Re: [PATCH 1/1] KVM: selftests: add kvmclock drift test

[Dongli Zhang]

Ping :)

BTW, I see Vitaly Kuznetsov has a patch to generalize check_clocksource(),
which is also used by this patch.

[PATCH 1/5] KVM: selftests: Generalize check_clocksource() from kvm_clock_test
https://lore.kernel.org/all/20240109141121.1619463-2-vkuznets@xxxxxxxxxx/

Thank you very much!

Dongli Zhang

On 1/6/24 00:33, Dongli Zhang wrote:
> There is kvmclock drift issue during the vCPU hotplug. It has been fixed by
> the commit c52ffadc65e2 ("KVM: x86: Don't unnecessarily force masterclock
> update on vCPU hotplug").
> 
> This is to add the test to verify if the master clock is updated when we
> write 0 to MSR_IA32_TSC from the host side.
> 
> Here is the usage example on the KVM with the bugfix reverted.
> 
> $ ./kvm_clock_drift -v -p 5
> kvmclock based on old pvclock_vcpu_time_info: 5012221999
>   version:           2
>   tsc_timestamp:     3277968
>   system_time:       11849519
>   tsc_to_system_mul: 2152530255
>   tsc_shift:         0
>   flags:             1
> 
> kvmclock based on new pvclock_vcpu_time_info: 5012222411
>   version:           4
>   tsc_timestamp:     9980576184
>   system_time:       5012222411
>   tsc_to_system_mul: 2152530255
>   tsc_shift:         0
>   flags:             1
> 
> ==== Test Assertion Failure ====
>   x86_64/kvm_clock_drift.c:216: clock_old == clock_new
>   pid=14257 tid=14257 errno=4 - Interrupted system call
>      1	0x000000000040277b: main at kvm_clock_drift.c:216
>      2	0x00007f7766fa7e44: ?? ??:0
>      3	0x000000000040286d: _start at ??:?
>   kvmclock drift detected, old=5012221999, new=5012222411
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/Makefile          |   1 +
>  .../selftests/kvm/x86_64/kvm_clock_drift.c    | 223 ++++++++++++++++++
>  2 files changed, 224 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 4412b42d95de..c665d0d8d348 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -84,6 +84,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/hyperv_features
>  TEST_GEN_PROGS_x86_64 += x86_64/hyperv_ipi
>  TEST_GEN_PROGS_x86_64 += x86_64/hyperv_svm_test
>  TEST_GEN_PROGS_x86_64 += x86_64/hyperv_tlb_flush
> +TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_drift
>  TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_test
>  TEST_GEN_PROGS_x86_64 += x86_64/kvm_pv_test
>  TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
> diff --git a/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c b/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c
> new file mode 100644
> index 000000000000..324f0dbc5762
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c
> @@ -0,0 +1,223 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * The kvmclock drift test. Emulate vCPU hotplug and online to verify if
> + * there is kvmclock drift.
> + *
> + * Adapted from steal_time.c
> + *
> + * Copyright (C) 2020, Red Hat, Inc.
> + * Copyright (C) 2024 Oracle and/or its affiliates.
> + */
> +
> +#include <asm/kvm_para.h>
> +#include <asm/pvclock.h>
> +#include <asm/pvclock-abi.h>
> +#include <sys/stat.h>
> +
> +#include "kvm_util.h"
> +#include "processor.h"
> +
> +#define NR_VCPUS		2
> +#define NR_SLOTS		2
> +#define KVMCLOCK_SIZE		sizeof(struct pvclock_vcpu_time_info)
> +/*
> + * KVMCLOCK_GPA is identity mapped
> + */
> +#define KVMCLOCK_GPA		(1 << 30)
> +
> +static uint64_t kvmclock_gpa = KVMCLOCK_GPA;
> +
> +static void guest_code(int cpu)
> +{
> +	struct pvclock_vcpu_time_info *kvmclock;
> +
> +	/*
> +	 * vCPU#0 is to detect the change of pvclock_vcpu_time_info
> +	 */
> +	if (cpu == 0) {
> +		GUEST_SYNC(0);
> +
> +		kvmclock = (struct pvclock_vcpu_time_info *) kvmclock_gpa;
> +		wrmsr(MSR_KVM_SYSTEM_TIME_NEW, kvmclock_gpa | KVM_MSR_ENABLED);
> +
> +		/*
> +		 * Backup the pvclock_vcpu_time_info before vCPU#1 hotplug
> +		 */
> +		kvmclock[1] = kvmclock[0];
> +
> +		GUEST_SYNC(2);
> +		/*
> +		 * Enter the guest to update pvclock_vcpu_time_info
> +		 */
> +		GUEST_SYNC(4);
> +	}
> +
> +	/*
> +	 * vCPU#1 is to emulate the vCPU hotplug
> +	 */
> +	if (cpu == 1) {
> +		GUEST_SYNC(1);
> +		/*
> +		 * This is after the host side MSR_IA32_TSC
> +		 */
> +		GUEST_SYNC(3);
