[PATCH v11 4/6] arm64: smp: Add arch support for backtrace using pseudo-NMI
Tomohiro Misono (Fujitsu)
misono.tomohiro at fujitsu.com
Mon Aug 28 22:23:34 PDT 2023
> -----Original Message-----
> Subject: [PATCH v11 4/6] arm64: smp: Add arch support for backtrace using
> pseudo-NMI
>
> Enable arch_trigger_cpumask_backtrace() support on arm64. This enables
> things much like they are enabled on arm32 (including some of the
> funky logic around NR_IPI, nr_ipi, and MAX_IPI) but with the
> difference that, unlike arm32, we'll try to enable the backtrace to
> use pseudo-NMI.
>
> NOTE: this patch is a squash of the little bit of code adding the
> ability to mark an IPI to try to use pseudo-NMI plus the little bit of
> code to hook things up for kgdb. This approach was decided upon in the
> discussion of v9 [1].
>
> This patch depends on commit 36759e343ff9 ("nmi_backtrace: allow
Hi,
Is this commit ID valid? I believe this commit is not included in the
mainline yet. Other than this,
Reviewed-by: Misono Tomohiro <misono.tomohiro at fujitsu.com>
Regards,
Tomohiro
> excluding an arbitrary CPU") since that commit changed the prototype
> of arch_trigger_cpumask_backtrace(), which this patch implements.
>
> [1] https://lore.kernel.org/r/ZORY51mF4alI41G1@FVFF77S0Q05N
>
> Co-developed-by: Sumit Garg <sumit.garg at linaro.org>
> Signed-off-by: Sumit Garg <sumit.garg at linaro.org>
> Co-developed-by: Mark Rutland <mark.rutland at arm.com>
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Signed-off-by: Douglas Anderson <dianders at chromium.org>
> ---
>
> Changes in v11:
> - Adjust comment about NR_IPI/MAX_IPI.
> - Don't use confusing "backed by" idiom in comment.
> - Made arm64_backtrace_ipi() static.
>
> Changes in v10:
> - Backtrace now directly supported in smp.c
> - Squash backtrace into patch adding support for pseudo-NMI IPIs.
>
> Changes in v9:
> - Added comments that we might not be using NMI always.
> - Fold in v8 patch #10 ("Fallback to a regular IPI if NMI isn't enabled")
> - Moved header file out of "include" since it didn't need to be there.
> - Remove arm64_supports_nmi()
> - Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.
> - arch_trigger_cpumask_backtrace() no longer returns bool
>
> Changes in v8:
> - Removed "#ifdef CONFIG_SMP" since arm64 is always SMP
> - debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param
>
> arch/arm64/include/asm/irq.h | 3 ++
> arch/arm64/kernel/smp.c | 86
> +++++++++++++++++++++++++++++++-----
> 2 files changed, 78 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
> index fac08e18bcd5..50ce8b697ff3 100644
> --- a/arch/arm64/include/asm/irq.h
> +++ b/arch/arm64/include/asm/irq.h
> @@ -6,6 +6,9 @@
>
> #include <asm-generic/irq.h>
>
> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int
> exclude_cpu);
> +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
> +
> struct pt_regs;
>
> int set_handle_irq(void (*handle_irq)(struct pt_regs *));
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index a5848f1ef817..c8896cbc5327 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -33,6 +33,7 @@
> #include <linux/kernel_stat.h>
> #include <linux/kexec.h>
> #include <linux/kvm_host.h>
> +#include <linux/nmi.h>
>
> #include <asm/alternative.h>
> #include <asm/atomic.h>
> @@ -72,12 +73,18 @@ enum ipi_msg_type {
> IPI_CPU_CRASH_STOP,
> IPI_TIMER,
> IPI_IRQ_WORK,
> - NR_IPI
> + NR_IPI,
> + /*
> + * Any enum >= NR_IPI and < MAX_IPI is special and not tracable
> + * with trace_ipi_*
> + */
> + IPI_CPU_BACKTRACE = NR_IPI,
> + MAX_IPI
> };
>
> static int ipi_irq_base __read_mostly;
> static int nr_ipi __read_mostly = NR_IPI;
> -static struct irq_desc *ipi_desc[NR_IPI] __read_mostly;
> +static struct irq_desc *ipi_desc[MAX_IPI] __read_mostly;
>
> static void ipi_setup(int cpu);
>
> @@ -845,6 +852,22 @@ static void __noreturn ipi_cpu_crash_stop(unsigned int
> cpu, struct pt_regs *regs
> #endif
> }
>
> +static void arm64_backtrace_ipi(cpumask_t *mask)
> +{
> + __ipi_send_mask(ipi_desc[IPI_CPU_BACKTRACE], mask);
> +}
> +
> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int
> exclude_cpu)
> +{
> + /*
> + * NOTE: though nmi_trigger_cpumask_backtrace has "nmi_" in the
> name,
> + * nothing about it truly needs to be implemented using an NMI, it's
> + * just that it's _allowed_ to work with NMIs. If ipi_should_be_nmi()
> + * returned false our backtrace attempt will just use a regular IPI.
