC Patch 5/9] Use wrapper routines around debug registers in processor related functions

[K.Prasad]

This patch enables the use of wrapper routines to access the debug/breakpoint
registers.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/smpboot.c   |    3 +++
 arch/x86/power/cpu_32.c     |   16 +++-------------
 arch/x86/power/cpu_64.c     |   15 +++------------
 include/asm-x86/debugreg.h  |   29 +++++++++++++++++++++++++++++
 include/asm-x86/processor.h |   10 +++-------
 5 files changed, 41 insertions(+), 32 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/power/cpu_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/power/cpu_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/power/cpu_32.c
@@ -11,6 +11,7 @@
 #include <linux/suspend.h>
 #include <asm/mtrr.h>
 #include <asm/mce.h>
+#include <asm/debugreg.h>
 
 static struct saved_context saved_context;
 
@@ -46,6 +47,7 @@ static void __save_processor_state(struc
 	ctxt->cr2 = read_cr2();
 	ctxt->cr3 = read_cr3();
 	ctxt->cr4 = read_cr4_safe();
+	disable_debug_registers();
 }
 
 /* Needed by apm.c */
@@ -78,19 +80,7 @@ static void fix_processor_context(void)
 	load_TR_desc();				/* This does ltr */
 	load_LDT(&current->active_mm->context);	/* This does lldt */
 
-	/*
-	 * Now maybe reload the debug registers
-	 */
-	if (current->thread.debugreg7) {
-		set_debugreg(current->thread.debugreg0, 0);
-		set_debugreg(current->thread.debugreg1, 1);
-		set_debugreg(current->thread.debugreg2, 2);
-		set_debugreg(current->thread.debugreg3, 3);
-		/* no 4 and 5 */
-		set_debugreg(current->thread.debugreg6, 6);
-		set_debugreg(current->thread.debugreg7, 7);
-	}
-
+	load_debug_registers();
 }
 
 static void __restore_processor_state(struct saved_context *ctxt)
Index: linux-bkpt-lkml-27-rc9/arch/x86/power/cpu_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/power/cpu_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/power/cpu_64.c
@@ -14,6 +14,7 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/mtrr.h>
+#include <asm/debugreg.h>
 
 static void fix_processor_context(void);
 
@@ -69,6 +70,7 @@ static void __save_processor_state(struc
 	ctxt->cr3 = read_cr3();
 	ctxt->cr4 = read_cr4();
 	ctxt->cr8 = read_cr8();
+	disable_debug_registers();
 }
 
 void save_processor_state(void)
@@ -151,16 +153,5 @@ static void fix_processor_context(void)
 	load_TR_desc();				/* This does ltr */
 	load_LDT(&current->active_mm->context);	/* This does lldt */
 
-	/*
-	 * Now maybe reload the debug registers
-	 */
-	if (current->thread.debugreg7){
-                loaddebug(&current->thread, 0);
-                loaddebug(&current->thread, 1);
-                loaddebug(&current->thread, 2);
-                loaddebug(&current->thread, 3);
-                /* no 4 and 5 */
-                loaddebug(&current->thread, 6);
-                loaddebug(&current->thread, 7);
-	}
+	load_debug_registers();
 }
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/smpboot.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/smpboot.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/smpboot.c
@@ -61,6 +61,7 @@
 #include <asm/mtrr.h>
 #include <asm/vmi.h>
 #include <asm/genapic.h>
+#include <asm/debugreg.h>
 #include <linux/mc146818rtc.h>
 
 #include <mach_apic.h>
@@ -342,6 +343,7 @@ static void __cpuinit start_secondary(vo
 	setup_secondary_clock();
 
 	wmb();
+	load_debug_registers();
 	cpu_idle();
 }
 
@@ -1382,6 +1384,7 @@ int __cpu_disable(void)
 	remove_cpu_from_maps(cpu);
 	unlock_vector_lock();
 	fixup_irqs(cpu_online_map);
+	disable_debug_registers();
 	return 0;
 }
 
Index: linux-bkpt-lkml-27-rc9/include/asm-x86/debugreg.h
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/include/asm-x86/debugreg.h
+++ linux-bkpt-lkml-27-rc9/include/asm-x86/debugreg.h
@@ -49,6 +49,8 @@
 
 #define DR_LOCAL_ENABLE_SHIFT 0    /* Extra shift to the local enable bit */
 #define DR_GLOBAL_ENABLE_SHIFT 1   /* Extra shift to the global enable bit */
+#define DR_LOCAL_ENABLE (0x1)      /* Local enable for reg 0 */
+#define DR_GLOBAL_ENABLE (0x2)     /* Global enable for reg 0 */
 #define DR_ENABLE_SIZE 2           /* 2 enable bits per register */
 
