Re: [PATCH v4 3/3] KVM: selftests: Test behavior of KVM_X86_DISABLE_EXITS_APERFMPERF

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 5/31/2025 2:52 AM, Jim Mattson wrote:
> For a VCPU thread pinned to a single LPU, verify that interleaved host
> and guest reads of IA32_[AM]PERF return strictly increasing values when
> APERFMPERF exiting is disabled.
>
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---
>  tools/testing/selftests/kvm/Makefile.kvm      |   1 +
>  .../testing/selftests/kvm/include/kvm_util.h  |   2 +
>  tools/testing/selftests/kvm/lib/kvm_util.c    |  17 +++
>  .../selftests/kvm/x86/aperfmperf_test.c       | 132 ++++++++++++++++++
>  4 files changed, 152 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/x86/aperfmperf_test.c
>
> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index 3e786080473d..8d42a3bd0dd8 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -131,6 +131,7 @@ TEST_GEN_PROGS_x86 += x86/amx_test
>  TEST_GEN_PROGS_x86 += x86/max_vcpuid_cap_test
>  TEST_GEN_PROGS_x86 += x86/triple_fault_event_test
>  TEST_GEN_PROGS_x86 += x86/recalc_apic_map_test
> +TEST_GEN_PROGS_x86 += x86/aperfmperf_test
>  TEST_GEN_PROGS_x86 += access_tracking_perf_test
>  TEST_GEN_PROGS_x86 += coalesced_io_test
>  TEST_GEN_PROGS_x86 += dirty_log_perf_test
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 93013564428b..43a1bef10ec0 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -1158,4 +1158,6 @@ bool vm_is_gpa_protected(struct kvm_vm *vm, vm_paddr_t paddr);
>  
>  uint32_t guest_get_vcpuid(void);
>  
> +int pin_task_to_one_cpu(void);
> +
>  #endif /* SELFTEST_KVM_UTIL_H */
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index 5649cf2f40e8..b6c707ab92d7 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> @@ -10,6 +10,7 @@
>  #include "ucall_common.h"
>  
>  #include <assert.h>
> +#include <pthread.h>
>  #include <sched.h>
>  #include <sys/mman.h>
>  #include <sys/resource.h>
> @@ -2321,3 +2322,19 @@ bool vm_is_gpa_protected(struct kvm_vm *vm, vm_paddr_t paddr)
>  	pg = paddr >> vm->page_shift;
>  	return sparsebit_is_set(region->protected_phy_pages, pg);
>  }
> +
> +int pin_task_to_one_cpu(void)
> +{
> +	int cpu = sched_getcpu();
> +	cpu_set_t cpuset;
> +	int rc;
> +
> +	CPU_ZERO(&cpuset);
> +	CPU_SET(cpu, &cpuset);
> +
> +	rc = pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
> +	TEST_ASSERT(rc == 0, "%s: Can't set thread affinity", __func__);
> +
> +	return cpu;
> +}
> +
> diff --git a/tools/testing/selftests/kvm/x86/aperfmperf_test.c b/tools/testing/selftests/kvm/x86/aperfmperf_test.c
> new file mode 100644
> index 000000000000..64d976156693
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86/aperfmperf_test.c
> @@ -0,0 +1,132 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Test for KVM_X86_DISABLE_EXITS_APERFMPERF
> + *
> + * Copyright (C) 2025, Google LLC.
> + *
> + * Test the ability to disable VM-exits for rdmsr of IA32_APERF and
> + * IA32_MPERF. When these VM-exits are disabled, reads of these MSRs
> + * return the host's values.
> + *
> + * Note: Requires read access to /dev/cpu/<lpu>/msr to read host MSRs.
> + */
> +
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <unistd.h>
