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x86, hw_breakpoints, kgdb: Fix kgdb to use hw_breakpoint API
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In the 2.6.33 kernel, the hw_breakpoint API is now used for the
performance event counters.  The hw_breakpoint_handler() now
consumes the hw breakpoints that were previously set by kgdb
arch specific code.  In order for kgdb to work in conjunction
with this core API change, kgdb must use some of the low level
functions of the hw_breakpoint API to install, uninstall, and
deal with hw breakpoint reservations.

The kgdb core required a change to call kgdb_disable_hw_debug
anytime a slave cpu enters kgdb_wait() in order to keep all the
hw breakpoints in sync as well as to prevent hitting a hw
breakpoint while kgdb is active.

During the architecture specific initialization of kgdb, it will
pre-allocate 4 disabled (struct perf event **) structures.  Kgdb
will use these to manage the capabilities for the 4 hw
breakpoint registers, per cpu.  Right now the hw_breakpoint API
does not have a way to ask how many breakpoints are available,
on each CPU so it is possible that the install of a breakpoint
might fail when kgdb restores the system to the run state.  The
intent of this patch is to first get the basic functionality of
hw breakpoints working and leave it to the person debugging the
kernel to understand what hw breakpoints are in use and what
restrictions have been imposed as a result.  Breakpoint
constraints will be dealt with in a future patch.

While atomic, the x86 specific kgdb code will call
arch_uninstall_hw_breakpoint() and arch_install_hw_breakpoint()
to manage the cpu specific hw breakpoints.

The net result of these changes allow kgdb to use the same pool
of hw_breakpoints that are used by the perf event API, but
neither knows about future reservations for the available hw
breakpoint slots.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: kgdb-bugreport@lists.sourceforge.net
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: torvalds@linux-foundation.org
LKML-Reference: <1264719883-7285-2-git-send-email-jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Jason Wessel authored and Ingo Molnar committed Jan 30, 2010
1 parent b23ff0e commit cc09674
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Showing 2 changed files with 117 additions and 57 deletions.
171 changes: 114 additions & 57 deletions arch/x86/kernel/kgdb.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/nmi.h>
#include <linux/hw_breakpoint.h>

#include <asm/debugreg.h>
#include <asm/apicdef.h>
Expand Down Expand Up @@ -204,40 +205,38 @@ void gdb_regs_to_pt_regs(unsigned long *gdb_regs, struct pt_regs *regs)

static struct hw_breakpoint {
unsigned enabled;
unsigned type;
unsigned len;
unsigned long addr;
int len;
int type;
struct perf_event **pev;
} breakinfo[4];

static void kgdb_correct_hw_break(void)
{
unsigned long dr7;
int correctit = 0;
int breakbit;
int breakno;

get_debugreg(dr7, 7);
for (breakno = 0; breakno < 4; breakno++) {
breakbit = 2 << (breakno << 1);
if (!(dr7 & breakbit) && breakinfo[breakno].enabled) {
correctit = 1;
dr7 |= breakbit;
dr7 &= ~(0xf0000 << (breakno << 2));
dr7 |= ((breakinfo[breakno].len << 2) |
breakinfo[breakno].type) <<
((breakno << 2) + 16);
set_debugreg(breakinfo[breakno].addr, breakno);

} else {
if ((dr7 & breakbit) && !breakinfo[breakno].enabled) {
correctit = 1;
dr7 &= ~breakbit;
dr7 &= ~(0xf0000 << (breakno << 2));
}
}
struct perf_event *bp;
struct arch_hw_breakpoint *info;
int val;
int cpu = raw_smp_processor_id();
if (!breakinfo[breakno].enabled)
continue;
bp = *per_cpu_ptr(breakinfo[breakno].pev, cpu);
info = counter_arch_bp(bp);
if (bp->attr.disabled != 1)
continue;
bp->attr.bp_addr = breakinfo[breakno].addr;
bp->attr.bp_len = breakinfo[breakno].len;
bp->attr.bp_type = breakinfo[breakno].type;
info->address = breakinfo[breakno].addr;
info->len = breakinfo[breakno].len;
info->type = breakinfo[breakno].type;
val = arch_install_hw_breakpoint(bp);
if (!val)
bp->attr.disabled = 0;
}
if (correctit)
set_debugreg(dr7, 7);
hw_breakpoint_restore();
}

static int
Expand All @@ -259,15 +258,23 @@ kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
static void kgdb_remove_all_hw_break(void)
{
int i;
int cpu = raw_smp_processor_id();
struct perf_event *bp;

for (i = 0; i < 4; i++)
memset(&breakinfo[i], 0, sizeof(struct hw_breakpoint));
for (i = 0; i < 4; i++) {
if (!breakinfo[i].enabled)
continue;
bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
if (bp->attr.disabled == 1)
continue;
arch_uninstall_hw_breakpoint(bp);
bp->attr.disabled = 1;
}
}

static int
kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
{
unsigned type;
int i;

for (i = 0; i < 4; i++)
Expand All @@ -278,27 +285,38 @@ kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)