 #define DR_LOCAL_ENABLE_MASK (0x55)  /* Set  local bits for all 4 regs */
@@ -67,4 +69,31 @@
 #define DR_LOCAL_SLOWDOWN (0x100)   /* Local slow the pipeline */
 #define DR_GLOBAL_SLOWDOWN (0x200)  /* Global slow the pipeline */
 
+/*
+ * HW breakpoint additions
+ */
+#ifdef __KERNEL__
+
+#define HB_NUM		4	/* Number of hardware breakpoints */
+
+/* For process management */
+void flush_thread_hw_breakpoint(struct task_struct *tsk);
+int copy_thread_hw_breakpoint(struct task_struct *tsk,
+		struct task_struct *child, unsigned long clone_flags);
+void dump_thread_hw_breakpoint(struct task_struct *tsk, int u_debugreg[8]);
+void switch_to_thread_hw_breakpoint(struct task_struct *tsk);
+
+/* For CPU management */
+void load_debug_registers(void);
+static inline void disable_debug_registers(void)
+{
+	set_debugreg(0UL, 7);
+}
+
+/* For use by ptrace */
+unsigned long thread_get_debugreg(struct task_struct *tsk, int n);
+int thread_set_debugreg(struct task_struct *tsk, int n, unsigned long val);
+
+#endif	/* __KERNEL__ */
+
 #endif
Index: linux-bkpt-lkml-27-rc9/include/asm-x86/processor.h
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/include/asm-x86/processor.h
+++ linux-bkpt-lkml-27-rc9/include/asm-x86/processor.h
@@ -381,13 +381,9 @@ struct thread_struct {
 	unsigned long		ip;
 	unsigned long		fs;
 	unsigned long		gs;
-	/* Hardware debugging registers: */
-	unsigned long		debugreg0;
-	unsigned long		debugreg1;
-	unsigned long		debugreg2;
-	unsigned long		debugreg3;
-	unsigned long		debugreg6;
-	unsigned long		debugreg7;
+/* Hardware breakpoint info */
+	unsigned long	vdr6;
+	struct thread_hw_breakpoint	*hw_breakpoint_info;
 	/* Fault info: */
 	unsigned long		cr2;
 	unsigned long		trap_no;

[RFC Patch 6/9] Use virtual debug registers in process/thread handling code

[K.Prasad]

This patch enables the use of abstract/virtual debug registers in
process-handling routines.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/process_32.c |   68 +++++++++++++++++++++++++------------------
 arch/x86/kernel/process_64.c |   65 ++++++++++++++++++++++++-----------------
 2 files changed, 79 insertions(+), 54 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/process_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_32.c
@@ -56,6 +56,8 @@
 #include <asm/cpu.h>
 #include <asm/kdebug.h>
 #include <asm/idle.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
 
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
 
@@ -158,9 +160,11 @@ void cpu_idle(void)
 void __show_registers(struct pt_regs *regs, int all)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
-	unsigned long d0, d1, d2, d3, d6, d7;
+	unsigned long u_debugreg[8];
 	unsigned long sp;
 	unsigned short ss, gs;
+	struct thread_hw_breakpoint *thbi = current->thread.hw_breakpoint_info;
+	int i;
 
 	if (user_mode_vm(regs)) {
 		sp = regs->sp;
@@ -201,17 +205,18 @@ void __show_registers(struct pt_regs *re
 	printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
 			cr0, cr2, cr3, cr4);
 
-	get_debugreg(d0, 0);
-	get_debugreg(d1, 1);
-	get_debugreg(d2, 2);
-	get_debugreg(d3, 3);
+	if (thbi) {
+		for (i = 0; i < HB_NUM; ++i)
+			u_debugreg[i] = thbi->vdr_bps[i].info.address;
+		u_debugreg[7] = thbi->vdr7;
+	}
+	u_debugreg[6] = current->thread.vdr6;
+
 	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
-			d0, d1, d2, d3);
+					u_debugreg[0], u_debugreg[1],
+						u_debugreg[2], u_debugreg[3]);
 
-	get_debugreg(d6, 6);
-	get_debugreg(d7, 7);
-	printk("DR6: %08lx DR7: %08lx\n",
-			d6, d7);
+	printk("DR6: %08lx DR7: %08lx\n", u_debugreg[6], u_debugreg[7]);
 }
 
 void show_regs(struct pt_regs *regs)
@@ -257,6 +262,8 @@ EXPORT_SYMBOL(kernel_thread);
  */
 void exit_thread(void)
 {
+	struct task_struct *tsk = current;
+
 	/* The process may have allocated an io port bitmap... nuke it. */
 	if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
 		struct task_struct *tsk = current;
@@ -277,20 +284,17 @@ void exit_thread(void)
 		tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 		put_cpu();
 	}
+	if (unlikely(tsk->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(tsk);
 }
 
 void flush_thread(void)
 {
 	struct task_struct *tsk = current;
 
