linux-kernel - Re: [PATCH v2 6/8] KVM: selftests: Test consistency of CPUID with num of fixed counters

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Date:   Wed, 28 Jun 2023 14:01:51 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jinrong Liang <ljr.kernel@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Like Xu <likexu@...cent.com>,
        David Matlack <dmatlack@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jinrong Liang <cloudliang@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/8] KVM: selftests: Test consistency of CPUID with num
 of fixed counters

On Tue, May 30, 2023, Jinrong Liang wrote:
> From: Jinrong Liang <cloudliang@...cent.com>
> 
> Add test to check if non-existent counters can be accessed in guest after
> determining the number of Intel generic performance counters by CPUID.
> Per SDM, fixed-function performance counter 'i' is supported if ECX[i] ||
> (EDX[4:0] > i). KVM doesn't emulate more counters than it can support.
> 
> Co-developed-by: Like Xu <likexu@...cent.com>
> Signed-off-by: Like Xu <likexu@...cent.com>
> Signed-off-by: Jinrong Liang <cloudliang@...cent.com>
> ---
>  .../kvm/x86_64/pmu_basic_functionality_test.c | 42 +++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> index 116437ac2095..e19f8c2774c5 100644
> --- a/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/pmu_basic_functionality_test.c
> @@ -228,10 +228,46 @@ static void test_oob_gp_counter(uint8_t eax_gp_num, uint8_t offset,
>  	kvm_vm_free(vm);
>  }
>  
> +static void intel_test_oob_fixed_ctr(uint8_t edx_fix_num,
> +				     uint32_t fixed_bitmask, uint64_t expected)
> +{
> +	struct kvm_vm *vm;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_cpuid_entry2 *entry;
> +	uint8_t idx = edx_fix_num;
> +	bool visible;
> +	uint64_t msr_val;
> +
> +	vm = pmu_vm_create_with_one_vcpu(&vcpu, guest_wr_and_rd_msrs);
> +
> +	entry = vcpu_get_cpuid_entry(vcpu, 0xa);
> +	entry->ecx = fixed_bitmask;
> +	entry->edx = (entry->edx & ~FIXED_CTR_NUM_MASK) | edx_fix_num;
> +	vcpu_set_cpuid(vcpu);
> +
> +	/* Per Intel SDM, FxCtr[i]_is_supported := ECX[i] || (EDX[4:0] > i). */
> +	visible = (entry->ecx & BIT_ULL(idx) ||
> +			((entry->edx & FIXED_CTR_NUM_MASK) > idx));

Add a helper (in pmu.h) for this one too.

> +	/* KVM doesn't emulate more fixed counters than it can support. */
> +	if (idx >= X86_INTEL_MAX_FIXED_CTR_NUM)
> +		visible = false;
> +
> +	vcpu_args_set(vcpu, 4, MSR_CORE_PERF_FIXED_CTR0, 0xffff, idx, 1);
> +	if (!visible)

Curly braces need around a multi-line statement.

> +		while (run_vcpu(vcpu, &msr_val) != UCALL_DONE)
> +			TEST_ASSERT(msr_val == expected,
> +				    "Unexpected when testing fixed counter num.");

ASSERT_EQ() will print the expected versus actually for you.