Re: [REPOST PATCH 09/16] selftests: KVM: aarch64: Add KVM PMU event filter test

Reiji Watanabe
2023-03-04T20:29:32Z

Hi Raghu,

On Tue, Feb 14, 2023 at 5:07 PM Raghavendra Rao Ananta
<rananta@google.com> wrote:
>
> Add tests to validate KVM's KVM_ARM_VCPU_PMU_V3_FILTER
> attribute by applying a series of filters to allow or
> deny events from the userspace. Validation is done by
> the guest in a way that it should be able to count
> only the events that are allowed.
>
> The workload to execute a precise number of instructions
> (execute_precise_instrs() and precise_instrs_loop()) is taken
> from the kvm-unit-tests' arm/pmu.c.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
> .../testing/selftests/kvm/aarch64/vpmu_test.c | 261 +++++++++++++++++-
> 1 file changed, 258 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/aarch64/vpmu_test.c b/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> index 2b3a4fa3afa9c..3dfb770b538e9 100644
> --- a/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> +++ b/tools/testing/selftests/kvm/aarch64/vpmu_test.c
> @@ -2,12 +2,21 @@
> /*
> * vpmu_test - Test the vPMU
> *
> - * Copyright (c) 2022 Google LLC.
> + * The test suit contains a series of checks to validate the vPMU
> + * functionality. This test runs only when KVM_CAP_ARM_PMU_V3 is
> + * supported on the host. The tests include:
> *
> - * This test checks if the guest can see the same number of the PMU event
> + * 1. Check if the guest can see the same number of the PMU event
> * counters (PMCR_EL0.N) that userspace sets, if the guest can access
> * those counters, and if the guest cannot access any other counters.
> - * This test runs only when KVM_CAP_ARM_PMU_V3 is supported on the host.
> + *
> + * 2. Test the functionality of KVM's KVM_ARM_VCPU_PMU_V3_FILTER
> + * attribute by applying a series of filters in various combinations
> + * of allowing or denying the events. The guest validates it by
> + * checking if it's able to count only the events that are allowed.
> + *
> + * Copyright (c) 2022 Google LLC.
> + *
> */
> #include <kvm_util.h>
> #include <processor.h>
> @@ -230,6 +239,12 @@ struct pmc_accessor pmc_accessors[] = {
>
> #define MAX_EVENT_FILTERS_PER_VM 10
>
> +#define EVENT_ALLOW(ev) \
> + {.base_event = ev, .nevents = 1, .action = KVM_PMU_EVENT_ALLOW}
> +
> +#define EVENT_DENY(ev) \
> + {.base_event = ev, .nevents = 1, .action = KVM_PMU_EVENT_DENY}
> +
> #define INVALID_EC (-1ul)
> uint64_t expected_ec = INVALID_EC;
> uint64_t op_end_addr;
> @@ -243,11 +258,13 @@ struct vpmu_vm {
>
> enum test_stage {
> TEST_STAGE_COUNTER_ACCESS = 1,
> + TEST_STAGE_KVM_EVENT_FILTER,
> };
>
> struct guest_data {
> enum test_stage test_stage;
> uint64_t expected_pmcr_n;
> + unsigned long *pmu_filter;
> };
>
> static struct guest_data guest_data;
> @@ -329,6 +346,113 @@ static bool pmu_event_is_supported(uint64_t event)
> GUEST_ASSERT_3(!(_tval & mask), _tval, mask, set_expected);\
> }
>
> +
> +/*
> + * Extra instructions inserted by the compiler would be difficult to compensate
> + * for, so hand assemble everything between, and including, the PMCR accesses
> + * to start and stop counting. isb instructions are inserted to make sure
> + * pmccntr read after this function returns the exact instructions executed
> + * in the controlled block. Total instrs = isb + nop + 2*loop = 2 + 2*loop.
> + */
> +static inline void precise_instrs_loop(int loop, uint32_t pmcr)
> +{
> + uint64_t pmcr64 = pmcr;
> +
> + asm volatile(
> + " msr pmcr_el0, %[pmcr]\n"
> + " isb\n"
> + "1: subs %w[loop], %w[loop], #1\n"
> + " b.gt 1b\n"
> + " nop\n"
> + " msr pmcr_el0, xzr\n"
> + " isb\n"
> + : [loop] "+r" (loop)
> + : [pmcr] "r" (pmcr64)
> + : "cc");
> +}
> +
> +/*
> + * Execute a known number of guest instructions. Only even instruction counts
> + * greater than or equal to 4 are supported by the in-line assembly code. The
> + * control register (PMCR_EL0) is initialized with the provided value (allowing
> + * for example for the cycle counter or event counters to be reset). At the end
> + * of the exact instruction loop, zero is written to PMCR_EL0 to disable
> + * counting, allowing the cycle counter or event counters to be read at the
> + * leisure of the calling code.
> + */
> +static void execute_precise_instrs(int num, uint32_t pmcr)
> +{
> + int loop = (num - 2) / 2;
> +
> + GUEST_ASSERT_2(num >= 4 && ((num - 2) % 2 == 0), num, loop);
> + precise_instrs_loop(loop, pmcr);
> +}
> +
> +static void test_instructions_count(int pmc_idx, bool expect_count)
> +{
> + int i;
> + struct pmc_accessor *acc;
> + uint64_t cnt;
> + int instrs_count = 100;
> +
> + enable_counter(pmc_idx);
> +
> + /* Test the event using all the possible way to configure the event */
> + for (i = 0; i < ARRAY_SIZE(pmc_accessors); i++) {
> + acc = &pmc_accessors[i];
> +
> + pmu_disable_reset();
> +
> + acc->write_typer(pmc_idx, ARMV8_PMUV3_PERFCTR_INST_RETIRED);
> +
> + /* Enable the PMU and execute precisely number of instructions as a workload */
> + execute_precise_instrs(instrs_count, read_sysreg(pmcr_el0) | ARMV8_PMU_PMCR_E);
> +
> + /* If a count is expected, the counter should be increased by 'instrs_count' */
> + cnt = acc->read_cntr(pmc_idx);
> + GUEST_ASSERT_4(expect_count == (cnt == instrs_count),
> + i, expect_count, cnt, instrs_count);
> + }
> +
> + disable_counter(pmc_idx);
> +}
> +
> +static void test_cycles_count(bool expect_count)
> +{
> + uint64_t cnt;
> +
> + pmu_enable();
> + reset_cycle_counter();
> +
> + /* Count cycles in EL0 and EL1 */
> + write_pmccfiltr(0);
> + enable_cycle_counter();
> +
> + cnt = read_cycle_counter();
> +
> + /*
> + * If a count is expected by the test, the cycle counter should be increased by
> + * at least 1, as there is at least one instruction between enabling the
> + * counter and reading the counter.
> + */
> + GUEST_ASSERT_2(expect_count == (cnt > 0), cnt, expect_count);
> +
> + disable_cycle_counter();

