diff mbox series

[v11,6/6] arm64: kgdb: Implement kgdb_roundup_cpus() to enable pseudo-NMI roundup

Message ID 20230824083012.v11.6.I2ef26d1b3bfbed2d10a281942b0da7d9854de05e@changeid (mailing list archive)
State New, archived
Headers show
Series arm64: Add IPI for backtraces / kgdb; try to use NMI for some IPIs | expand

Commit Message

Doug Anderson Aug. 24, 2023, 3:30 p.m. UTC 
Up until now we've been using the generic (weak) implementation for
kgdb_roundup_cpus() when using kgdb on arm64. Let's move to a custom
one. The advantage here is that, when pseudo-NMI is enabled on a
device, we'll be able to round up CPUs using pseudo-NMI. This allows
us to debug CPUs that are stuck with interrupts disabled. If
pseudo-NMIs are not enabled then we'll fallback to just using an IPI,
which is still slightly better than the generic implementation since
it avoids the potential situation described in the generic
kgdb_call_nmi_hook().

Co-developed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
I debated whether this should be in "arch/arm64/kernel/smp.c" or if I
should try to find a way for it to go into "arch/arm64/kernel/kgdb.c".
In the end this is so little code that it didn't seem worth it to find
a way to export the IPI defines or to otherwise come up with some API
between kgdb.c and smp.c. If someone has strong feelings and wants
this to change, please shout and give details of your preferred
solution.

FWIW, it seems like ~half the other platforms put this in "smp.c" with
an ifdef for KGDB and the other half put it in "kgdb.c" with an ifdef
for SMP. :-P

(no changes since v10)

Changes in v10:
- Don't allocate the cpumask on the stack; just iterate.
- Moved kgdb calls to smp.c to avoid needing to export IPI info.
- kgdb now has its own IPI.

Changes in v9:
- Remove fallback for when debug IPI isn't available.
- Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.

 arch/arm64/kernel/smp.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

Comments

Daniel Thompson Aug. 25, 2023, 11:20 a.m. UTC | #1 
On Thu, Aug 24, 2023 at 08:30:32AM -0700, Douglas Anderson wrote:
> Up until now we've been using the generic (weak) implementation for
> kgdb_roundup_cpus() when using kgdb on arm64. Let's move to a custom
> one. The advantage here is that, when pseudo-NMI is enabled on a
> device, we'll be able to round up CPUs using pseudo-NMI. This allows
> us to debug CPUs that are stuck with interrupts disabled. If
> pseudo-NMIs are not enabled then we'll fallback to just using an IPI,
> which is still slightly better than the generic implementation since
> it avoids the potential situation described in the generic
> kgdb_call_nmi_hook().
>
> Co-developed-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

From a kgdb point of view:
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.
Stephen Boyd Aug. 25, 2023, 10:28 p.m. UTC | #2 
Quoting Douglas Anderson (2023-08-24 08:30:32)
> Up until now we've been using the generic (weak) implementation for
> kgdb_roundup_cpus() when using kgdb on arm64. Let's move to a custom
> one. The advantage here is that, when pseudo-NMI is enabled on a
> device, we'll be able to round up CPUs using pseudo-NMI. This allows
> us to debug CPUs that are stuck with interrupts disabled. If
> pseudo-NMIs are not enabled then we'll fallback to just using an IPI,
> which is still slightly better than the generic implementation since
> it avoids the potential situation described in the generic
> kgdb_call_nmi_hook().
>
> Co-developed-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
diff mbox series

Patch

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 4566934aaf9f..d440c8b21ea7 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -32,6 +32,7 @@ 
 #include <linux/irq_work.h>
 #include <linux/kernel_stat.h>
 #include <linux/kexec.h>
+#include <linux/kgdb.h>
 #include <linux/kvm_host.h>
 #include <linux/nmi.h>
 
@@ -79,6 +80,7 @@  enum ipi_msg_type {
 	 * with trace_ipi_*
 	 */
 	IPI_CPU_BACKTRACE = NR_IPI,
+	IPI_KGDB_ROUNDUP,
 	MAX_IPI
 };
 
@@ -868,6 +870,22 @@  void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
 	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, arm64_backtrace_ipi);
 }
 
+#ifdef CONFIG_KGDB
+void kgdb_roundup_cpus(void)
+{
+	int this_cpu = raw_smp_processor_id();
+	int cpu;
+
+	for_each_online_cpu(cpu) {
+		/* No need to roundup ourselves */
+		if (cpu == this_cpu)
+			continue;
+
+		__ipi_send_single(ipi_desc[IPI_KGDB_ROUNDUP], cpu);
+	}
+}
+#endif
+
 /*
  * Main handler for inter-processor interrupts
  */
@@ -919,6 +937,10 @@  static void do_handle_IPI(int ipinr)
 		nmi_cpu_backtrace(get_irq_regs());
 		break;
 
+	case IPI_KGDB_ROUNDUP:
+		kgdb_nmicallback(cpu, get_irq_regs());
+		break;
+
 	default:
 		pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
 		break;
@@ -949,6 +971,7 @@  static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
 	case IPI_CPU_STOP:
 	case IPI_CPU_CRASH_STOP:
 	case IPI_CPU_BACKTRACE:
+	case IPI_KGDB_ROUNDUP:
 		return true;
 	default:
 		return false;