[PATCH RFC v2 3/3] riscv: hw-breakpoints: add more trigger controls

Sergey Matyukevich
2022-12-03T21:56:02Z

From: Sergey Matyukevich <sergey.matyukevich@syntacore.com>

RISC-V SBI Debug Trigger extension proposal defines multiple functions
to control debug triggers. The pair of install/uninstall functions was
enough to implement ptrace interface for user-space debug. This patch
implements kernel wrappers for start/update/stop SBI functions. The
intended users of these control wrappers are kgdb and kernel modules
that make use of kernel-wide hardware breakpoints and watchpoints.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich@syntacore.com>
---
arch/riscv/include/asm/hw_breakpoint.h | 15 ++++
arch/riscv/kernel/hw_breakpoint.c | 116 ++++++++++++++++++++++++-
2 files changed, 127 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/hw_breakpoint.h b/arch/riscv/include/asm/hw_breakpoint.h
index 5bb3b55cd464..afc59f8e034e 100644
--- a/arch/riscv/include/asm/hw_breakpoint.h
+++ b/arch/riscv/include/asm/hw_breakpoint.h
@@ -137,6 +137,9 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
unsigned long val, void *data);

+void arch_enable_hw_breakpoint(struct perf_event *bp);
+void arch_update_hw_breakpoint(struct perf_event *bp);
+void arch_disable_hw_breakpoint(struct perf_event *bp);
int arch_install_hw_breakpoint(struct perf_event *bp);
void arch_uninstall_hw_breakpoint(struct perf_event *bp);
void hw_breakpoint_pmu_read(struct perf_event *bp);
@@ -153,5 +156,17 @@ static inline void clear_ptrace_hw_breakpoint(struct task_struct *tsk)
{
}

+void arch_enable_hw_breakpoint(struct perf_event *bp)
+{
+}
+
+void arch_update_hw_breakpoint(struct perf_event *bp)
+{
+}
+
+void arch_disable_hw_breakpoint(struct perf_event *bp)
+{
+}
+
#endif /* CONFIG_HAVE_HW_BREAKPOINT */
#endif /* __RISCV_HW_BREAKPOINT_H */
diff --git a/arch/riscv/kernel/hw_breakpoint.c b/arch/riscv/kernel/hw_breakpoint.c
index 8eddf512cd03..ca7df02830c2 100644
--- a/arch/riscv/kernel/hw_breakpoint.c
+++ b/arch/riscv/kernel/hw_breakpoint.c
@@ -2,6 +2,7 @@

#include <linux/hw_breakpoint.h>
#include <linux/perf_event.h>
+#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/kdebug.h>

@@ -9,6 +10,8 @@

/* bps/wps currently set on each debug trigger for each cpu */
static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM_MAX]);
+static DEFINE_PER_CPU(unsigned long, msg_lock_flags);
+static DEFINE_PER_CPU(raw_spinlock_t, msg_lock);

static struct sbi_dbtr_data_msg __percpu *sbi_xmit;
static struct sbi_dbtr_id_msg __percpu *sbi_recv;
@@ -318,6 +321,10 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
struct perf_event **slot;
unsigned long idx;
struct sbiret ret;
+ int err = 0;
+
+ raw_spin_lock_irqsave(this_cpu_ptr(&msg_lock),
+ *this_cpu_ptr(&msg_lock_flags));

xmit->tdata1 = cpu_to_lle(info->trig_data1.value);
xmit->tdata2 = cpu_to_lle(info->trig_data2);
@@ -328,25 +335,31 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
0, 0, 0);
if (ret.error) {
pr_warn("%s: failed to install trigger\n", __func__);
- return -EIO;
+ err = -EIO;
+ goto done;
}

idx = lle_to_cpu(recv->idx);

if (idx >= dbtr_total_num) {
pr_warn("%s: invalid trigger index %lu\n", __func__, idx);
- return -EINVAL;
+ err = -EINVAL;
+ goto done;
}

slot = this_cpu_ptr(&bp_per_reg[idx]);
if (*slot) {
pr_warn("%s: slot %lu is in use\n", __func__, idx);
- return -EBUSY;
+ err = -EBUSY;
+ goto done;
}

