Re: [PATCH 2/3] KVM: riscv: selftests: Decode stval to identify exact exception type

From: Atish Patra <atish.patra@linux.dev>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: Anup Patel <anup@brainfault.org>,
	Atish Patra <atishp@atishpatra.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alexandre Ghiti <alex@ghiti.fr>,
	kvm@vger.kernel.org, kvm-riscv@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] KVM: riscv: selftests: Decode stval to identify exact exception type
Date: Mon, 28 Apr 2025 15:48:37 -0700	[thread overview]
Message-ID: <7f84de30-80db-492a-adde-1f29d69da240@linux.dev> (raw)
In-Reply-To: <20250425-f458b9801a83cc35bda55c74@orel>

On 4/25/25 6:33 AM, Andrew Jones wrote:
> On Mon, Mar 24, 2025 at 05:40:30PM -0700, Atish Patra wrote:
>> Currently, the sbi_pmu_test continues if the exception type is illegal
>> instruction because access to hpmcounter will generate that. However, we
>> may get illegal for other reasons as well 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.
>>
>> Signed-off-by: Atish Patra <atishp@rivosinc.com>
>> ---
>>   tools/testing/selftests/kvm/riscv/sbi_pmu_test.c | 32 ++++++++++++++++++++++++
>>   1 file changed, 32 insertions(+)
>>
>> diff --git a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> index 03406de4989d..11bde69b5238 100644
>> --- a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> +++ b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> @@ -128,11 +128,43 @@ static void stop_counter(unsigned long counter, unsigned long stop_flags)
>>   		       "Unable to stop counter %ld error %ld\n", counter, ret.error);
>>   }
>>   
>> +#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)
> It'd be good to put these macros in include/riscv/processor.h or some new
> include/riscv/ header to be shared with other tests that may want to
> decode stval.

Sure. I will move it to include/riscv/processor.h

> Thanks,
> drew
>
>> +
>>   static void guest_illegal_exception_handler(struct ex_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->stval;
>> +	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,
>> +		       "Unexpected csr_num 0x%x\n", csr_num);
>> +
>>   	illegal_handler_invoked = true;
>>   	/* skip the trapping instruction */
>>   	regs->epc += 4;
>>
>> -- 
>> 2.43.0
>>
>>
>> -- 
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>> kvm-riscv@lists.infradead.org
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