It would be nicer to also test using a generic PMC with
ARMV8_PMUV3_PERFCTR_CPU_CYCLES (not just with a cycle counter),
as the filter should be applied to both.

> + pmu_disable_reset();
> +}
> +
> +static void test_event_count(uint64_t event, int pmc_idx, bool expect_count)
> +{
> + switch (event) {
> + case ARMV8_PMUV3_PERFCTR_INST_RETIRED:
> + test_instructions_count(pmc_idx, expect_count);
> + break;
> + case ARMV8_PMUV3_PERFCTR_CPU_CYCLES:
> + test_cycles_count(expect_count);
> + break;
> + }
> +}
> +
> /*
> * Check if @mask bits in {PMCNTEN,PMINTEN,PMOVS}{SET,CLR} registers
> * are set or cleared as specified in @set_expected.
> @@ -532,12 +656,37 @@ static void guest_counter_access_test(uint64_t expected_pmcr_n)
> }
> }
>
> +static void guest_event_filter_test(unsigned long *pmu_filter)
> +{
> + uint64_t event;
> +
> + /*
> + * Check if PMCEIDx_EL0 is advertized as configured by the userspace.
> + * It's possible that even though the userspace allowed it, it may not be supported
> + * by the hardware and could be advertized as 'disabled'. Hence, only validate against
> + * the events that are advertized.

How about checking events that are supported by the hardware
initially (without setting the event filter) ?
Then, we can test if events that userspace tried to hide are
not exposed to guests correctly.

Can we also add a case for events that we can test both upper
32bits and lower 32 bits of both of PMCEID{0,1}_EL0 registers ?
(pmu_event_is_supported() needs to be fixed as well)

> + *
> + * Furthermore, check if the event is in fact counting if enabled, or vice-versa.
> + */
> + for (event = 0; event < ARMV8_PMU_MAX_EVENTS - 1; event++) {
> + if (pmu_event_is_supported(event)) {
> + GUEST_ASSERT_1(test_bit(event, pmu_filter), event);
> + test_event_count(event, 0, true);
> + } else {
> + test_event_count(event, 0, false);
> + }
> + }
> +}
> +
> static void guest_code(void)
> {
> switch (guest_data.test_stage) {
> case TEST_STAGE_COUNTER_ACCESS:
> guest_counter_access_test(guest_data.expected_pmcr_n);
> break;
> + case TEST_STAGE_KVM_EVENT_FILTER:
> + guest_event_filter_test(guest_data.pmu_filter);
> + break;
> default:
> GUEST_ASSERT_1(0, guest_data.test_stage);
> }

IMHO running a guest from a different guest_code_xxx might be more
straightforward rather than controlling through the test_stage,
as it appears each test 'stage' is a different test case rather than
a test stage, and the test creates a new guest for each test 'stage'.
I don't find any reason to share the guest_code for those test
cases (Unless we are going to run some common guest codes for test
cases in the following patches)

> @@ -760,9 +909,115 @@ static void run_counter_access_tests(uint64_t pmcr_n)
> run_counter_access_error_test(i);
> }
>
> +static struct kvm_pmu_event_filter pmu_event_filters[][MAX_EVENT_FILTERS_PER_VM] = {

It looks like KVM_ARM_VCPU_PMU_V3_FILTER is always used with
one entry in the filter (.nevents == 1).
Could we also test with .nevents > 1 ?

