[kvm-unit-tests v3 2/2] riscv: Add ISA double trap extension testing
Clément Léger
cleger at rivosinc.com
Mon Jun 16 04:59:00 PDT 2025
This test allows to test the double trap implementation of hardware as
well as the SBI FWFT and SSE support for double trap. The tests will try
to trigger double trap using various sequences and will test to receive
the SSE double trap event if supported.
It is provided as a separate test from the SBI one for two reasons:
- It isn't specifically testing SBI "per se".
- It ends up by trying to crash into in M-mode.
Currently, the test uses a page fault to raise a trap programatically.
Some concern was raised by a github user on the original branch [1]
saying that the spec doesn't mandate any trap to be delegatable and that
we would need a way to detect which ones are delegatable. I think we can
safely assume that PAGE FAULT is delegatable and if a hardware that does
not have support comes up then it will probably be the vendor
responsibility to provide a way to do so.
Link: https://github.com/clementleger/kvm-unit-tests/issues/1 [1]
Signed-off-by: Clément Léger <cleger at rivosinc.com>
---
riscv/Makefile | 1 +
lib/riscv/asm/csr.h | 1 +
lib/riscv/asm/processor.h | 10 ++
riscv/isa-dbltrp.c | 210 ++++++++++++++++++++++++++++++++++++++
riscv/unittests.cfg | 4 +
5 files changed, 226 insertions(+)
create mode 100644 riscv/isa-dbltrp.c
diff --git a/riscv/Makefile b/riscv/Makefile
index 11e68eae..d71c9d2e 100644
--- a/riscv/Makefile
+++ b/riscv/Makefile
@@ -14,6 +14,7 @@ tests =
tests += $(TEST_DIR)/sbi.$(exe)
tests += $(TEST_DIR)/selftest.$(exe)
tests += $(TEST_DIR)/sieve.$(exe)
+tests += $(TEST_DIR)/isa-dbltrp.$(exe)
all: $(tests)
diff --git a/lib/riscv/asm/csr.h b/lib/riscv/asm/csr.h
index 3e4b5fca..6a8e0578 100644
--- a/lib/riscv/asm/csr.h
+++ b/lib/riscv/asm/csr.h
@@ -18,6 +18,7 @@
#define SR_SIE _AC(0x00000002, UL)
#define SR_SPP _AC(0x00000100, UL)
+#define SR_SDT _AC(0x01000000, UL) /* Supervisor Double Trap */
/* Exception cause high bit - is an interrupt if set */
#define CAUSE_IRQ_FLAG (_AC(1, UL) << (__riscv_xlen - 1))
diff --git a/lib/riscv/asm/processor.h b/lib/riscv/asm/processor.h
index 631ce226..a3dab064 100644
--- a/lib/riscv/asm/processor.h
+++ b/lib/riscv/asm/processor.h
@@ -50,6 +50,16 @@ static inline void ipi_ack(void)
csr_clear(CSR_SIP, IE_SSIE);
}
+static inline void local_dlbtrp_enable(void)
+{
+ csr_set(CSR_SSTATUS, SR_SDT);
+}
+
+static inline void local_dlbtrp_disable(void)
+{
+ csr_clear(CSR_SSTATUS, SR_SDT);
+}
+
void install_exception_handler(unsigned long cause, void (*handler)(struct pt_regs *));
void install_irq_handler(unsigned long cause, void (*handler)(struct pt_regs *));
void do_handle_exception(struct pt_regs *regs);
diff --git a/riscv/isa-dbltrp.c b/riscv/isa-dbltrp.c
new file mode 100644
index 00000000..dcfa66da
--- /dev/null
+++ b/riscv/isa-dbltrp.c