-	tsk->thread.debugreg0 = 0;
-	tsk->thread.debugreg1 = 0;
-	tsk->thread.debugreg2 = 0;
-	tsk->thread.debugreg3 = 0;
-	tsk->thread.debugreg6 = 0;
-	tsk->thread.debugreg7 = 0;
-	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
-	clear_tsk_thread_flag(tsk, TIF_DEBUG);
+	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
+	if (unlikely(tsk->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(tsk);
 	/*
 	 * Forget coprocessor state..
 	 */
@@ -334,7 +338,15 @@ int copy_thread(int nr, unsigned long cl
 
 	savesegment(gs, p->thread.gs);
 
+	p->thread.hw_breakpoint_info = NULL;
+	p->thread.io_bitmap_ptr = NULL;
+
 	tsk = current;
+	err = -ENOMEM;
+	if (unlikely(tsk->thread.hw_breakpoint_info)) {
+		if (copy_thread_hw_breakpoint(tsk, p, clone_flags))
+			goto out;
+	}
 	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
 		p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
 						IO_BITMAP_BYTES, GFP_KERNEL);
@@ -354,10 +366,14 @@ int copy_thread(int nr, unsigned long cl
 		err = do_set_thread_area(p, -1,
 			(struct user_desc __user *)childregs->si, 0);
 
+out:
 	if (err && p->thread.io_bitmap_ptr) {
 		kfree(p->thread.io_bitmap_ptr);
 		p->thread.io_bitmap_max = 0;
 	}
+	if (err)
+		flush_thread_hw_breakpoint(p);
+
 	return err;
 }
 
@@ -460,16 +476,6 @@ __switch_to_xtra(struct task_struct *pre
 	if (next->debugctlmsr != debugctl)
 		update_debugctlmsr(next->debugctlmsr);
 
-	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
-		set_debugreg(next->debugreg0, 0);
-		set_debugreg(next->debugreg1, 1);
-		set_debugreg(next->debugreg2, 2);
-		set_debugreg(next->debugreg3, 3);
-		/* no 4 and 5 */
-		set_debugreg(next->debugreg6, 6);
-		set_debugreg(next->debugreg7, 7);
-	}
-
 	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
 	    test_tsk_thread_flag(next_p, TIF_NOTSC)) {
 		/* prev and next are different */
@@ -625,6 +631,12 @@ struct task_struct * __switch_to(struct 
 		loadsegment(gs, next->gs);
 
 	x86_write_percpu(current_task, next_p);
+	/*
+	 * Handle debug registers.  This must be done _after_ current
+	 * is updated.
+	 */
+	if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+		switch_to_thread_hw_breakpoint(next_p);
 
 	return prev_p;
 }
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/process_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_64.c
@@ -51,6 +51,8 @@
 #include <asm/proto.h>
 #include <asm/ia32.h>
 #include <asm/idle.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
 
 asmlinkage extern void ret_from_fork(void);
 
@@ -156,9 +158,11 @@ void cpu_idle(void)
 void __show_regs(struct pt_regs * regs)
 {
 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
-	unsigned long d0, d1, d2, d3, d6, d7;
+	unsigned long u_debugreg[8];
 	unsigned int fsindex, gsindex;
 	unsigned int ds, cs, es;
+	struct thread_hw_breakpoint *thbi = current->thread.hw_breakpoint_info;
+	int i;
 
 	printk("\n");
 	print_modules();
@@ -202,14 +206,17 @@ void __show_regs(struct pt_regs * regs)
 	printk("CS:  %04x DS: %04x ES: %04x CR0: %016lx\n", cs, ds, es, cr0); 
 	printk("CR2: %016lx CR3: %016lx CR4: %016lx\n", cr2, cr3, cr4);
 
-	get_debugreg(d0, 0);
-	get_debugreg(d1, 1);
-	get_debugreg(d2, 2);
-	printk("DR0: %016lx DR1: %016lx DR2: %016lx\n", d0, d1, d2);
-	get_debugreg(d3, 3);
-	get_debugreg(d6, 6);
-	get_debugreg(d7, 7);
-	printk("DR3: %016lx DR6: %016lx DR7: %016lx\n", d3, d6, d7);
+	if (thbi) {
+		for (i = 0; i < HB_NUM; ++i)
+			u_debugreg[i] = thbi->vdr_bps[i].info.address;
+		u_debugreg[7] = thbi->vdr7;
+	}
+	u_debugreg[6] = current->thread.vdr6;
+
+	printk("DR0: %016lx DR1: %016lx DR2: %016lx\n", u_debugreg[0],
+						u_debugreg[1], u_debugreg[2]);
+	printk("DR3: %016lx DR6: %016lx DR7: %016lx\n", u_debugreg[3],
+						u_debugreg[6], u_debugreg[7]);
 }
 
 void show_regs(struct pt_regs *regs)
@@ -240,6 +247,8 @@ void exit_thread(void)
 		t->io_bitmap_max = 0;
 		put_cpu();
 	}
+	if (unlikely(me->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(me);
 }
 
 void flush_thread(void)
@@ -257,13 +266,9 @@ void flush_thread(void)
 	}
 	clear_tsk_thread_flag(tsk, TIF_DEBUG);
 
