Re: [PATCH v7 1/7] arm64: Add framework to turn IPI as NMI

[Masayoshi Mizuma]

On Mon, Nov 02, 2020 at 05:14:41PM +0530, Sumit Garg wrote:
> Introduce framework to turn an IPI as NMI using pseudo NMIs. The main
> motivation for this feature is to have an IPI that can be leveraged to
> invoke NMI functions on other CPUs.
> 
> And current prospective users are NMI backtrace and KGDB CPUs round-up
> whose support is added via future patches.
> 
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/nmi.h | 17 ++++++++++++
>  arch/arm64/kernel/Makefile   |  2 +-
>  arch/arm64/kernel/ipi_nmi.c  | 65 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/nmi.h
>  create mode 100644 arch/arm64/kernel/ipi_nmi.c
> 
> diff --git a/arch/arm64/include/asm/nmi.h b/arch/arm64/include/asm/nmi.h
> new file mode 100644
> index 0000000..4cd14b6
> --- /dev/null
> +++ b/arch/arm64/include/asm/nmi.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_NMI_H
> +#define __ASM_NMI_H
> +
> +#ifndef __ASSEMBLER__
> +
> +#include <linux/cpumask.h>
> +
> +extern bool arm64_supports_nmi(void);
> +extern void arm64_send_nmi(cpumask_t *mask);
> +
> +void set_smp_dynamic_ipi(int ipi);
> +void dynamic_ipi_setup(int cpu);
> +void dynamic_ipi_teardown(int cpu);
> +
> +#endif /* !__ASSEMBLER__ */
> +#endif
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index bbaf0bc..525a1e0 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -17,7 +17,7 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
>  			   return_address.o cpuinfo.o cpu_errata.o		\
>  			   cpufeature.o alternative.o cacheinfo.o		\
>  			   smp.o smp_spin_table.o topology.o smccc-call.o	\
> -			   syscall.o proton-pack.o
> +			   syscall.o proton-pack.o ipi_nmi.o
>  
>  targets			+= efi-entry.o
>  
> diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
> new file mode 100644
> index 0000000..a945dcf
> --- /dev/null
> +++ b/arch/arm64/kernel/ipi_nmi.c
> @@ -0,0 +1,65 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * NMI support for IPIs
> + *
> + * Copyright (C) 2020 Linaro Limited
> + * Author: Sumit Garg <sumit.garg@xxxxxxxxxx>
> + */
> +
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/smp.h>
> +
> +#include <asm/nmi.h>
> +
> +static struct irq_desc *ipi_nmi_desc __read_mostly;
> +static int ipi_nmi_id __read_mostly;
> +
> +bool arm64_supports_nmi(void)
> +{
> +	if (ipi_nmi_desc)
> +		return true;
> +
> +	return false;
> +}
> +
> +void arm64_send_nmi(cpumask_t *mask)
> +{
> +	if (WARN_ON_ONCE(!ipi_nmi_desc))
> +		return;
> +
> +	__ipi_send_mask(ipi_nmi_desc, mask);
> +}
> +
> +static irqreturn_t ipi_nmi_handler(int irq, void *data)
> +{
> +	/* nop, NMI handlers for special features can be added here. */
> +
> +	return IRQ_NONE;
> +}
> +

> +void dynamic_ipi_setup(int cpu)

cpu isn't used here, so void is better?

void dynamic_ipi_setup(void)

> +{
> +	if (!ipi_nmi_desc)
> +		return;
> +
> +	if (!prepare_percpu_nmi(ipi_nmi_id))
> +		enable_percpu_nmi(ipi_nmi_id, IRQ_TYPE_NONE);
> +}
> +

> +void dynamic_ipi_teardown(int cpu)

Same as here:
void dynamic_ipi_teardown(void)

> +{
> +	if (!ipi_nmi_desc)
> +		return;
> +
> +	disable_percpu_nmi(ipi_nmi_id);
> +	teardown_percpu_nmi(ipi_nmi_id);
> +}
> +
> +void __init set_smp_dynamic_ipi(int ipi)
> +{
> +	if (!request_percpu_nmi(ipi, ipi_nmi_handler, "IPI", &cpu_number)) {
> +		ipi_nmi_desc = irq_to_desc(ipi);
> +		ipi_nmi_id = ipi;
> +	}
> +}
> -- 

Otherwise, looks good to me. Please feel free to add:

	Reviewed-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

Thanks,
Masa