@@ -0,0 +1,210 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * SBI verification
+ *
+ * Copyright (C) 2025, Rivos Inc., Clément Léger <cleger at rivosinc.com>
+ */
+#include <alloc.h>
+#include <alloc_page.h>
+#include <libcflat.h>
+#include <stdlib.h>
+
+#include <asm/csr.h>
+#include <asm/page.h>
+#include <asm/processor.h>
+#include <asm/ptrace.h>
+#include <asm/sbi.h>
+
+#include <sbi-tests.h>
+
+static bool double_trap;
+static bool clear_sdt;
+
+#define INSN_LEN(insn) ((((insn) & 0x3) < 0x3) ? 2 : 4)
+
+#define GEN_TRAP() \
+do { \
+ void *ptr = NULL; \
+ unsigned long value = 0; \
+ asm volatile( \
+ " .option push\n" \
+ " .option arch,-c\n" \
+ " sw %0, 0(%1)\n" \
+ " .option pop\n" \
+ : : "r" (value), "r" (ptr) : "memory"); \
+} while (0)
+
+static void pagefault_trap_handler(struct pt_regs *regs)
+{
+ if (READ_ONCE(clear_sdt))
+ local_dlbtrp_disable();
+
+ if (READ_ONCE(double_trap)) {
+ WRITE_ONCE(double_trap, false);
+ GEN_TRAP();
+ }
+
+ /* Skip trapping instruction */
+ regs->epc += 4;
+
+ local_dlbtrp_enable();
+}
+
+static bool sse_dbltrp_called;
+
+static void sse_dbltrp_handler(void *data, struct pt_regs *regs, unsigned int hartid)
+{
+ struct sbiret ret;
+ unsigned long flags;
+ unsigned long expected_flags = SBI_SSE_ATTR_INTERRUPTED_FLAGS_SSTATUS_SPP |
+ SBI_SSE_ATTR_INTERRUPTED_FLAGS_SSTATUS_SDT;
+
+ ret = sbi_sse_read_attrs(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP, SBI_SSE_ATTR_INTERRUPTED_FLAGS, 1,
+ &flags);
+ sbiret_report_error(&ret, SBI_SUCCESS, "Get double trap event flags");
+ report(flags == expected_flags, "SSE flags == 0x%lx", expected_flags);
+
+ WRITE_ONCE(sse_dbltrp_called, true);
+
+ /* Skip trapping instruction */
+ regs->epc += 4;
+}
+
+static int sse_double_trap(void)
+{
+ struct sbiret ret;
+ int err = 0;
+
+ struct sbi_sse_handler_arg handler_arg = {
+ .handler = sse_dbltrp_handler,
+ .stack = alloc_page() + PAGE_SIZE,
+ };
+
+ report_prefix_push("sse");
+
+ ret = sbi_sse_hart_unmask();
+ if (!sbiret_report_error(&ret, SBI_SUCCESS, "SSE hart unmask ok")) {
+ report_skip("Failed to unmask SSE events, skipping test");
+ goto out_free_page;
+ }
+
+ ret = sbi_sse_register(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP, &handler_arg);
+ if (ret.error == SBI_ERR_NOT_SUPPORTED) {
+ report_skip("SSE double trap event is not supported");
+ goto out_mask_sse;
+ }
+ sbiret_report_error(&ret, SBI_SUCCESS, "SSE double trap register");
+
+ ret = sbi_sse_enable(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP);
+ if (!sbiret_report_error(&ret, SBI_SUCCESS, "SSE double trap enable"))
+ goto out_unregister;
+
+ /*
+ * Generate a double crash so that an SSE event should be generated. The SPEC (ISA nor SBI)
+ * does not explicitly tell that if supported it should generate an SSE event but that's
+ * a reasonable assumption to do so if both FWFT and SSE are supported.