-	tsk->thread.debugreg0 = 0;
-	tsk->thread.debugreg1 = 0;
-	tsk->thread.debugreg2 = 0;
-	tsk->thread.debugreg3 = 0;
-	tsk->thread.debugreg6 = 0;
-	tsk->thread.debugreg7 = 0;
 	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
+	if (unlikely(tsk->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(tsk);
 	/*
 	 * Forget coprocessor state..
 	 */
@@ -338,13 +343,21 @@ int copy_thread(int nr, unsigned long cl
 
 	p->thread.fs = me->thread.fs;
 	p->thread.gs = me->thread.gs;
+	p->thread.hw_breakpoint_info = NULL;
+	p->thread.io_bitmap_ptr = NULL;
 
 	savesegment(gs, p->thread.gsindex);
 	savesegment(fs, p->thread.fsindex);
 	savesegment(es, p->thread.es);
 	savesegment(ds, p->thread.ds);
 
-	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
+	err = -ENOMEM;
+	if (unlikely(me->thread.hw_breakpoint_info)) {
+		if (copy_thread_hw_breakpoint(me, p, clone_flags))
+			goto out;
+	}
+
+if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
 		p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
 		if (!p->thread.io_bitmap_ptr) {
 			p->thread.io_bitmap_max = 0;
@@ -375,6 +388,9 @@ out:
 		kfree(p->thread.io_bitmap_ptr);
 		p->thread.io_bitmap_max = 0;
 	}
+	if (err)
+		flush_thread_hw_breakpoint(p);
+
 	return err;
 }
 
@@ -484,16 +500,6 @@ static inline void __switch_to_xtra(stru
 	if (next->debugctlmsr != debugctl)
 		update_debugctlmsr(next->debugctlmsr);
 
-	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
-		loaddebug(next, 0);
-		loaddebug(next, 1);
-		loaddebug(next, 2);
-		loaddebug(next, 3);
-		/* no 4 and 5 */
-		loaddebug(next, 6);
-		loaddebug(next, 7);
-	}
-
 	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
 	    test_tsk_thread_flag(next_p, TIF_NOTSC)) {
 		/* prev and next are different */
@@ -524,6 +530,13 @@ static inline void __switch_to_xtra(stru
 	if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
 		ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
 #endif
+
+/*
+	 * Handle debug registers.  This must be done _after_ current
+	 * is updated.
+	 */
+	if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+		switch_to_thread_hw_breakpoint(next_p);
 }
 
 /*

Re: [RFC Patch 6/9] Use virtual debug registers in process/thread handling code

[Alan Stern]

On Tue, 7 Oct 2008, K.Prasad wrote:

> This patch enables the use of abstract/virtual debug registers in
> process-handling routines.

...
> --- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/process_32.c
> +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_32.c
> @@ -56,6 +56,8 @@
>  #include <asm/cpu.h>
>  #include <asm/kdebug.h>
>  #include <asm/idle.h>
> +#include <asm/debugreg.h>
> +#include <asm/hw_breakpoint.h>
>  
>  asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
>  
> @@ -158,9 +160,11 @@ void cpu_idle(void)
>  void __show_registers(struct pt_regs *regs, int all)
>  {
>  	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
> -	unsigned long d0, d1, d2, d3, d6, d7;
> +	unsigned long u_debugreg[8];
>  	unsigned long sp;
>  	unsigned short ss, gs;
> +	struct thread_hw_breakpoint *thbi = current->thread.hw_breakpoint_info;
> +	int i;
>  
>  	if (user_mode_vm(regs)) {
>  		sp = regs->sp;
> @@ -201,17 +205,18 @@ void __show_registers(struct pt_regs *re
>  	printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
>  			cr0, cr2, cr3, cr4);
>  
> -	get_debugreg(d0, 0);
> -	get_debugreg(d1, 1);
> -	get_debugreg(d2, 2);
> -	get_debugreg(d3, 3);
> +	if (thbi) {
> +		for (i = 0; i < HB_NUM; ++i)
> +			u_debugreg[i] = thbi->vdr_bps[i].info.address;
> +		u_debugreg[7] = thbi->vdr7;
> +	}
> +	u_debugreg[6] = current->thread.vdr6;
> +
>  	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
> -			d0, d1, d2, d3);
> +					u_debugreg[0], u_debugreg[1],
> +						u_debugreg[2], u_debugreg[3]);
>  
> -	get_debugreg(d6, 6);
> -	get_debugreg(d7, 7);
> -	printk("DR6: %08lx DR7: %08lx\n",
> -			d6, d7);
> +	printk("DR6: %08lx DR7: %08lx\n", u_debugreg[6], u_debugreg[7]);

I don't like this at all.  show_registers() should display the physical
register contents, not the virtualized values.  Ditto for the 64-byte
version of this routine.

