There's no reason why IPI_CPU_STOP and IPI_CPU_CRASH_STOP can't be
handled as NMI. They are very simple and everything in them is
NMI-safe. Mark them as things to use NMI for if NMI is available.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
I don't actually have any good way to test/validate this patch. It's
added to the series at Mark's request.

(no changes since v10)

Changes in v10:
- ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10.

 arch/arm64/kernel/smp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index c8896cbc5327..4566934aaf9f 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -946,6 +946,8 @@ static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
 		return false;
 
 	switch (ipi) {
+	case IPI_CPU_STOP:
+	case IPI_CPU_CRASH_STOP:
 	case IPI_CPU_BACKTRACE:
 		return true;
 	default:
-- 
2.42.0.rc1.204.g551eb34607-goog

On Thu, 24 Aug 2023 at 21:03, Douglas Anderson <dianders@chromium.org> wrote:
>
> There's no reason why IPI_CPU_STOP and IPI_CPU_CRASH_STOP can't be
> handled as NMI. They are very simple and everything in them is
> NMI-safe. Mark them as things to use NMI for if NMI is available.
>
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>

-Sumit

> ---
> I don't actually have any good way to test/validate this patch. It's
> added to the series at Mark's request.
>
> (no changes since v10)
>
> Changes in v10:
> - ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for v10.
>
>  arch/arm64/kernel/smp.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index c8896cbc5327..4566934aaf9f 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -946,6 +946,8 @@ static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
>                 return false;
>
>         switch (ipi) {
> +       case IPI_CPU_STOP:
> +       case IPI_CPU_CRASH_STOP:
>         case IPI_CPU_BACKTRACE:
>                 return true;
>         default:
> --
> 2.42.0.rc1.204.g551eb34607-goog
>

> -----Original Message----- 
> There's no reason why IPI_CPU_STOP and IPI_CPU_CRASH_STOP can't be
> handled as NMI. They are very simple and everything in them is
> NMI-safe. Mark them as things to use NMI for if NMI is available.
> 
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> I don't actually have any good way to test/validate this patch. It's
> added to the series at Mark's request.

For IPI_CPU_CRASH_STOP, I briefly checked that HARDLOCKUP-ed CPU
(by lkdtm) received the ipi upon crash dump request when pseudo NMI is
enabled.
  Reviewed-by: Misono Tomohiro <misono.tomohiro@fujitsu.com>

Regards,
Tomohiro

> 
> (no changes since v10)
> 
> Changes in v10:
> - ("IPI_CPU_STOP and IPI_CPU_CRASH_STOP should try for NMI") new for
> v10.
> 
>  arch/arm64/kernel/smp.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index c8896cbc5327..4566934aaf9f 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -946,6 +946,8 @@ static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
>  		return false;
> 
>  	switch (ipi) {
> +	case IPI_CPU_STOP:
> +	case IPI_CPU_CRASH_STOP:
>  	case IPI_CPU_BACKTRACE:
>  		return true;
>  	default:
> --
> 2.42.0.rc1.204.g551eb34607-goog
> 
> 
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