diff mbox series

[v9,4/7] arm64: smp: Assign and setup the debug IPI

Message ID 20230601143109.v9.4.I6d7f7d5fa0aa293c8c3374194947254b93114d37@changeid
State New
Headers
Series arm64: Add debug IPI for backtraces / kgdb; try to use NMI for it |

Commit Message

Doug Anderson June 1, 2023, 9:31 p.m. UTC 
  From: Sumit Garg <sumit.garg@linaro.org>

All current arm64 interrupt controllers have at least 8
IPIs. Currently we are only using 7 of them on arm64. Let's use the
8th one as a debug IPI. This uses the new "debug IPI" infrastructure
which will try to allocate this IPI as an NMI/pseudo NMI if possible.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
I could imagine that people object to using up the last free IPI on
interrupt controllers with only 8 IPIs. However, it shouldn't be a big
deal. If we later need an extra IPI, it shouldn't be too hard to
combine some of the existing ones. Presumably we could just get rid of
the "crash stop" IPI and have the normal "stop" IPI do the crash if
"waiting_for_crash_ipi" is non-zero

Changes in v9:
- Add a warning if we don't have enough IPIs for the NMI IPI
- Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.
- Update commit description

Changes in v8:
- debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param

 arch/arm64/kernel/smp.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Mark Rutland Aug. 7, 2023, 10:17 a.m. UTC | #1 
On Thu, Jun 01, 2023 at 02:31:48PM -0700, Douglas Anderson wrote:
> From: Sumit Garg <sumit.garg@linaro.org>
> 
> All current arm64 interrupt controllers have at least 8
> IPIs. Currently we are only using 7 of them on arm64. Let's use the
> 8th one as a debug IPI. This uses the new "debug IPI" infrastructure
> which will try to allocate this IPI as an NMI/pseudo NMI if possible.
> 
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

I think with my suggestion on the prior patch, we don't need the additional
logic here.

> ---
> I could imagine that people object to using up the last free IPI on
> interrupt controllers with only 8 IPIs. However, it shouldn't be a big
> deal. If we later need an extra IPI, it shouldn't be too hard to
> combine some of the existing ones. Presumably we could just get rid of
> the "crash stop" IPI and have the normal "stop" IPI do the crash if
> "waiting_for_crash_ipi" is non-zero

TBH, I'd love to unify the logic for IPI_CPU_STOP and IPI_CPU_CRASH_STOP as
they have a bunch of pointless divergence.

We could also remove IPI_WAKEUP and replace that with something else (e.g.
IPI_CALL_FUNC with an empty function) in order to free up an IPI.

I'd *also* prefer to have separate IPI_CPU_BACKTRACE and IPI_CPU_DEBUG as the
backtrace logic is used for a bunch of things other than KGDB (e.g. RCU stalls,
panic), and that would clearly separate the logic for the two cases.

Thanks,
Mark.

> 
> Changes in v9:
> - Add a warning if we don't have enough IPIs for the NMI IPI
> - Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.
> - Update commit description
> 
> Changes in v8:
> - debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param
> 
>  arch/arm64/kernel/smp.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index edd63894d61e..db019b49d3bd 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -53,6 +53,8 @@
>  
>  #include <trace/events/ipi.h>
>  
> +#include "ipi_debug.h"
> +
>  DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
>  EXPORT_PER_CPU_SYMBOL(cpu_number);
>  
> @@ -935,6 +937,8 @@ static void ipi_setup(int cpu)
>  
>  	for (i = 0; i < nr_ipi; i++)
>  		enable_percpu_irq(ipi_irq_base + i, 0);
> +
> +	debug_ipi_setup();
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> @@ -947,6 +951,8 @@ static void ipi_teardown(int cpu)
>  
>  	for (i = 0; i < nr_ipi; i++)
>  		disable_percpu_irq(ipi_irq_base + i);
> +
> +	debug_ipi_teardown();
>  }
>  #endif
>  
> @@ -968,6 +974,11 @@ void __init set_smp_ipi_range(int ipi_base, int n)
>  		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
>  	}
>  
> +	if (n > nr_ipi)
> +		set_smp_debug_ipi(ipi_base + nr_ipi);
> +	else
> +		WARN(1, "Not enough IPIs for NMI IPI\n");
> +
>  	ipi_irq_base = ipi_base;
>  
>  	/* Setup the boot CPU immediately */
> -- 
> 2.41.0.rc2.161.g9c6817b8e7-goog
>
diff mbox series

Patch

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index edd63894d61e..db019b49d3bd 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -53,6 +53,8 @@ 
 
 #include <trace/events/ipi.h>
 
+#include "ipi_debug.h"
+
 DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
 EXPORT_PER_CPU_SYMBOL(cpu_number);
 
@@ -935,6 +937,8 @@  static void ipi_setup(int cpu)
 
 	for (i = 0; i < nr_ipi; i++)
 		enable_percpu_irq(ipi_irq_base + i, 0);
+
+	debug_ipi_setup();
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -947,6 +951,8 @@  static void ipi_teardown(int cpu)
 
 	for (i = 0; i < nr_ipi; i++)
 		disable_percpu_irq(ipi_irq_base + i);
+
+	debug_ipi_teardown();
 }
 #endif
 
@@ -968,6 +974,11 @@  void __init set_smp_ipi_range(int ipi_base, int n)
 		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
 	}
 
+	if (n > nr_ipi)
+		set_smp_debug_ipi(ipi_base + nr_ipi);
+	else
+		WARN(1, "Not enough IPIs for NMI IPI\n");
+
 	ipi_irq_base = ipi_base;
 
 	/* Setup the boot CPU immediately */