| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <aBAqzZOiCCYWgOrM@google.com>
Date: Mon, 28 Apr 2025 18:26:37 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jim Mattson <jmattson@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 2/2] KVM: selftests: Test behavior of KVM_X86_DISABLE_EXITS_APERFMPERF
On Fri, Mar 21, 2025, Jim Mattson wrote:
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <pthread.h>
> +#include <sched.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 void pin_thread(int cpu)
> +{
> + 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__);
Heh, you copy-pasted this from hardware_disable_test.c, didn't you? :-)
Would it make sense to turn this into a generic API that takes care of the entire
sched_getcpu() => pthread_setaffinity_np()? E.g. kvm_pin_task_to_current_cpu().
I suspect there are other (potential) tests that don't care about what CPU they
run on, so long as the test is pinned.
> +}
> +
> +static int open_dev_msr(int cpu)
> +{
> + char path[PATH_MAX];
> + int msr_fd;
> +
> + snprintf(path, sizeof(path), "/dev/cpu/%d/msr", cpu);
> + msr_fd = open(path, O_RDONLY);
> + __TEST_REQUIRE(msr_fd >= 0, "Can't open %s for read", path);
Please use open_path_or_exit().
Hmm, and I'm planning on posting a small series to add a variant that takes an
ENOENT message, and spits out a (hopefully) helpful message for the EACCES case.
It would be nice to have this one spit out something like "Is msk.ko loaded?",
but I would say don't worry about trying to coordinate anything. Worst case
scenario we can add a help message when the dust settles.
> + return msr_fd;
> +}
> +
> +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++) {
> + uint64_t aperf = rdmsr(MSR_IA32_APERF);
> + uint64_t mperf = rdmsr(MSR_IA32_MPERF);
> +
> + GUEST_SYNC2(aperf, mperf);
Does the test generate multiple RDMSR per MSR if you do:
GUEST_SYNC2(rdmsr(MSR_IA32_APERF), rdmsr(MSR_IA32_MPERF));
If the code generation comes out
> + }
> +
> + GUEST_DONE();
> +}
> +
> +static bool kvm_can_disable_aperfmperf_exits(struct kvm_vm *vm)
> +{
> + int flags = vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS);
> +
> + return flags & KVM_X86_DISABLE_EXITS_APERFMPERF;
> +}
Please don't add one-off helpers like this, especially when they're the condition
for TEST_REQUIRE(). I *want* the gory details if the test is skipped, so that I
don't have to go look at the source code to figure out what's missing.
And it's literally more code.
> +
> +int main(int argc, char *argv[])
> +{
> + uint64_t host_aperf_before, host_mperf_before;
> + int cpu = sched_getcpu();
> + struct kvm_vcpu *vcpu;
> + struct kvm_vm *vm;
> + int msr_fd;
> + int i;
> +
> + pin_thread(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.
Hrm, we should really sort this out. Every test that needs to enable a capability
is having to copy+paste this pattern. I don't love the idea of expanding
__vm_create_with_one_vcpu(), but there's gotta be a solution that isn't horrible,
and anything is better than endly copy paste.
> + */
> + vm = vm_create(1);
> +
> + TEST_REQUIRE(kvm_can_disable_aperfmperf_exits(vm));
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 (%lu) >= guest (%lu)",
> + host_aperf_before, guest_aperf);
Honest question, is decimal really better than hex for these?
> + TEST_ASSERT(guest_aperf < host_aperf_after,
> + "APERF: guest (%lu) >= host_after (%lu)",
> + guest_aperf, host_aperf_after);
> + TEST_ASSERT(host_mperf_before < guest_mperf,
> + "MPERF: host_before (%lu) >= guest (%lu)",
> + host_mperf_before, guest_mperf);
> + TEST_ASSERT(guest_mperf < host_mperf_after,
> + "MPERF: guest (%lu) >= host_after (%lu)",
> + guest_mperf, host_mperf_after);
> +
> + host_aperf_before = host_aperf_after;
> + host_mperf_before = host_mperf_after;
> +
> + break;
> + }
> + }
> +
> + TEST_ASSERT_EQ(i, NUM_ITERATIONS);
Why?
Powered by blists - more mailing lists