linux-kernel - [PATCH v2 8/8] drivers: firmware: riscv: add unknown nmi support

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Message-Id: <20251118025015.42491-9-cuiyunhui@bytedance.com>
Date: Tue, 18 Nov 2025 10:50:15 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: conor@...nel.org,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	cuiyunhui@...edance.com,
	luxu.kernel@...edance.com,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	jassisinghbrar@...il.com,
	conor.dooley@...rochip.com,
	valentina.fernandezalanis@...rochip.com,
	catalin.marinas@....com,
	will@...nel.org,
	maz@...nel.org,
	timothy.hayes@....com,
	lpieralisi@...nel.org,
	arnd@...db.de,
	kees@...nel.org,
	tglx@...utronix.de,
	viresh.kumar@...aro.org,
	boqun.feng@...il.com,
	linux-arm-kernel@...ts.infradead.org,
	cleger@...osinc.com,
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Subject: [PATCH v2 8/8] drivers: firmware: riscv: add unknown nmi support

Register unknown_nmi_handler() as the handler for the UNKNOWN_NMI
event. When the system becomes unresponsive, unknown_nmi_handler()
can be manually triggered, which in turn invokes nmi_panic() to
collect vmcore for root cause analysis.

Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
---
 arch/riscv/include/asm/sbi.h           |  1 +
 drivers/firmware/riscv/riscv_sse_nmi.c | 68 ++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 874cc1d7603a5..52d3fdf2d4cc1 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -486,6 +486,7 @@ enum sbi_sse_attr_id {
 #define SBI_SSE_EVENT_LOCAL_LOW_PRIO_RAS	0x00100000
 #define SBI_SSE_EVENT_GLOBAL_LOW_PRIO_RAS	0x00108000
 #define SBI_SSE_EVENT_LOCAL_SOFTWARE_INJECTED	0xffff0000
+#define SBI_SSE_EVENT_LOCAL_UNKNOWN_NMI		0xffff0001
 #define SBI_SSE_EVENT_GLOBAL_SOFTWARE_INJECTED	0xffff8000
 
 #define SBI_SSE_EVENT_PLATFORM		BIT(14)
diff --git a/drivers/firmware/riscv/riscv_sse_nmi.c b/drivers/firmware/riscv/riscv_sse_nmi.c
index 5035d4ec485f6..e895abf583bd5 100644
--- a/drivers/firmware/riscv/riscv_sse_nmi.c
+++ b/drivers/firmware/riscv/riscv_sse_nmi.c
@@ -7,6 +7,7 @@
 #include <linux/nmi.h>
 #include <linux/riscv_sbi_sse.h>
 #include <linux/riscv_sse_nmi.h>
+#include <linux/sysctl.h>
 
 #include <asm/irq_regs.h>
 #include <asm/sbi.h>
@@ -16,7 +17,10 @@
 	do { if (type & (mask)) func(__VA_ARGS__); } while (0)
 
 bool nmi_available;
+static int unknown_nmi_panic;
 static struct sse_event *local_nmi_evt;
+static struct sse_event *unknown_nmi_evt;
+static struct ctl_table_header *unknown_nmi_sysctl_header;
 static atomic_t local_nmi_arg = ATOMIC_INIT(LOCAL_NMI_NONE);
 
 bool nmi_support(void)
@@ -51,6 +55,35 @@ void send_nmi_mask(cpumask_t *mask, enum local_nmi_type type)
 		send_nmi_single(cpu, type);
 }
 
+static int __init setup_unknown_nmi_panic(char *str)
+{
+	unknown_nmi_panic = 1;
+	return 1;
+}
+__setup("unknown_nmi_panic", setup_unknown_nmi_panic);
+
+static const struct ctl_table unknown_nmi_table[] = {
+	{
+		.procname       = "unknown_nmi_panic",
+		.data           = &unknown_nmi_panic,
+		.maxlen         = sizeof(bool),
+		.mode           = 0644,
+		.proc_handler   = proc_dobool,
+	},
+};
+
+static int unknown_nmi_handler(u32 evt, void *arg, struct pt_regs *regs)
+{
+	pr_emerg("NMI received for unknown on CPU %d.\n", smp_processor_id());
+
+	if (unknown_nmi_panic)
+		nmi_panic(regs, "NMI: Not continuing");
+
+	pr_emerg("Dazed and confused, but trying to continue\n");
+
+	return 0;
+}
+
 static int local_nmi_handler(u32 evt, void *arg, struct pt_regs *regs)
 {
 	enum local_nmi_type type = atomic_read((atomic_t *)arg);
@@ -66,6 +99,35 @@ static int local_nmi_handler(u32 evt, void *arg, struct pt_regs *regs)
 	return 0;
 }
 
+static int unknown_nmi_init(void)
+{
+	int ret;
+
+	unknown_nmi_evt = sse_event_register(SBI_SSE_EVENT_LOCAL_UNKNOWN_NMI, 0,
+					     unknown_nmi_handler, NULL);
+	if (IS_ERR(unknown_nmi_evt))
+		return PTR_ERR(unknown_nmi_evt);
+
+	ret = sse_event_enable(unknown_nmi_evt);
+	if (ret)
+		goto err_unregister;
+
+	unknown_nmi_sysctl_header = register_sysctl("kernel", unknown_nmi_table);
+	if (!unknown_nmi_sysctl_header) {
+		ret = -ENOMEM;
+		goto err_disable;
+	}
+
+	pr_info("Using SSE for unknown NMI event delivery\n");
+	return 0;
+
+err_disable:
+	sse_event_disable(unknown_nmi_evt);
+err_unregister:
+	sse_event_unregister(unknown_nmi_evt);
+	return ret;
+}
+
 static int __init local_nmi_init(void)
 {
 	int ret;
@@ -98,6 +160,12 @@ static int __init sse_nmi_init(void)
 
 	WRITE_ONCE(nmi_available, true);
 
+	ret = unknown_nmi_init();
+	if (ret) {
+		pr_err("Unknown_nmi_init failed with error %d\n", ret);
+		return ret;
+	}
+
 	return 0;
 }
 
-- 
2.39.5