> + */
> + nmi_trigger_cpumask_backtrace(mask, exclude_cpu,
> arm64_backtrace_ipi);
> +}
> +
> /*
> * Main handler for inter-processor interrupts
> */
> @@ -888,6 +911,14 @@ static void do_handle_IPI(int ipinr)
> break;
> #endif
>
> + case IPI_CPU_BACKTRACE:
> + /*
> + * NOTE: in some cases this _won't_ be NMI context. See the
> + * comment in arch_trigger_cpumask_backtrace().
> + */
> + nmi_cpu_backtrace(get_irq_regs());
> + break;
> +
> default:
> pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
> break;
> @@ -909,6 +940,19 @@ static void smp_cross_call(const struct cpumask *target,
> unsigned int ipinr)
> __ipi_send_mask(ipi_desc[ipinr], target);
> }
>
> +static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
> +{
> + if (!system_uses_irq_prio_masking())
> + return false;
> +
> + switch (ipi) {
> + case IPI_CPU_BACKTRACE:
> + return true;
> + default:
> + return false;
> + }
> +}
> +
> static void ipi_setup(int cpu)
> {
> int i;
> @@ -916,8 +960,14 @@ static void ipi_setup(int cpu)
> if (WARN_ON_ONCE(!ipi_irq_base))
> return;
>
> - for (i = 0; i < nr_ipi; i++)
> - enable_percpu_irq(ipi_irq_base + i, 0);
> + for (i = 0; i < nr_ipi; i++) {
> + if (ipi_should_be_nmi(i)) {
> + prepare_percpu_nmi(ipi_irq_base + i);
> + enable_percpu_nmi(ipi_irq_base + i, 0);
> + } else {
> + enable_percpu_irq(ipi_irq_base + i, 0);
> + }
> + }
> }
>
> #ifdef CONFIG_HOTPLUG_CPU
> @@ -928,8 +978,14 @@ static void ipi_teardown(int cpu)
> if (WARN_ON_ONCE(!ipi_irq_base))
> return;
>
> - for (i = 0; i < nr_ipi; i++)
> - disable_percpu_irq(ipi_irq_base + i);
> + for (i = 0; i < nr_ipi; i++) {
> + if (ipi_should_be_nmi(i)) {
> + disable_percpu_nmi(ipi_irq_base + i);
> + teardown_percpu_nmi(ipi_irq_base + i);
> + } else {
> + disable_percpu_irq(ipi_irq_base + i);
> + }
> + }
> }
> #endif
>
> @@ -937,15 +993,23 @@ void __init set_smp_ipi_range(int ipi_base, int n)
> {
> int i;
>
> - WARN_ON(n < NR_IPI);
> - nr_ipi = min(n, NR_IPI);
> + WARN_ON(n < MAX_IPI);
> + nr_ipi = min(n, MAX_IPI);
>
> for (i = 0; i < nr_ipi; i++) {
> int err;
>
> - err = request_percpu_irq(ipi_base + i, ipi_handler,
> - "IPI", &cpu_number);
> - WARN_ON(err);
> + if (ipi_should_be_nmi(i)) {
> + err = request_percpu_nmi(ipi_base + i, ipi_handler,
> + "IPI", &cpu_number);
> + WARN(err, "Could not request IPI %d as NMI,
> err=%d\n",
> + i, err);
> + } else {
> + err = request_percpu_irq(ipi_base + i, ipi_handler,
> + "IPI", &cpu_number);
> + WARN(err, "Could not request IPI %d as IRQ,
> err=%d\n",
> + i, err);
> + }
>
> ipi_desc[i] = irq_to_desc(ipi_base + i);
> irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
> --
> 2.42.0.rc1.204.g551eb34607-goog
>
>
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