Commit 331a1b3a authored by Douglas Anderson's avatar Douglas Anderson Committed by Catalin Marinas
Browse files

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 8d539b84 ("nmi_backtrace: allow
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: default avatarSumit Garg <sumit.garg@linaro.org>
Signed-off-by: default avatarSumit Garg <sumit.garg@linaro.org>
Co-developed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarStephen Boyd <swboyd@chromium.org>
Reviewed-by: default avatarMisono Tomohiro <misono.tomohiro@fujitsu.com>
Tested-by: default avatarChen-Yu Tsai <wenst@chromium.org>
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20230906090246.v13.4.Ie6c132b96ebbbcddbf6954b9469ed40a6960343c@changeid


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2b2d0a7a

arch/arm64/include/asm/irq.h

+3 −0
Original line number Diff line number Diff line
@@ -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 *));

arch/arm64/kernel/smp.c

+75 −11
Original line number Diff line number Diff line
@@ -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;
@@ -916,9 +960,15 @@ static void ipi_setup(int cpu) 
	if (WARN_ON_ONCE(!ipi_irq_base))

		return;



	for (i = 0; i < nr_ipi; i++)

	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

static void ipi_teardown(int cpu)
@@ -928,24 +978,38 @@ static void ipi_teardown(int cpu) 
	if (WARN_ON_ONCE(!ipi_irq_base))

		return;



	for (i = 0; i < nr_ipi; 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



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;



		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_ON(err);

			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);