Alan Stern

Re: [RFC Patch 6/9] Use virtual debug registers in process/thread handling code

[K.Prasad]

On Tue, Oct 07, 2008 at 11:40:46AM -0400, Alan Stern wrote:
> On Tue, 7 Oct 2008, K.Prasad wrote:
> 
> > This patch enables the use of abstract/virtual debug registers in
> > process-handling routines.
> 
> ...
> > --- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/process_32.c
> > +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_32.c
> > @@ -56,6 +56,8 @@
> >  #include <asm/cpu.h>
> >  #include <asm/kdebug.h>
> >  #include <asm/idle.h>
> > +#include <asm/debugreg.h>
> > +#include <asm/hw_breakpoint.h>
> >  
> >  asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
> >  
> > @@ -158,9 +160,11 @@ void cpu_idle(void)
> >  void __show_registers(struct pt_regs *regs, int all)
> >  {
> >  	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
> > -	unsigned long d0, d1, d2, d3, d6, d7;
> > +	unsigned long u_debugreg[8];
> >  	unsigned long sp;
> >  	unsigned short ss, gs;
> > +	struct thread_hw_breakpoint *thbi = current->thread.hw_breakpoint_info;
> > +	int i;
> >  
> >  	if (user_mode_vm(regs)) {
> >  		sp = regs->sp;
> > @@ -201,17 +205,18 @@ void __show_registers(struct pt_regs *re
> >  	printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
> >  			cr0, cr2, cr3, cr4);
> >  
> > -	get_debugreg(d0, 0);
> > -	get_debugreg(d1, 1);
> > -	get_debugreg(d2, 2);
> > -	get_debugreg(d3, 3);
> > +	if (thbi) {
> > +		for (i = 0; i < HB_NUM; ++i)
> > +			u_debugreg[i] = thbi->vdr_bps[i].info.address;
> > +		u_debugreg[7] = thbi->vdr7;
> > +	}
> > +	u_debugreg[6] = current->thread.vdr6;
> > +
> >  	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
> > -			d0, d1, d2, d3);
> > +					u_debugreg[0], u_debugreg[1],
> > +						u_debugreg[2], u_debugreg[3]);
> >  
> > -	get_debugreg(d6, 6);
> > -	get_debugreg(d7, 7);
> > -	printk("DR6: %08lx DR7: %08lx\n",
> > -			d6, d7);
> > +	printk("DR6: %08lx DR7: %08lx\n", u_debugreg[6], u_debugreg[7]);
> 
> I don't like this at all.  show_registers() should display the physical
> register contents, not the virtualized values.  Ditto for the 64-byte
> version of this routine.
> 
> Alan Stern
> 
Agreed, will modify this!

Thanks,
K.Prasad

[RFC Patch 7/9] Modify signal handling code to refrain from re-enabling HW Breakpoints

[K.Prasad]

This patch disables re-enabling of Hardware Breakpoint registers through the 
signal handling code. This is now during hw_breakpoint_handler().

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/signal_32.c |    9 ---------
 arch/x86/kernel/signal_64.c |    8 --------
 2 files changed, 17 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/signal_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/signal_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/signal_32.c
@@ -600,15 +600,6 @@ static void do_signal(struct pt_regs *re
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
-		/*
-		 * Re-enable any watchpoints before delivering the
-		 * signal to user space. The processor register will
-		 * have been cleared if the watchpoint triggered
-		 * inside the kernel.
-		 */
-		if (current->thread.debugreg7)
-			set_debugreg(current->thread.debugreg7, 7);
-
 		/* Whee! Actually deliver the signal.  */
 		if (handle_signal(signr, &info, &ka, oldset, regs) == 0) {
 			/*
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/signal_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/signal_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/signal_64.c
@@ -496,14 +496,6 @@ static void do_signal(struct pt_regs *re
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
-		/* Re-enable any watchpoints before delivering the
-		 * signal to user space. The processor register will
-		 * have been cleared if the watchpoint triggered
-		 * inside the kernel.
-		 */
-		if (current->thread.debugreg7)
-			set_debugreg(current->thread.debugreg7, 7);
-
 		/* Whee!  Actually deliver the signal.  */
 		if (handle_signal(signr, &info, &ka, oldset, regs) == 0) {
 			/*

[RFC Patch 8/9] Modify Ptrace to use wrapper routines to access breakpoint registers

[K.Prasad]

This patch modifies the ptrace code to use the new wrapper routines around the 
debug/breakpoint registers.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/ptrace.c |  101 +----------------------------------------------
 1 file changed, 4 insertions(+), 97 deletions(-)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/ptrace.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/ptrace.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/ptrace.c
@@ -462,98 +462,6 @@ static int genregs_set(struct task_struc
 	return ret;
 }
 
