linux-kernel - [PATCH RFC 1/1] drivers: firmware: riscv: add unknown NMI support

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Message-Id: <20250919070048.94646-2-cuiyunhui@bytedance.com>
Date: Fri, 19 Sep 2025 15:00:48 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	conor@...nel.org,
	atishp@...osinc.com,
	cleger@...osinc.com,
	ajones@...tanamicro.com,
	apatel@...tanamicro.com,
	cuiyunhui@...edance.com,
	mchitale@...tanamicro.com,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH RFC 1/1] drivers: firmware: riscv: add unknown NMI support

Unknown NMI can force the kernel to respond (e.g., panic) when the
system encounters unrecognized critical hardware events, aiding in
troubleshooting system faults. This is implemented via the Supervisor
Software Events (SSE) framework.

Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
---
 arch/riscv/include/asm/sbi.h     |  1 +
 drivers/firmware/riscv/Kconfig   | 10 +++++
 drivers/firmware/riscv/Makefile  |  1 +
 drivers/firmware/riscv/sse_nmi.c | 77 ++++++++++++++++++++++++++++++++
 4 files changed, 89 insertions(+)
 create mode 100644 drivers/firmware/riscv/sse_nmi.c

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 874cc1d7603a5..5801f90a88f62 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -481,6 +481,7 @@ enum sbi_sse_attr_id {
 
 #define SBI_SSE_EVENT_LOCAL_HIGH_PRIO_RAS	0x00000000
 #define SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP		0x00000001
+#define SBI_SSE_EVENT_LOCAL_UNKNOWN_NMI			0x00000002
 #define SBI_SSE_EVENT_GLOBAL_HIGH_PRIO_RAS	0x00008000
 #define SBI_SSE_EVENT_LOCAL_PMU_OVERFLOW	0x00010000
 #define SBI_SSE_EVENT_LOCAL_LOW_PRIO_RAS	0x00100000
diff --git a/drivers/firmware/riscv/Kconfig b/drivers/firmware/riscv/Kconfig
index ed5b663ac5f91..746bac862ac46 100644
--- a/drivers/firmware/riscv/Kconfig
+++ b/drivers/firmware/riscv/Kconfig
@@ -12,4 +12,14 @@ config RISCV_SBI_SSE
 	  this option provides support to register callbacks on specific SSE
 	  events.
 
+config RISCV_SSE_UNKNOWN_NMI
+	bool "Enable SBI Supervisor Software Events unknown NMI support"
+	depends on RISCV_SBI_SSE
+	default y
+	help
+	  This option enables support for delivering unknown Non-Maskable Interrupt (NMI)
+	  notifications via the Supervisor Software Events (SSE) framework. When enabled,
+	  unknown NMIs can trigger kernel responses (e.g., panic) for unrecognized critical
+	  hardware events, aiding in system fault diagnosis.
+
 endmenu
diff --git a/drivers/firmware/riscv/Makefile b/drivers/firmware/riscv/Makefile
index c8795d4bbb2ea..9242c6cd5e3e9 100644
--- a/drivers/firmware/riscv/Makefile
+++ b/drivers/firmware/riscv/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_RISCV_SBI_SSE)		+= riscv_sbi_sse.o
+obj-$(CONFIG_RISCV_SSE_UNKNOWN_NMI)	+= sse_nmi.o
diff --git a/drivers/firmware/riscv/sse_nmi.c b/drivers/firmware/riscv/sse_nmi.c
new file mode 100644
index 0000000000000..43063f42efff0
--- /dev/null
+++ b/drivers/firmware/riscv/sse_nmi.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <linux/mm.h>
+#include <linux/nmi.h>
+#include <linux/riscv_sbi_sse.h>
+#include <linux/sched/debug.h>
+#include <linux/sysctl.h>
+
+#include <asm/irq_regs.h>
+#include <asm/sbi.h>
+
+int panic_on_unknown_nmi = 1;
+struct sse_event *evt;
+static struct ctl_table_header *unknown_nmi_sysctl_header;
+
+const struct ctl_table unknown_nmi_table[] = {
+	{
+		.procname	= "panic_enable",
+		.data		= &panic_on_unknown_nmi,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+};
+
+static void nmi_handler(struct pt_regs *regs)
+{
+	pr_emerg("NMI received for unknown on CPU %d.\n", smp_processor_id());
+
+	if (panic_on_unknown_nmi)
+		nmi_panic(regs, "NMI: Not continuing");
+
+	pr_emerg("Dazed and confused, but trying to continue\n");
+}
+
+static int nmi_sse_handler(u32 evt, void *arg, struct pt_regs *regs)
+{
+	nmi_handler(regs);
+
+	return 0;
+}
+
+static int sse_nmi_init(void)
+{
+	int ret;
+
+	evt = sse_event_register(SBI_SSE_EVENT_LOCAL_UNKNOWN_NMI, 0,
+				 nmi_sse_handler, NULL);
+	if (IS_ERR(evt))
+		return PTR_ERR(evt);
+
+	ret = sse_event_enable(evt);
+	if (ret) {
+		sse_event_unregister(evt);
+		return ret;
+	}
+
+	unknown_nmi_sysctl_header = register_sysctl("kernel", unknown_nmi_table);
+	if (!unknown_nmi_sysctl_header) {
+		sse_event_disable(evt);
+		sse_event_unregister(evt);
+		return -ENOMEM;
+	}
+
+	pr_info("Using SSE for NMI event delivery\n");
+
+	return 0;
+}
+
+static int __init unknow_nmi_init(void)
+{
+	return sse_nmi_init();
+}
+
+late_initcall(unknow_nmi_init);
-- 
2.39.5