*slot = bp;

- return 0;
+done:
+ raw_spin_unlock_irqrestore(this_cpu_ptr(&msg_lock),
+ *this_cpu_ptr(&msg_lock_flags));
+ return err;
}

/* atomic: counter->ctx->lock is held */
@@ -375,6 +388,96 @@ void arch_uninstall_hw_breakpoint(struct perf_event *bp)
pr_warn("%s: failed to uninstall trigger %d\n", __func__, i);
}

+void arch_enable_hw_breakpoint(struct perf_event *bp)
+{
+ struct sbiret ret;
+ int i;
+
+ for (i = 0; i < dbtr_total_num; i++) {
+ struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
+
+ if (*slot == bp)
+ break;
+ }
+
+ if (i == dbtr_total_num) {
+ pr_warn("%s: unknown breakpoint\n", __func__);
+ return;
+ }
+
+ ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_TRIGGER_ENABLE,
+ i, 1, 0, 0, 0, 0);
+ if (ret.error) {
+ pr_warn("%s: failed to install trigger %d\n", __func__, i);
+ return;
+ }
+}
+EXPORT_SYMBOL_GPL(arch_enable_hw_breakpoint);
+
+void arch_update_hw_breakpoint(struct perf_event *bp)
+{
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+ struct sbi_dbtr_data_msg *xmit = this_cpu_ptr(sbi_xmit);
+ struct perf_event **slot;
+ struct sbiret ret;
+ int i;
+
+ for (i = 0; i < dbtr_total_num; i++) {
+ slot = this_cpu_ptr(&bp_per_reg[i]);
+
+ if (*slot == bp)
+ break;
+ }
+
+ if (i == dbtr_total_num) {
+ pr_warn("%s: unknown breakpoint\n", __func__);
+ return;
+ }
+
+ raw_spin_lock_irqsave(this_cpu_ptr(&msg_lock),
+ *this_cpu_ptr(&msg_lock_flags));
+
+ xmit->tdata1 = cpu_to_lle(info->trig_data1.value);
+ xmit->tdata2 = cpu_to_lle(info->trig_data2);
+ xmit->tdata3 = cpu_to_lle(info->trig_data3);
+
+ ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_TRIGGER_UPDATE,
+ i, 1, __pa(xmit) >> 4,
+ 0, 0, 0);
+ if (ret.error)
+ pr_warn("%s: failed to update trigger %d\n", __func__, i);
+
+ raw_spin_unlock_irqrestore(this_cpu_ptr(&msg_lock),
+ *this_cpu_ptr(&msg_lock_flags));
+}
+EXPORT_SYMBOL_GPL(arch_update_hw_breakpoint);
+
+void arch_disable_hw_breakpoint(struct perf_event *bp)
+{
+ struct sbiret ret;
+ int i;
+
+ for (i = 0; i < dbtr_total_num; i++) {
+ struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
+
+ if (*slot == bp)
+ break;
+ }
+
+ if (i == dbtr_total_num) {
+ pr_warn("%s: unknown breakpoint\n", __func__);
+ return;
+ }
+
+ ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_TRIGGER_DISABLE,
+ i, 1, 0, 0, 0, 0);
+ if (ret.error) {
+ pr_warn("%s: failed to uninstall trigger %d\n", __func__, i);
+ return;
+ }
+}
+EXPORT_SYMBOL_GPL(arch_disable_hw_breakpoint);
+
void hw_breakpoint_pmu_read(struct perf_event *bp)
{
}
@@ -406,6 +509,8 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)

static int __init arch_hw_breakpoint_init(void)
{
+ unsigned int cpu;
+
sbi_xmit = __alloc_percpu(sizeof(*sbi_xmit), SZ_16);
if (!sbi_xmit) {
pr_warn("failed to allocate SBI xmit message buffer\n");
@@ -418,6 +523,9 @@ static int __init arch_hw_breakpoint_init(void)
return -ENOMEM;
}

+ for_each_possible_cpu(cpu)
+ raw_spin_lock_init(&per_cpu(msg_lock, cpu));
+
if (!dbtr_init)
arch_hw_breakpoint_init_sbi();

--
2.38.1