-/*
- * This function is trivial and will be inlined by the compiler.
- * Having it separates the implementation details of debug
- * registers from the interface details of ptrace.
- */
-static unsigned long ptrace_get_debugreg(struct task_struct *child, int n)
-{
-	switch (n) {
-	case 0:		return child->thread.debugreg0;
-	case 1:		return child->thread.debugreg1;
-	case 2:		return child->thread.debugreg2;
-	case 3:		return child->thread.debugreg3;
-	case 6:		return child->thread.debugreg6;
-	case 7:		return child->thread.debugreg7;
-	}
-	return 0;
-}
-
-static int ptrace_set_debugreg(struct task_struct *child,
-			       int n, unsigned long data)
-{
-	int i;
-
-	if (unlikely(n == 4 || n == 5))
-		return -EIO;
-
-	if (n < 4 && unlikely(data >= debugreg_addr_limit(child)))
-		return -EIO;
-
-	switch (n) {
-	case 0:		child->thread.debugreg0 = data; break;
-	case 1:		child->thread.debugreg1 = data; break;
-	case 2:		child->thread.debugreg2 = data; break;
-	case 3:		child->thread.debugreg3 = data; break;
-
-	case 6:
-		if ((data & ~0xffffffffUL) != 0)
-			return -EIO;
-		child->thread.debugreg6 = data;
-		break;
-
-	case 7:
-		/*
-		 * Sanity-check data. Take one half-byte at once with
-		 * check = (val >> (16 + 4*i)) & 0xf. It contains the
-		 * R/Wi and LENi bits; bits 0 and 1 are R/Wi, and bits
-		 * 2 and 3 are LENi. Given a list of invalid values,
-		 * we do mask |= 1 << invalid_value, so that
-		 * (mask >> check) & 1 is a correct test for invalid
-		 * values.
-		 *
-		 * R/Wi contains the type of the breakpoint /
-		 * watchpoint, LENi contains the length of the watched
-		 * data in the watchpoint case.
-		 *
-		 * The invalid values are:
-		 * - LENi == 0x10 (undefined), so mask |= 0x0f00.	[32-bit]
-		 * - R/Wi == 0x10 (break on I/O reads or writes), so
-		 *   mask |= 0x4444.
-		 * - R/Wi == 0x00 && LENi != 0x00, so we have mask |=
-		 *   0x1110.
-		 *
-		 * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
-		 *
-		 * See the Intel Manual "System Programming Guide",
-		 * 15.2.4
-		 *
-		 * Note that LENi == 0x10 is defined on x86_64 in long
-		 * mode (i.e. even for 32-bit userspace software, but
-		 * 64-bit kernel), so the x86_64 mask value is 0x5454.
-		 * See the AMD manual no. 24593 (AMD64 System Programming)
-		 */
-#ifdef CONFIG_X86_32
-#define	DR7_MASK	0x5f54
-#else
-#define	DR7_MASK	0x5554
-#endif
-		data &= ~DR_CONTROL_RESERVED;
-		for (i = 0; i < 4; i++)
-			if ((DR7_MASK >> ((data >> (16 + 4*i)) & 0xf)) & 1)
-				return -EIO;
-		child->thread.debugreg7 = data;
-		if (data)
-			set_tsk_thread_flag(child, TIF_DEBUG);
-		else
-			clear_tsk_thread_flag(child, TIF_DEBUG);
-		break;
-	}
-
-	return 0;
-}
-
 #ifdef X86_BTS
 
 static int ptrace_bts_get_size(struct task_struct *child)
@@ -888,7 +796,7 @@ long arch_ptrace(struct task_struct *chi
 		else if (addr >= offsetof(struct user, u_debugreg[0]) &&
 			 addr <= offsetof(struct user, u_debugreg[7])) {
 			addr -= offsetof(struct user, u_debugreg[0]);
-			tmp = ptrace_get_debugreg(child, addr / sizeof(data));
+			tmp = thread_get_debugreg(child, addr/sizeof(data));
 		}
 		ret = put_user(tmp, datap);
 		break;
@@ -905,8 +813,7 @@ long arch_ptrace(struct task_struct *chi
 		else if (addr >= offsetof(struct user, u_debugreg[0]) &&
 			 addr <= offsetof(struct user, u_debugreg[7])) {
 			addr -= offsetof(struct user, u_debugreg[0]);
-			ret = ptrace_set_debugreg(child,
-						  addr / sizeof(data), data);
+			ret = thread_set_debugreg(child, addr/sizeof(data), data);
 		}
 		break;
 