+ */
+ WRITE_ONCE(clear_sdt, false);
+ WRITE_ONCE(double_trap, true);
+ GEN_TRAP();
+
+ report(READ_ONCE(sse_dbltrp_called), "SSE double trap event generated");
+
+ ret = sbi_sse_disable(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP);
+ sbiret_report_error(&ret, SBI_SUCCESS, "SSE double trap disable");
+
+out_unregister:
+ ret = sbi_sse_unregister(SBI_SSE_EVENT_LOCAL_DOUBLE_TRAP);
+ if (!sbiret_report_error(&ret, SBI_SUCCESS, "SSE double trap unregister"))
+ err = ret.error;
+
+out_mask_sse:
+ sbi_sse_hart_mask();
+
+out_free_page:
+ free_page(handler_arg.stack - PAGE_SIZE);
+ report_prefix_pop();
+
+ return err;
+}
+
+static void check_double_trap(void)
+{
+ struct sbiret ret;
+
+ /* Disable double trap */
+ ret = sbi_fwft_set(SBI_FWFT_DOUBLE_TRAP, 0, 0);
+ sbiret_report_error(&ret, SBI_SUCCESS, "Set double trap enable feature value == 0");
+ ret = sbi_fwft_get(SBI_FWFT_DOUBLE_TRAP);
+ sbiret_report(&ret, SBI_SUCCESS, 0, "Get double trap enable feature value == 0");
+
+ install_exception_handler(EXC_STORE_PAGE_FAULT, pagefault_trap_handler);
+
+ WRITE_ONCE(clear_sdt, true);
+ WRITE_ONCE(double_trap, true);
+ GEN_TRAP();
+ report_pass("Double trap disabled, trap first time ok");
+
+ /* Enable double trap */
+ ret = sbi_fwft_set(SBI_FWFT_DOUBLE_TRAP, 1, 0);
+ sbiret_report_error(&ret, SBI_SUCCESS, "Set double trap enable feature value == 1");
+ ret = sbi_fwft_get(SBI_FWFT_DOUBLE_TRAP);
+ if (!sbiret_report(&ret, SBI_SUCCESS, 1, "Get double trap enable feature value == 1"))
+ return;
+
+ /* First time, clear the double trap flag (SDT) so that it doesn't generate a double trap */
+ WRITE_ONCE(clear_sdt, true);
+ WRITE_ONCE(double_trap, true);
+
+ GEN_TRAP();
+ report_pass("Trapped twice allowed ok");
+
+ if (sbi_probe(SBI_EXT_SSE)) {
+ if (sse_double_trap()) {
+ report_skip("Could not correctly unregister SSE event, skipping last test");
+ return;
+ }
+ } else {
+ report_skip("SSE double trap event will not be tested, extension is not available");
+ }
+
+ if (!env_or_skip("DOUBLE_TRAP_TEST_CRASH"))
+ return;
+
+ /*
+ * Third time, keep the double trap flag (SDT) and generate another trap, this should
+ * generate a double trap. Since there is no SSE handler registered, it should crash to
+ * M-mode.
+ */
+ WRITE_ONCE(clear_sdt, false);
+ WRITE_ONCE(double_trap, true);
+ report_info("Should generate a double trap and crash!");
+ GEN_TRAP();
+ report_fail("Should have crashed!");
+}
+
+int main(int argc, char **argv)
+{
+ struct sbiret ret;
+
+ report_prefix_push("dbltrp");
+
+ if (!sbi_probe(SBI_EXT_FWFT)) {
+ report_skip("FWFT extension is not available, can not enable double traps");
+ goto out;
+ }
+
+ ret = sbi_fwft_get(SBI_FWFT_DOUBLE_TRAP);
+ if (ret.error == SBI_ERR_NOT_SUPPORTED) {
+ report_skip("SBI_FWFT_DOUBLE_TRAP is not supported!");
+ goto out;
+ }
+
+ if (sbiret_report_error(&ret, SBI_SUCCESS, "SBI_FWFT_DOUBLE_TRAP get value"))
+ check_double_trap();
+
+out:
+ report_prefix_pop();
+
+ return report_summary();
+}
diff --git a/riscv/unittests.cfg b/riscv/unittests.cfg
index 2eb760ec..286e1cc7 100644
--- a/riscv/unittests.cfg
+++ b/riscv/unittests.cfg
@@ -18,3 +18,7 @@ groups = selftest
file = sbi.flat
smp = $MAX_SMP
groups = sbi
+
+[dbltrp]
+file = isa-dbltrp.flat
+groups = isa sbi
--
2.49.0
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