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

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Message-ID: <20250430-b40cd14818cc9264506e61f2@orel>
Date: Wed, 30 Apr 2025 09:09:00 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Atish Patra <atishp@...osinc.com>
Cc: 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>, kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] KVM: riscv: selftests: Decode stval to identify
 exact exception type

On Tue, Apr 29, 2025 at 05:18:46PM -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
> 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),

We should never get csr accesses to the rv32 high registers since we only
support 64-bit.

> +		       "Unexpected csr_num 0x%x\n", csr_num);
> +
>  	illegal_handler_invoked = true;
>  	/* skip the trapping instruction */
>  	regs->epc += 4;
> 
> -- 
> 2.43.0
>

Otherwise,

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>