by Sean Christopherson

[permalink] [raw]

Subject: Re: [PATCH 4/7] KVM: selftests: Test consistency of CPUID with num of Fixed counters

On Thu, Mar 23, 2023, Like Xu wrote:
> From: Jinrong Liang <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Like Xu <[email protected]>
> Signed-off-by: Jinrong Liang <[email protected]>
> ---
> .../selftests/kvm/x86_64/pmu_cpuid_test.c | 68 +++++++++++++++++++
> 1 file changed, 68 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c b/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> index 50902187d2c9..c934144be287 100644
> --- a/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> @@ -74,6 +74,22 @@ static uint8_t kvm_gp_ctrs_num(void)
> return (kvm_entry->eax & GP_CTR_NUM_MASK) >> GP_CTR_NUM_OFS_BIT;
> }
>
> +static uint8_t kvm_fixed_ctrs_num(void)
> +{
> + const struct kvm_cpuid_entry2 *kvm_entry;
> +
> + kvm_entry = get_cpuid_entry(kvm_get_supported_cpuid(), 0xa, 0);
> + return kvm_entry->edx & FIXED_CTR_NUM_MASK;
> +}
> +
> +static uint32_t kvm_fixed_ctrs_bitmask(void)
> +{
> + const struct kvm_cpuid_entry2 *kvm_entry;
> +
> + kvm_entry = get_cpuid_entry(kvm_get_supported_cpuid(), 0xa, 0);
> + return kvm_entry->ecx;
> +}

KVM_X86_CPU_PROPERTY

> static struct kvm_vcpu *new_vcpu(void *guest_code)
> {
> struct kvm_vm *vm;
> @@ -230,6 +246,39 @@ static void test_oob_gp_counter_setup(struct kvm_vcpu *vcpu, uint8_t eax_gp_num,
> vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
> }
>
> +static uint64_t test_oob_fixed_counter_setup(struct kvm_vcpu *vcpu,
> + uint8_t edx_fix_num,
> + uint32_t fixed_bitmask)
> +{
> + struct kvm_cpuid_entry2 *entry;
> + uint32_t ctr_msr = MSR_CORE_PERF_FIXED_CTR0;
> + uint8_t idx = edx_fix_num;
> + bool is_supported = true;

No need to initialize "true", it's explicitly set below.

> + uint64_t ret = 0xffffULL;
> +
> + 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, FixCtr[i]_is_supported := ECX[i] || (EDX[4:0] > i). */
> + is_supported = (entry->ecx & BIT_ULL(idx) ||
> + ((entry->edx & FIXED_CTR_NUM_MASK) > idx));
> +
> + /* KVM doesn't emulate more fixed counters than it can support. */
> + if (idx >= kvm_fixed_ctrs_num())
> + is_supported = false;

Why not this?

is_supported = idx < kvm_fixed_ctrs_num() &&
<CPUID entry stuff>;
> +
> + if (!is_supported) {
> + vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
> + ret = GP_VECTOR;
> + }

Same comments as the previous patch(es).

2023-05-25 00:07:19

by Jim Mattson

[permalink] [raw]

Subject: Re: [PATCH 4/7] KVM: selftests: Test consistency of CPUID with num of Fixed counters