> +#include <asm/msr-index.h>
> +
> +#include "kvm_util.h"
> +#include "processor.h"
> +#include "test_util.h"
> +
> +#define NUM_ITERATIONS 100
> +
> +static int open_dev_msr(int cpu)
> +{
> +	char path[PATH_MAX];
> +
> +	snprintf(path, sizeof(path), "/dev/cpu/%d/msr", cpu);
> +	return open_path_or_exit(path, O_RDONLY);
> +}
> +
> +static uint64_t read_dev_msr(int msr_fd, uint32_t msr)
> +{
> +	uint64_t data;
> +	ssize_t rc;
> +
> +	rc = pread(msr_fd, &data, sizeof(data), msr);
> +	TEST_ASSERT(rc == sizeof(data), "Read of MSR 0x%x failed", msr);
> +
> +	return data;
> +}
> +
> +static void guest_code(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < NUM_ITERATIONS; i++)
> +		GUEST_SYNC2(rdmsr(MSR_IA32_APERF), rdmsr(MSR_IA32_MPERF));
> +
> +	GUEST_DONE();
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	uint64_t host_aperf_before, host_mperf_before;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	int msr_fd;
> +	int cpu;
> +	int i;
> +
> +	cpu = pin_task_to_one_cpu();
> +
> +	msr_fd = open_dev_msr(cpu);
> +
> +	/*
> +	 * This test requires a non-standard VM initialization, because
> +	 * KVM_ENABLE_CAP cannot be used on a VM file descriptor after
> +	 * a VCPU has been created.
> +	 */
> +	vm = vm_create(1);
> +
> +	TEST_REQUIRE(vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS) &
> +		     KVM_X86_DISABLE_EXITS_APERFMPERF);
> +
> +	vm_enable_cap(vm, KVM_CAP_X86_DISABLE_EXITS,
> +		      KVM_X86_DISABLE_EXITS_APERFMPERF);
> +
> +	vcpu = vm_vcpu_add(vm, 0, guest_code);
> +
> +	host_aperf_before = read_dev_msr(msr_fd, MSR_IA32_APERF);
> +	host_mperf_before = read_dev_msr(msr_fd, MSR_IA32_MPERF);
> +
> +	for (i = 0; i < NUM_ITERATIONS; i++) {
> +		uint64_t host_aperf_after, host_mperf_after;
> +		uint64_t guest_aperf, guest_mperf;
> +		struct ucall uc;
> +
> +		vcpu_run(vcpu);
> +		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_DONE:
> +			break;
> +		case UCALL_ABORT:
> +			REPORT_GUEST_ASSERT(uc);
> +		case UCALL_SYNC:
> +			guest_aperf = uc.args[0];
> +			guest_mperf = uc.args[1];
> +
> +			host_aperf_after = read_dev_msr(msr_fd, MSR_IA32_APERF);
> +			host_mperf_after = read_dev_msr(msr_fd, MSR_IA32_MPERF);
> +
> +			TEST_ASSERT(host_aperf_before < guest_aperf,
> +				    "APERF: host_before (0x%" PRIx64 ") >= guest (0x%" PRIx64 ")",
> +				    host_aperf_before, guest_aperf);
> +			TEST_ASSERT(guest_aperf < host_aperf_after,
> +				    "APERF: guest (0x%" PRIx64 ") >= host_after (0x%" PRIx64 ")",
> +				    guest_aperf, host_aperf_after);
> +			TEST_ASSERT(host_mperf_before < guest_mperf,
> +				    "MPERF: host_before (0x%" PRIx64 ") >= guest (0x%" PRIx64 ")",
> +				    host_mperf_before, guest_mperf);
> +			TEST_ASSERT(guest_mperf < host_mperf_after,
> +				    "MPERF: guest (0x%" PRIx64 ") >= host_after (0x%" PRIx64 ")",
> +				    guest_mperf, host_mperf_after);

Should we consider the possible overflow case of these 2 MSRs although it
could be extremely rare? Thanks.


> +
> +			host_aperf_before = host_aperf_after;
> +			host_mperf_before = host_mperf_after;
> +
> +			break;
> +		}
> +	}
> +
> +	kvm_vm_free(vm);
> +	close(msr_fd);
> +
> +	return 0;
> +}