@@ -1073,7 +980,7 @@ static int putreg32(struct task_struct *
 	case offsetof(struct user32, u_debugreg[0]) ...
 		offsetof(struct user32, u_debugreg[7]):
 		regno -= offsetof(struct user32, u_debugreg[0]);
-		return ptrace_set_debugreg(child, regno / 4, value);
+		return thread_set_debugreg(child, regno / 4, value);
 
 	default:
 		if (regno > sizeof(struct user32) || (regno & 3))
@@ -1132,7 +1039,7 @@ static int getreg32(struct task_struct *
 	case offsetof(struct user32, u_debugreg[0]) ...
 		offsetof(struct user32, u_debugreg[7]):
 		regno -= offsetof(struct user32, u_debugreg[0]);
-		*val = ptrace_get_debugreg(child, regno / 4);
+		*val = thread_get_debugreg(child, regno / 4);
 		break;
 
 	default:

[RFC Patch 9/9] Cleanup HW Breakpoint registers before kexec

[K.Prasad]

This patch disables Hardware breakpoints before doing a 'kexec' on the machine.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
 arch/x86/kernel/machine_kexec_32.c |    2 ++
 arch/x86/kernel/machine_kexec_64.c |    2 ++
 2 files changed, 4 insertions(+)

Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/machine_kexec_32.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/machine_kexec_32.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/machine_kexec_32.c
@@ -24,6 +24,7 @@
 #include <asm/desc.h>
 #include <asm/system.h>
 #include <asm/cacheflush.h>
+#include <asm/debugreg.h>
 
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
 static u32 kexec_pgd[1024] PAGE_ALIGNED;
@@ -131,6 +132,7 @@ void machine_kexec(struct kimage *image)
 
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
+	disable_debug_registers();
 
 	if (image->preserve_context) {
 #ifdef CONFIG_X86_IO_APIC
Index: linux-bkpt-lkml-27-rc9/arch/x86/kernel/machine_kexec_64.c
===================================================================
--- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/machine_kexec_64.c
+++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/machine_kexec_64.c
@@ -17,6 +17,7 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 #include <asm/io.h>
+#include <asm/debugreg.h>
 
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
 static u64 kexec_pgd[512] PAGE_ALIGNED;
@@ -190,6 +191,7 @@ void machine_kexec(struct kimage *image)
 
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
+	disable_debug_registers();
 
 	control_page = page_address(image->control_code_page) + PAGE_SIZE;
 	memcpy(control_page, relocate_kernel, PAGE_SIZE);

Re: [RFC Patch 0/9] Hardware Breakpoint interfaces

[Avi Kivity]

K.Prasad wrote:
> - Enable KGDB and KVM to use the register_kernel_hw_breakpoint()
>   interface for their HW Breakpoint usage, in the absence of which
>   they will be broken during simultaneous use.
>   

KVM conceptually isn't a kernel use of the debug registers.  KVM 
modifies the debug registers while the guest is running, and restores 
them after the guest returns.

Right now, as an optimization, KVM defers restoring the debug registers 
until after the next context switch out of the kvm task, or until the 
next exit to userspace (whichever comes earlier); we should change this 
to avoid the deferral if kernel breakpoints are in effect.  This will 
allow simultaneous use of KVM breakpoints and kernel breakpoints.

-- 
error compiling committee.c: too many arguments to function

Re: [RFC Patch 0/9] Hardware Breakpoint interfaces

[K.Prasad]

On Tue, Oct 07, 2008 at 02:29:05PM +0200, Avi Kivity wrote:
> K.Prasad wrote:
>> - Enable KGDB and KVM to use the register_kernel_hw_breakpoint()
>>   interface for their HW Breakpoint usage, in the absence of which
>>   they will be broken during simultaneous use.
>>   
>
> KVM conceptually isn't a kernel use of the debug registers.  KVM  
> modifies the debug registers while the guest is running, and restores  
> them after the guest returns.
>
> Right now, as an optimization, KVM defers restoring the debug registers  
> until after the next context switch out of the kvm task, or until the  
> next exit to userspace (whichever comes earlier); we should change this  
> to avoid the deferral if kernel breakpoints are in effect.  This will  
> allow simultaneous use of KVM breakpoints and kernel breakpoints.
>
The patch posted provides interface for using HW breakpoints on both
user- and kernel-space breakpoints. KVM's user-space address breakpoint
requirements, after code-modification, should be made to use
register_user_hw_breakpoint() interface (presently un-exported but will
be changed subsequently) to help maintain a system-wide consistent view on the
availability of HW Breakpoint registers.

Presently I find plenty of set_debugreg() calls from kvm/ which will
modify the registers directly and break the breakpoint register
management brought-in through the patch.

