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Message-ID: <574f8adc-6aea-4460-9211-685091a30f5e@linux.intel.com>
Date: Tue, 10 Jun 2025 16:42:30 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 3/3] KVM: selftests: Test behavior of
KVM_X86_DISABLE_EXITS_APERFMPERF
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@...gle.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;
> +}
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