linux-kernel - Re: [PATCH v5 20/22] KVM: riscv: selftests: Add SBI PMU selftest

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Message-ID: <20240409-dd055c3d08e027cf2a5cb4dc@orel>
Date: Tue, 9 Apr 2024 10:01:48 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Atish Patra <atishp@...osinc.com>
Cc: linux-kernel@...r.kernel.org, Anup Patel <anup@...infault.org>, 
	Ajay Kaher <akaher@...are.com>, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Alexey Makhalov <amakhalov@...are.com>, Conor Dooley <conor.dooley@...rochip.com>, 
	Juergen Gross <jgross@...e.com>, kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Shuah Khan <shuah@...nel.org>, virtualization@...ts.linux.dev, 
	VMware PV-Drivers Reviewers <pv-drivers@...are.com>, Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v5 20/22] KVM: riscv: selftests: Add SBI PMU selftest

On Mon, Apr 08, 2024 at 05:37:19PM -0700, Atish Patra wrote:
> On 4/5/24 05:50, Andrew Jones wrote:
> > On Wed, Apr 03, 2024 at 01:04:49AM -0700, Atish Patra wrote:
> > ...
> > > +static void test_pmu_basic_sanity(void)
> > > +{
> > > +	long out_val = 0;
> > > +	bool probe;
> > > +	struct sbiret ret;
> > > +	int num_counters = 0, i;
> > > +	union sbi_pmu_ctr_info ctrinfo;
> > > +
> > > +	probe = guest_sbi_probe_extension(SBI_EXT_PMU, &out_val);
> > > +	GUEST_ASSERT(probe && out_val == 1);
> > > +
> > > +	num_counters = get_num_counters();
> > > +
> > > +	for (i = 0; i < num_counters; i++) {
> > > +		ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_GET_INFO, i,
> > > +				0, 0, 0, 0, 0);
> > > +
> > > +		/* There can be gaps in logical counter indicies*/
> > > +		if (ret.error)
> > > +			continue;
> > > +		GUEST_ASSERT_NE(ret.value, 0);
> > > +
> > > +		ctrinfo.value = ret.value;
> > > +
> > > +		/**
> > > +		 * Accesibillity check of hardware and read capability of firmware counters.
> > 
> > Accessibility
> > 
> 
> Fixed it.
> 
> > > +		 * The spec doesn't mandate any initial value. No need to check any value.
> > > +		 */
> > > +		read_counter(i, ctrinfo);
> > > +	}
> > > +
> > > +	GUEST_DONE();
> > > +}
> > > +
> > > +static void run_vcpu(struct kvm_vcpu *vcpu)
> > > +{
> > > +	struct ucall uc;
> > > +
> > > +	vcpu_run(vcpu);
> > > +	switch (get_ucall(vcpu, &uc)) {
> > > +	case UCALL_ABORT:
> > > +		REPORT_GUEST_ASSERT(uc);
> > > +		break;
> > > +	case UCALL_DONE:
> > > +	case UCALL_SYNC:
> > > +		break;
> > > +	default:
> > > +		TEST_FAIL("Unknown ucall %lu", uc.cmd);
> > > +		break;
> > > +	}
> > > +}
> > > +
> > > +void test_vm_destroy(struct kvm_vm *vm)
> > > +{
> > > +	memset(ctrinfo_arr, 0, sizeof(union sbi_pmu_ctr_info) * RISCV_MAX_PMU_COUNTERS);
> > > +	counter_mask_available = 0;
> > > +	kvm_vm_free(vm);
> > > +}
> > > +
> > > +static void test_vm_basic_test(void *guest_code)
> > > +{
> > > +	struct kvm_vm *vm;
> > > +	struct kvm_vcpu *vcpu;
> > > +
> > > +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> > > +	__TEST_REQUIRE(__vcpu_has_sbi_ext(vcpu, KVM_RISCV_SBI_EXT_PMU),
> > > +				   "SBI PMU not available, skipping test");
> > > +	vm_init_vector_tables(vm);
> > > +	/* Illegal instruction handler is required to verify read access without configuration */
> > > +	vm_install_exception_handler(vm, EXC_INST_ILLEGAL, guest_illegal_exception_handler);
> > 
> > I still don't see where the "verify" part is. The handler doesn't record
> > that it had to handle anything.
> > 
> 
> The objective of the test is to ensure that we get an illegal instruction
> without configuration.

This part I guessed.

> The presence of the registered exception handler is
> sufficient for that.

This part I disagree with. The handler may not be necessary and not run if
we don't get the ILL. Usually when I write tests like these I set a
boolean in the handler and check it after the instruction which should
have sent us there to make sure we did indeed go there.

> 
> The verify part is that the test doesn't end up in a illegal instruction
> exception when you try to access a counter without configuring.
> 
> Let me know if you think we should more verbose comment to explain the
> scenario.
> 

With a boolean the test code will be mostly self documenting, but a short
comment saying why we expect the boolean to be set would be good too.

Thanks,
drew

> 
> > > +
> > > +	vcpu_init_vector_tables(vcpu);
> > > +	run_vcpu(vcpu);
> > > +
> > > +	test_vm_destroy(vm);
> > > +}
> > > +
> > > +static void test_vm_events_test(void *guest_code)
> > > +{
> > > +	struct kvm_vm *vm = NULL;
> > > +	struct kvm_vcpu *vcpu = NULL;
> > > +
> > > +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> > > +	__TEST_REQUIRE(__vcpu_has_sbi_ext(vcpu, KVM_RISCV_SBI_EXT_PMU),
> > > +				   "SBI PMU not available, skipping test");
> > > +	run_vcpu(vcpu);
> > > +
> > > +	test_vm_destroy(vm);
> > > +}
> > > +
> > > +int main(void)
> > > +{
> > > +	test_vm_basic_test(test_pmu_basic_sanity);
> > > +	pr_info("SBI PMU basic test : PASS\n");
> > > +
> > > +	test_vm_events_test(test_pmu_events);
> > > +	pr_info("SBI PMU event verification test : PASS\n");
> > > +
> > > +	return 0;
> > > +}
> > > -- 
> > > 2.34.1
> > > 
> > 
> > Thanks,
> > drew
>