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

On Mon, 2 Nov 2020 at 21:03, Masayoshi Mizuma [off-list ref] wrote:

On Mon, Nov 02, 2020 at 05:14:41PM +0530, Sumit Garg wrote:

quoted

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 <redacted>
---
 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@linaro.org>
+ */
+
+#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;
+}
+

quoted

+void dynamic_ipi_setup(int cpu)

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

void dynamic_ipi_setup(void)

Ack.

quoted

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

quoted

+void dynamic_ipi_teardown(int cpu)

Same as here:
void dynamic_ipi_teardown(void)

Ack.

quoted

+{
+     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 [off-list ref]

Thanks.

-Sumit

Thanks,
Masa

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