linux-kernel - [PATCH v2 2/3] KVM: riscv: selftests: Decode stval to identify exact exception type

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Message-Id: <20250429-kvm_selftest_improve-v2-2-51713f91e04a@rivosinc.com>
Date: Tue, 29 Apr 2025 17:18:46 -0700
From: Atish Patra <atishp@...osinc.com>
To: Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>, 
 Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>, 
 Andrew Jones <ajones@...tanamicro.com>
Cc: kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
 linux-riscv@...ts.infradead.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Atish Patra <atishp@...osinc.com>
Subject: [PATCH v2 2/3] KVM: riscv: selftests: Decode stval to identify
 exact exception type

Currently, the sbi_pmu_test continues if the exception type is illegal
instruction because access to hpmcounter will generate that. However
illegal instruction exception may occur due to the other reasons
which should result in test assertion.

Use the stval to decode the exact type of instructions and which csrs are
being accessed if it is csr access instructions. Assert in all cases
except if it is a csr access instructions that access valid PMU related
registers.

Reviewed-by: Anup Patel <anup@...infault.org>
Signed-off-by: Atish Patra <atishp@...osinc.com>
---
 .../testing/selftests/kvm/include/riscv/processor.h  | 13 +++++++++++++
 tools/testing/selftests/kvm/riscv/sbi_pmu_test.c     | 20 ++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/riscv/processor.h b/tools/testing/selftests/kvm/include/riscv/processor.h
index 1b5aef87de0f..162f303d9daa 100644
--- a/tools/testing/selftests/kvm/include/riscv/processor.h
+++ b/tools/testing/selftests/kvm/include/riscv/processor.h
@@ -11,6 +11,19 @@
 #include <asm/csr.h>
 #include "kvm_util.h"
 
+#define INSN_OPCODE_MASK	0x007c
+#define INSN_OPCODE_SHIFT	2
+#define INSN_OPCODE_SYSTEM	28
+
+#define INSN_MASK_FUNCT3	0x7000
+#define INSN_SHIFT_FUNCT3	12
+
+#define INSN_CSR_MASK		0xfff00000
+#define INSN_CSR_SHIFT		20
+
+#define GET_RM(insn)            (((insn) & INSN_MASK_FUNCT3) >> INSN_SHIFT_FUNCT3)
+#define GET_CSR_NUM(insn)       (((insn) & INSN_CSR_MASK) >> INSN_CSR_SHIFT)
+
 static inline uint64_t __kvm_reg_id(uint64_t type, uint64_t subtype,
 				    uint64_t idx, uint64_t size)
 {
diff --git a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
index 6e66833e5941..3c47268df262 100644
--- a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
+++ b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
@@ -130,9 +130,29 @@ static void stop_counter(unsigned long counter, unsigned long stop_flags)
 
 static void guest_illegal_exception_handler(struct pt_regs *regs)
 {
+	unsigned long insn;
+	int opcode, csr_num, funct3;
+
 	__GUEST_ASSERT(regs->cause == EXC_INST_ILLEGAL,
 		       "Unexpected exception handler %lx\n", regs->cause);
 
+	insn = regs->badaddr;
+	opcode = (insn & INSN_OPCODE_MASK) >> INSN_OPCODE_SHIFT;
+	__GUEST_ASSERT(opcode == INSN_OPCODE_SYSTEM,
+		       "Unexpected instruction with opcode 0x%x insn 0x%lx\n", opcode, insn);
+
+	csr_num = GET_CSR_NUM(insn);
+	funct3 = GET_RM(insn);
+	/* Validate if it is a CSR read/write operation */
+	__GUEST_ASSERT(funct3 <= 7 && (funct3 != 0 && funct3 != 4),
+		       "Unexpected system opcode with funct3 0x%x csr_num 0x%x\n",
+		       funct3, csr_num);
+
+	/* Validate if it is a HPMCOUNTER CSR operation */
+	__GUEST_ASSERT((csr_num >= CSR_CYCLE && csr_num <= CSR_HPMCOUNTER31) ||
+		       (csr_num >= CSR_CYCLEH && csr_num <= CSR_HPMCOUNTER31H),
+		       "Unexpected csr_num 0x%x\n", csr_num);
+
 	illegal_handler_invoked = true;
 	/* skip the trapping instruction */
 	regs->epc += 4;

-- 
2.43.0