Re: [PATCH v7 7/7] arm64: kgdb: Roundup cpus using IPI as NMI

[Chen-Yu Tsai]

Hi,

On Mon, Nov 2, 2020 at 7:47 PM Sumit Garg <sumit.garg@xxxxxxxxxx> wrote:
>
> arm64 platforms with GICv3 or later supports pseudo NMIs which can be
> leveraged to roundup CPUs which are stuck in hard lockup state with
> interrupts disabled that wouldn't be possible with a normal IPI.
>
> So instead switch to roundup CPUs using IPI turned as NMI. And in
> case a particular arm64 platform doesn't supports pseudo NMIs,
> it will switch back to default kgdb CPUs roundup mechanism.
>
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/ipi_nmi.c |  5 +++++
>  arch/arm64/kernel/kgdb.c    | 18 ++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
> index 597dcf7..898d69c 100644
> --- a/arch/arm64/kernel/ipi_nmi.c
> +++ b/arch/arm64/kernel/ipi_nmi.c
> @@ -8,6 +8,7 @@
>
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
> +#include <linux/kgdb.h>
>  #include <linux/nmi.h>
>  #include <linux/smp.h>
>
> @@ -45,10 +46,14 @@ bool arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
>  static irqreturn_t ipi_nmi_handler(int irq, void *data)
>  {
>         irqreturn_t ret = IRQ_NONE;
> +       unsigned int cpu = smp_processor_id();
>
>         if (nmi_cpu_backtrace(get_irq_regs()))
>                 ret = IRQ_HANDLED;
>
> +       if (!kgdb_nmicallback(cpu, get_irq_regs()))

This fails to compile if CONFIG_KGDB isn't enabled.


ChenYu


> +               ret = IRQ_HANDLED;
> +
>         return ret;
>  }
>
> diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
> index 1a157ca3..371b176 100644
> --- a/arch/arm64/kernel/kgdb.c
> +++ b/arch/arm64/kernel/kgdb.c
> @@ -17,6 +17,7 @@
>
>  #include <asm/debug-monitors.h>
>  #include <asm/insn.h>
> +#include <asm/nmi.h>
>  #include <asm/traps.h>
>
>  struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
> @@ -353,3 +354,20 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
>         return aarch64_insn_write((void *)bpt->bpt_addr,
>                         *(u32 *)bpt->saved_instr);
>  }
> +
> +void kgdb_roundup_cpus(void)
> +{
> +       struct cpumask mask;
> +
> +       if (!arm64_supports_nmi()) {
> +               kgdb_smp_call_nmi_hook();
> +               return;
> +       }
> +
> +       cpumask_copy(&mask, cpu_online_mask);
> +       cpumask_clear_cpu(raw_smp_processor_id(), &mask);
> +       if (cpumask_empty(&mask))
> +               return;
> +
> +       arm64_send_nmi(&mask);
> +}
> --
> 2.7.4
>
>
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