2020-11-02 11:49:10

by Sumit Garg

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

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 <[email protected]>
---
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()))
+ 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

2021-06-25 14:55:03

by Chen-Yu Tsai

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

Hi,

On Mon, Nov 2, 2020 at 7:47 PM Sumit Garg <[email protected]> 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 <[email protected]>
> ---
> 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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