> + /*
> + * Each set of events denotes a filter configuration for that VM.
> + * During VM creation, the filters will be applied in the sequence mentioned here.
> + */
> + {
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + },
> + {
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + },
> + {
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + },
> + {
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + },
> + {
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + },
> + {
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + },
> + {
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_CPU_CYCLES),
> + },
> + {
> + EVENT_DENY(ARMV8_PMUV3_PERFCTR_INST_RETIRED),
> + },
> +};
> +
> +static void run_kvm_event_filter_error_tests(void)
> +{
> + int ret;
> + struct kvm_vm *vm;
> + struct kvm_vcpu *vcpu;
> + struct vpmu_vm *vpmu_vm;
> + struct kvm_vcpu_init init;
> + struct kvm_pmu_event_filter pmu_event_filter = EVENT_ALLOW(ARMV8_PMUV3_PERFCTR_CPU_CYCLES);
> + struct kvm_device_attr filter_attr = {
> + .group = KVM_ARM_VCPU_PMU_V3_CTRL,
> + .attr = KVM_ARM_VCPU_PMU_V3_FILTER,
> + .addr = (uint64_t) &pmu_event_filter,
> + };
> +
> + /* KVM should not allow configuring filters after the PMU is initialized */
> + vpmu_vm = create_vpmu_vm(guest_code, NULL);
> + ret = __vcpu_ioctl(vpmu_vm->vcpu, KVM_SET_DEVICE_ATTR, &filter_attr);
> + TEST_ASSERT(ret == -1 && errno == EBUSY,
> + "Failed to disallow setting an event filter after PMU init");
> + destroy_vpmu_vm(vpmu_vm);
> +
> + /* Check for invalid event filter setting */
> + vm = vm_create(1);
> + vm_ioctl(vm, KVM_ARM_PREFERRED_TARGET, &init);
> + init.features[0] |= (1 << KVM_ARM_VCPU_PMU_V3);
> + vcpu = aarch64_vcpu_add(vm, 0, &init, guest_code);
> +
> + pmu_event_filter.base_event = UINT16_MAX;
> + pmu_event_filter.nevents = 5;
> + ret = __vcpu_ioctl(vcpu, KVM_SET_DEVICE_ATTR, &filter_attr);
> + TEST_ASSERT(ret == -1 && errno == EINVAL, "Failed check for invalid filter configuration");
> + kvm_vm_free(vm);
> +}
> +
> +static void run_kvm_event_filter_test(void)
> +{
> + int i;
> + struct vpmu_vm *vpmu_vm;
> + struct kvm_vm *vm;
> + vm_vaddr_t pmu_filter_gva;
> + size_t pmu_filter_bmap_sz = BITS_TO_LONGS(ARMV8_PMU_MAX_EVENTS) * sizeof(unsigned long);
> +
> + guest_data.test_stage = TEST_STAGE_KVM_EVENT_FILTER;
> +
> + /* Test for valid filter configurations */
> + for (i = 0; i < ARRAY_SIZE(pmu_event_filters); i++) {
> + vpmu_vm = create_vpmu_vm(guest_code, pmu_event_filters[i]);
> + vm = vpmu_vm->vm;
> +
> + pmu_filter_gva = vm_vaddr_alloc(vm, pmu_filter_bmap_sz, KVM_UTIL_MIN_VADDR);
> + memcpy(addr_gva2hva(vm, pmu_filter_gva), vpmu_vm->pmu_filter, pmu_filter_bmap_sz);
> + guest_data.pmu_filter = (unsigned long *) pmu_filter_gva;
> +
> + run_vcpu(vpmu_vm->vcpu);
> +
> + destroy_vpmu_vm(vpmu_vm);
> + }
> +
> + /* Check if KVM is handling the errors correctly */
> + run_kvm_event_filter_error_tests();
> +}
> +
> static void run_tests(uint64_t pmcr_n)
> {
> run_counter_access_tests(pmcr_n);
> + run_kvm_event_filter_test();
> }
>
> /*
> --
> 2.39.1.581.gbfd45094c4-goog
>

Thank you,
Reiji