[RFC v2 1/2] riscv: allow resume after exception

[Heinrich Schuchardt]

If CSRs like seed are readable by S-mode, may not be determinable by
S-mode. For safe driver probing allow to resume via a longjmp after an
exception.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
v2:
	new patch
---
 arch/riscv/lib/interrupts.c | 13 +++++++++++++
 include/interrupt.h         | 22 ++++++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 include/interrupt.h

diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index 02dbcfd423..a26ccc721f 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -12,6 +12,7 @@
 #include <linux/compat.h>
 #include <efi_loader.h>
 #include <hang.h>
+#include <interrupt.h>
 #include <irq_func.h>
 #include <asm/global_data.h>
 #include <asm/ptrace.h>
@@ -21,6 +22,13 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+static struct resume_data *resume;
+
+void set_resume(struct resume_data *data)
+{
+	resume = data;
+}
+
 static void show_efi_loaded_images(uintptr_t epc)
 {
 	efi_print_image_infos((void *)epc);
@@ -105,6 +113,11 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
 		"Store/AMO page fault",
 	};
 
+	if (resume) {
+		resume->code = code;
+		longjmp(resume->jump, 1);
+	}
+
 	if (code < ARRAY_SIZE(exception_code))
 		printf("Unhandled exception: %s\n", exception_code[code]);
 	else
diff --git a/include/interrupt.h b/include/interrupt.h
new file mode 100644
index 0000000000..1baa60bcf2
--- /dev/null
+++ b/include/interrupt.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <asm/setjmp.h>
+
+/**
+ * struct resume_data - data for resume after interrupt
+ */
+struct resume_data {
+	/** @jump: longjmp buffer */
+	jmp_buf jump;
+	/** @code: exception code */
+	ulong code;
+};
+
+/**
+ * set_resume() - set longjmp buffer for resuming after interrupt
+ *
+ * When resuming the exception code will be returned in @data->code.
+ *
+ * @data:	pointer to structure with longjmp address
+ */
+void set_resume(struct resume_data *data);
-- 
2.40.1