On Thu, Mar 23, 2023 at 12:28 AM Like Xu <[email protected]> wrote:
>
> From: Jinrong Liang <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Like Xu <[email protected]>
> Signed-off-by: Jinrong Liang <[email protected]>
> ---
> .../selftests/kvm/x86_64/pmu_cpuid_test.c | 68 +++++++++++++++++++
> 1 file changed, 68 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c b/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> index 50902187d2c9..c934144be287 100644
> --- a/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/pmu_cpuid_test.c
> @@ -74,6 +74,22 @@ static uint8_t kvm_gp_ctrs_num(void)
> return (kvm_entry->eax & GP_CTR_NUM_MASK) >> GP_CTR_NUM_OFS_BIT;
> }
>
> +static uint8_t kvm_fixed_ctrs_num(void)
> +{
> + const struct kvm_cpuid_entry2 *kvm_entry;
> +
> + kvm_entry = get_cpuid_entry(kvm_get_supported_cpuid(), 0xa, 0);
> + return kvm_entry->edx & FIXED_CTR_NUM_MASK;
> +}
> +
> +static uint32_t kvm_fixed_ctrs_bitmask(void)
> +{
> + const struct kvm_cpuid_entry2 *kvm_entry;
> +
> + kvm_entry = get_cpuid_entry(kvm_get_supported_cpuid(), 0xa, 0);
> + return kvm_entry->ecx;
> +}
> +
> static struct kvm_vcpu *new_vcpu(void *guest_code)
> {
> struct kvm_vm *vm;
> @@ -230,6 +246,39 @@ static void test_oob_gp_counter_setup(struct kvm_vcpu *vcpu, uint8_t eax_gp_num,
> vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
> }
>
> +static uint64_t test_oob_fixed_counter_setup(struct kvm_vcpu *vcpu,
> + uint8_t edx_fix_num,
> + uint32_t fixed_bitmask)
> +{
> + struct kvm_cpuid_entry2 *entry;
> + uint32_t ctr_msr = MSR_CORE_PERF_FIXED_CTR0;
> + uint8_t idx = edx_fix_num;
> + bool is_supported = true;
> + uint64_t ret = 0xffffULL;
> +
> + 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, FixCtr[i]_is_supported := ECX[i] || (EDX[4:0] > i). */
> + is_supported = (entry->ecx & BIT_ULL(idx) ||
> + ((entry->edx & FIXED_CTR_NUM_MASK) > idx));
> +
> + /* KVM doesn't emulate more fixed counters than it can support. */
> + if (idx >= kvm_fixed_ctrs_num())
> + is_supported = false;
> +
> + if (!is_supported) {
> + vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
> + ret = GP_VECTOR;
> + }
> +
> + vcpu_args_set(vcpu, 4, ctr_msr, ret, idx, 1);
> +
> + return ret;
> +}
> +
> static void intel_check_arch_event_is_unavl(uint8_t idx)
> {
> const char *msg = "Unavailable arch event is counting.";

This test seems bogus to me. The event may not be available because it
is inaccurate. That doesn't imply that the count will always be zero.

> @@ -267,10 +316,23 @@ static void test_oob_gp_counter(uint8_t eax_gp_num, uint64_t perf_cap)
> free_vcpu(vcpu);
> }
>
> +static void intel_test_oob_fixed_ctr(uint8_t edx_fix_num, uint32_t fixed_bitmask)
> +{
> + const char *msg = "At least one unsupported Fixed counter is visible.";

This test seems bogus to me. Unsupported does not imply invisible.

> + struct kvm_vcpu *vcpu;
> + uint64_t ret;
> +
> + vcpu = new_vcpu(guest_wr_and_rd_msrs);
> + ret = test_oob_fixed_counter_setup(vcpu, edx_fix_num, fixed_bitmask);
> + run_vcpu(vcpu, msg, first_uc_arg_equals, (void *)ret);
> + free_vcpu(vcpu);
> +}
> +
> static void intel_test_counters_num(void)
> {
> uint8_t kvm_gp_num = kvm_gp_ctrs_num();
> unsigned int i;
> + uint32_t ecx;
>
> TEST_REQUIRE(kvm_gp_num > 2);
>
> @@ -289,6 +351,12 @@ static void intel_test_counters_num(void)
> /* KVM doesn't emulate more counters than it can support. */
> test_oob_gp_counter(kvm_gp_num + 1, perf_caps[i]);
> }
> +
> + for (ecx = 0; ecx <= kvm_fixed_ctrs_bitmask() + 1; ecx++) {
> + intel_test_oob_fixed_ctr(0, ecx);
> + intel_test_oob_fixed_ctr(kvm_fixed_ctrs_num(), ecx);
> + intel_test_oob_fixed_ctr(kvm_fixed_ctrs_num() + 1, ecx);
> + }
> }
>
> static void intel_test_arch_events(void)
> --
> 2.40.0
>