Thanks,
K.Prasad

Re: [RFC Patch 0/9] Hardware Breakpoint interfaces

[Avi Kivity]

K.Prasad wrote:
> On Tue, Oct 07, 2008 at 02:29:05PM +0200, Avi Kivity wrote:
>   
>> K.Prasad wrote:
>>     
>>> - Enable KGDB and KVM to use the register_kernel_hw_breakpoint()
>>>   interface for their HW Breakpoint usage, in the absence of which
>>>   they will be broken during simultaneous use.
>>>   
>>>       
>> KVM conceptually isn't a kernel use of the debug registers.  KVM  
>> modifies the debug registers while the guest is running, and restores  
>> them after the guest returns.
>>
>> Right now, as an optimization, KVM defers restoring the debug registers  
>> until after the next context switch out of the kvm task, or until the  
>> next exit to userspace (whichever comes earlier); we should change this  
>> to avoid the deferral if kernel breakpoints are in effect.  This will  
>> allow simultaneous use of KVM breakpoints and kernel breakpoints.
>>
>>     
> The patch posted provides interface for using HW breakpoints on both
> user- and kernel-space breakpoints. KVM's user-space address breakpoint
> requirements, after code-modification, should be made to use
> register_user_hw_breakpoint() interface (presently un-exported but will
> be changed subsequently) to help maintain a system-wide consistent view on the
> availability of HW Breakpoint registers.
>
>   

Correcting myself, actually kvm breakpoints are in a third namespace.  
You could have kernel breakpoints, user breakpoints, and guest 
breakpoints coexisting.

> Presently I find plenty of set_debugreg() calls from kvm/ which will
> modify the registers directly and break the breakpoint register
> management brought-in through the patch.
>   

If kvm restores the registers, should there be any problem?

-- 
error compiling committee.c: too many arguments to function

Re: [RFC Patch 0/9] Hardware Breakpoint interfaces

[K.Prasad]

On Tue, Oct 07, 2008 at 04:36:54PM +0200, Avi Kivity wrote:
> K.Prasad wrote:
>> On Tue, Oct 07, 2008 at 02:29:05PM +0200, Avi Kivity wrote:
>>   
>>> K.Prasad wrote:
>>>     
>>>> - Enable KGDB and KVM to use the register_kernel_hw_breakpoint()
>>>>   interface for their HW Breakpoint usage, in the absence of which
>>>>   they will be broken during simultaneous use.
>>>>         
>>> KVM conceptually isn't a kernel use of the debug registers.  KVM   
>>> modifies the debug registers while the guest is running, and restores 
>>>  them after the guest returns.
>>>
>>> Right now, as an optimization, KVM defers restoring the debug 
>>> registers  until after the next context switch out of the kvm task, 
>>> or until the  next exit to userspace (whichever comes earlier); we 
>>> should change this  to avoid the deferral if kernel breakpoints are 
>>> in effect.  This will  allow simultaneous use of KVM breakpoints and 
>>> kernel breakpoints.
>>>
>>>     
>> The patch posted provides interface for using HW breakpoints on both
>> user- and kernel-space breakpoints. KVM's user-space address breakpoint
>> requirements, after code-modification, should be made to use
>> register_user_hw_breakpoint() interface (presently un-exported but will
>> be changed subsequently) to help maintain a system-wide consistent view on the
>> availability of HW Breakpoint registers.
>>
>>   
>
> Correcting myself, actually kvm breakpoints are in a third namespace.   
> You could have kernel breakpoints, user breakpoints, and guest  
> breakpoints coexisting.
>
>> Presently I find plenty of set_debugreg() calls from kvm/ which will
>> modify the registers directly and break the breakpoint register
>> management brought-in through the patch.
>>   
>
> If kvm restores the registers, should there be any problem?
>
No, it should be fine although I don't understand how the exception
handler is invoked in KVM without the use of notifier or a hook in
die_debug (or have they replaced code at a layer much below that?).

Apart from the doubt I've stated above, if they operate by replacing
the breakpoint register contents before a context switch from KVM to
other processes, they might in fact help maximise its utilisation.

Thanks for the clarification!

Thanks,
K.Prasad

Re: [RFC Patch 0/9] Hardware Breakpoint interfaces

[Avi Kivity]

K.Prasad wrote:
>>
>>> Presently I find plenty of set_debugreg() calls from kvm/ which will
>>> modify the registers directly and break the breakpoint register
>>> management brought-in through the patch.
>>>   
>>>       
>> If kvm restores the registers, should there be any problem?
>>
>>     
> No, it should be fine although I don't understand how the exception
> handler is invoked in KVM without the use of notifier or a hook in
> die_debug (or have they replaced code at a layer much below that?).
>
>   

kvm debug traps don't work by raising a debug exception; instead, the 
guest #VMEXITs into the host.  The kernel debug handler will not be invoked.

> Apart from the doubt I've stated above, if they operate by replacing
> the breakpoint register contents before a context switch from KVM to
> other processes, they might in fact help maximise its utilisation.
>   

Yes.  As I mentioned, right now we avoid swapping the debug registers if 
we aren't going to context switch or exit to userspace, but if you give 
us a predicate that tells us whether you are interested in the debug 
registers, we can swap them eagerly rather than lazily.

-- 
error compiling committee.c: too many arguments to function