> +	}
> +}
> +
> +static void run_vcpu(struct kvm_vcpu *vcpu)
> +{
> +	struct ucall uc;
> +
> +	vcpu_run(vcpu);
> +
> +	switch (get_ucall(vcpu, &uc)) {
> +	case UCALL_SYNC:
> +	case UCALL_DONE:
> +		break;
> +	case UCALL_ABORT:
> +		REPORT_GUEST_ASSERT(uc);
> +	default:
> +		TEST_ASSERT(false, "Unexpected exit: %s",
> +			    exit_reason_str(vcpu->run->exit_reason));
> +	}
> +}
> +
> +static void kvmclock_dump(struct pvclock_vcpu_time_info *kvmclock)
> +{
> +	pr_info("  version:           %u\n", kvmclock->version);
> +	pr_info("  tsc_timestamp:     %lu\n", kvmclock->tsc_timestamp);
> +	pr_info("  system_time:       %lu\n", kvmclock->system_time);
> +	pr_info("  tsc_to_system_mul: %u\n", kvmclock->tsc_to_system_mul);
> +	pr_info("  tsc_shift:         %d\n", kvmclock->tsc_shift);
> +	pr_info("  flags:             %u\n", kvmclock->flags);
> +	pr_info("\n");
> +}
> +
> +#define CLOCKSOURCE_PATH "/sys/devices/system/clocksource/clocksource0/current_clocksource"
> +
> +static void check_clocksource(void)
> +{
> +	char *clk_name;
> +	struct stat st;
> +	FILE *fp;
> +
> +	fp = fopen(CLOCKSOURCE_PATH, "r");
> +	if (!fp) {
> +		pr_info("failed to open clocksource file: %d; assuming TSC.\n",
> +			errno);
> +		return;
> +	}
> +
> +	if (fstat(fileno(fp), &st)) {
> +		pr_info("failed to stat clocksource file: %d; assuming TSC.\n",
> +			errno);
> +		goto out;
> +	}
> +
> +	clk_name = malloc(st.st_size);
> +	TEST_ASSERT(clk_name, "failed to allocate buffer to read file\n");
> +
> +	if (!fgets(clk_name, st.st_size, fp)) {
> +		pr_info("failed to read clocksource file: %d; assuming TSC.\n",
> +			ferror(fp));
> +		goto out;
> +	}
> +
> +	TEST_ASSERT(!strncmp(clk_name, "tsc\n", st.st_size),
> +		    "clocksource not supported: %s", clk_name);
> +out:
> +	fclose(fp);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct pvclock_vcpu_time_info *kvmclock;
> +	struct kvm_vcpu *vcpus[NR_VCPUS];
> +	uint64_t clock_old, clock_new;
> +	bool verbose = false;
> +	unsigned int gpages;
> +	struct kvm_vm *vm;
> +	int period = 2;
> +	uint64_t tsc;
> +	int opt;
> +
> +	check_clocksource();
> +
> +	while ((opt = getopt(argc, argv, "p:vh")) != -1) {
> +		switch (opt) {
> +		case 'p':
> +			period = atoi_positive("The period (seconds) between vCPU hotplug",
> +					       optarg);
> +			break;
> +		case 'v':
> +			verbose = true;
> +			break;
> +		case 'h':
> +		default:
> +			pr_info("usage: %s [-p period (seconds)] [-v]\n", argv[0]);
> +			exit(1);
> +		}
> +	}
> +
> +	vm = vm_create_with_vcpus(NR_VCPUS, guest_code, vcpus);
> +	gpages = vm_calc_num_guest_pages(VM_MODE_DEFAULT,
> +					 KVMCLOCK_SIZE * NR_SLOTS);
> +	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
> +				    KVMCLOCK_GPA, 1, gpages, 0);
> +	virt_map(vm, KVMCLOCK_GPA, KVMCLOCK_GPA, gpages);
> +
> +	vcpu_args_set(vcpus[0], 1, 0);
> +	vcpu_args_set(vcpus[1], 1, 1);
> +
> +	/*
> +	 * Run vCPU#0 and vCPU#1 to update both pvclock_vcpu_time_info and
> +	 * master clock
> +	 */
> +	run_vcpu(vcpus[0]);
> +	run_vcpu(vcpus[1]);
> +
> +	/*
> +	 * Run vCPU#0 to backup the current pvclock_vcpu_time_info
> +	 */
> +	run_vcpu(vcpus[0]);
> +
> +	sleep(period);
> +
> +	/*
> +	 * Emulate the hotplug of vCPU#1
> +	 */
> +	vcpu_set_msr(vcpus[1], MSR_IA32_TSC, 0);
> +
> +	/*
> +	 * Emulate the online of vCPU#1
> +	 */
> +	run_vcpu(vcpus[1]);
> +
> +	/*
> +	 * Run vCPU#0 to backup the new pvclock_vcpu_time_info to detect
> +	 * if there is any change or kvmclock drift
> +	 */
> +	run_vcpu(vcpus[0]);
> +
> +	kvmclock = addr_gva2hva(vm, kvmclock_gpa);
> +	tsc = kvmclock[0].tsc_timestamp;
> +	clock_old = __pvclock_read_cycles(&kvmclock[1], tsc);
> +	clock_new = __pvclock_read_cycles(&kvmclock[0], tsc);
> +
> +	if (verbose) {
> +		pr_info("kvmclock based on old pvclock_vcpu_time_info: %lu\n",
> +			clock_old);
> +		kvmclock_dump(&kvmclock[1]);
> +		pr_info("kvmclock based on new pvclock_vcpu_time_info: %lu\n",
> +			clock_new);
> +		kvmclock_dump(&kvmclock[0]);
> +	}
> +
> +	TEST_ASSERT(clock_old == clock_new,
> +		    "kvmclock drift detected, old=%lu, new=%lu",
> +		    clock_old, clock_new);
> +
> +	kvm_vm_free(vm);
> +
> +	return 0;
> +}
> 
> base-commit: f2a3fb7234e52f72ff4a38364dbf639cf4c7d6c6