switch (bptype) {
case BP_HARDWARE_BREAKPOINT:
type = 0;
len = 1;
len = 1;
breakinfo[i].type = X86_BREAKPOINT_EXECUTE;
break;
case BP_WRITE_WATCHPOINT:
type = 1;
breakinfo[i].type = X86_BREAKPOINT_WRITE;
break;
case BP_ACCESS_WATCHPOINT:
type = 3;
breakinfo[i].type = X86_BREAKPOINT_RW;
break;
default:
return -1;
}

if (len == 1 || len == 2 || len == 4)
breakinfo[i].len = len - 1;
else
switch (len) {
case 1:
breakinfo[i].len = X86_BREAKPOINT_LEN_1;
break;
case 2:
breakinfo[i].len = X86_BREAKPOINT_LEN_2;
break;
case 4:
breakinfo[i].len = X86_BREAKPOINT_LEN_4;
break;
#ifdef CONFIG_X86_64
case 8:
breakinfo[i].len = X86_BREAKPOINT_LEN_8;
break;
#endif
default:
return -1;

breakinfo[i].enabled = 1;
}
breakinfo[i].addr = addr;
breakinfo[i].type = type;
breakinfo[i].enabled = 1;

return 0;
}
Expand All @@ -313,8 +331,21 @@ kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
*/
void kgdb_disable_hw_debug(struct pt_regs *regs)
{
int i;
int cpu = raw_smp_processor_id();
struct perf_event *bp;

/* Disable hardware debugging while we are in kgdb: */
set_debugreg(0UL, 7);
for (i = 0; i < 4; i++) {
if (!breakinfo[i].enabled)
continue;
bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
if (bp->attr.disabled == 1)
continue;
arch_uninstall_hw_breakpoint(bp);
bp->attr.disabled = 1;
}
}

/**
Expand Down Expand Up @@ -378,7 +409,6 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
struct pt_regs *linux_regs)
{
unsigned long addr;
unsigned long dr6;
char *ptr;
int newPC;

Expand All @@ -404,20 +434,6 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
raw_smp_processor_id());
}

get_debugreg(dr6, 6);
if (!(dr6 & 0x4000)) {
int breakno;

for (breakno = 0; breakno < 4; breakno++) {
if (dr6 & (1 << breakno) &&
breakinfo[breakno].type == 0) {
/* Set restore flag: */
linux_regs->flags |= X86_EFLAGS_RF;
break;
}
}
}
set_debugreg(0UL, 6);
kgdb_correct_hw_break();

return 0;
Expand Down Expand Up @@ -485,8 +501,7 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
break;

case DIE_DEBUG:
if (atomic_read(&kgdb_cpu_doing_single_step) ==
raw_smp_processor_id()) {
if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
if (user_mode(regs))
return single_step_cont(regs, args);
break;
Expand Down Expand Up @@ -539,7 +554,42 @@ static struct notifier_block kgdb_notifier = {
*/
int kgdb_arch_init(void)
{
return register_die_notifier(&kgdb_notifier);
int i, cpu;
int ret;
struct perf_event_attr attr;
struct perf_event **pevent;

ret = register_die_notifier(&kgdb_notifier);
if (ret != 0)
return ret;
/*
* Pre-allocate the hw breakpoint structions in the non-atomic
* portion of kgdb because this operation requires mutexs to
* complete.
*/
attr.bp_addr = (unsigned long)kgdb_arch_init;
attr.type = PERF_TYPE_BREAKPOINT;
attr.bp_len = HW_BREAKPOINT_LEN_1;
attr.bp_type = HW_BREAKPOINT_W;
attr.disabled = 1;
for (i = 0; i < 4; i++) {
breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL);
if (IS_ERR(breakinfo[i].pev)) {
printk(KERN_ERR "kgdb: Could not allocate hw breakpoints\n");
breakinfo[i].pev = NULL;
kgdb_arch_exit();
return -1;
}
for_each_online_cpu(cpu) {
pevent = per_cpu_ptr(breakinfo[i].pev, cpu);
pevent[0]->hw.sample_period = 1;
if (pevent[0]->destroy != NULL) {
pevent[0]->destroy = NULL;
release_bp_slot(*pevent);
}
}
}
return ret;
}

/**
Expand All @@ -550,6 +600,13 @@ int kgdb_arch_init(void)
*/
void kgdb_arch_exit(void)
{
int i;
for (i = 0; i < 4; i++) {
if (breakinfo[i].pev) {
unregister_wide_hw_breakpoint(breakinfo[i].pev);
breakinfo[i].pev = NULL;
}
}
unregister_die_notifier(&kgdb_notifier);
}

Expand Down
3 changes: 3 additions & 0 deletions kernel/kgdb.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -583,6 +583,9 @@ static void kgdb_wait(struct pt_regs *regs)
smp_wmb();
atomic_set(&cpu_in_kgdb[cpu], 1);

/* Disable any cpu specific hw breakpoints */
kgdb_disable_hw_debug(regs);

/* Wait till primary CPU is done with debugging */
while (atomic_read(&passive_cpu_wait[cpu]))
cpu_relax();
Expand Down

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