selftests: KVM: Introduce system counter offset test

  guest_tsc = host_tsc + KVM_VCPU_TSC_OFFSET

This attribute is useful for the precise migration of a guest's TSC. The

following describes a possible algorithm to use for the migration of a

guest's TSC:

This attribute is useful to adjust the guest's TSC on live migration,

so that the TSC counts the time during which the VM was paused. The

following describes a possible algorithm to use for this purpose.

From the source VMM process:

1. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (t_0),

   kvmclock nanoseconds (k_0), and realtime nanoseconds (r_0).

1. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (tsc_src),

   kvmclock nanoseconds (guest_src), and host CLOCK_REALTIME nanoseconds

   (host_src).

2. Read the KVM_VCPU_TSC_OFFSET attribute for every vCPU to record the

   guest TSC offset (off_n).

   guest TSC offset (ofs_src[i]).

3. Invoke the KVM_GET_TSC_KHZ ioctl to record the frequency of the

   guest's TSC (freq).

From the destination VMM process:

4. Invoke the KVM_SET_CLOCK ioctl, providing the kvmclock nanoseconds

   (k_0) and realtime nanoseconds (r_0) in their respective fields.

   Ensure that the KVM_CLOCK_REALTIME flag is set in the provided

   structure. KVM will advance the VM's kvmclock to account for elapsed

   time since recording the clock values.

4. Invoke the KVM_SET_CLOCK ioctl, providing the source nanoseconds from

   kvmclock (guest_src) and CLOCK_REALTIME (host_src) in their respective

   fields.  Ensure that the KVM_CLOCK_REALTIME flag is set in the provided

   structure.

5. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (t_1) and

   kvmclock nanoseconds (k_1).

   KVM will advance the VM's kvmclock to account for elapsed time since

   recording the clock values.  Note that this will cause problems in

   the guest (e.g., timeouts) unless CLOCK_REALTIME is synchronized

   between the source and destination, and a reasonably short time passes

   between the source pausing the VMs and the destination executing

   steps 4-7.

5. Invoke the KVM_GET_CLOCK ioctl to record the host TSC (tsc_dest) and

   kvmclock nanoseconds (guest_dest).

6. Adjust the guest TSC offsets for every vCPU to account for (1) time

   elapsed since recording state and (2) difference in TSCs between the

   source and destination machine:

   new_off_n = t_0 + off_n + (k_1 - k_0) * freq - t_1

   ofs_dst[i] = ofs_src[i] -

     (guest_src - guest_dest) * freq +

     (tsc_src - tsc_dest)

   ("ofs[i] + tsc - guest * freq" is the guest TSC value corresponding to

   a time of 0 in kvmclock.  The above formula ensures that it is the

   same on the destination as it was on the source).

7. Write the KVM_VCPU_TSC_OFFSET attribute for every vCPU with the

   respective value derived in the previous step.

/set_memory_region_test

/steal_time

/kvm_binary_stats_test

/system_counter_offset_test

TEST_GEN_PROGS_x86_64 += set_memory_region_test

TEST_GEN_PROGS_x86_64 += steal_time

TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test

TEST_GEN_PROGS_x86_64 += system_counter_offset_test

TEST_GEN_PROGS_aarch64 += aarch64/debug-exceptions

TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list

// SPDX-License-Identifier: GPL-2.0-only

/*

 * Copyright (C) 2021, Google LLC.

 *

 * Tests for adjusting the system counter from userspace

 */

#include <asm/kvm_para.h>

#include <stdint.h>

#include <string.h>

#include <sys/stat.h>

#include <time.h>

#include "test_util.h"

#include "kvm_util.h"

#include "processor.h"

#define VCPU_ID 0

#ifdef __x86_64__

struct test_case {

	uint64_t tsc_offset;

};

static struct test_case test_cases[] = {

	{ 0 },

	{ 180 * NSEC_PER_SEC },

	{ -180 * NSEC_PER_SEC },

};

static void check_preconditions(struct kvm_vm *vm)

{

	if (!_vcpu_has_device_attr(vm, VCPU_ID, KVM_VCPU_TSC_CTRL, KVM_VCPU_TSC_OFFSET))

		return;

	print_skip("KVM_VCPU_TSC_OFFSET not supported; skipping test");

	exit(KSFT_SKIP);

}

static void setup_system_counter(struct kvm_vm *vm, struct test_case *test)

{

	vcpu_access_device_attr(vm, VCPU_ID, KVM_VCPU_TSC_CTRL,

				KVM_VCPU_TSC_OFFSET, &test->tsc_offset, true);

}

static uint64_t guest_read_system_counter(struct test_case *test)

{

	return rdtsc();

}

static uint64_t host_read_guest_system_counter(struct test_case *test)

{

	return rdtsc() + test->tsc_offset;

}

#else /* __x86_64__ */

#error test not implemented for this architecture!

#endif

#define GUEST_SYNC_CLOCK(__stage, __val)			\

		GUEST_SYNC_ARGS(__stage, __val, 0, 0, 0)

static void guest_main(void)

{

	int i;

	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {

		struct test_case *test = &test_cases[i];

		GUEST_SYNC_CLOCK(i, guest_read_system_counter(test));

	}

}

static void handle_sync(struct ucall *uc, uint64_t start, uint64_t end)

{

	uint64_t obs = uc->args[2];

	TEST_ASSERT(start <= obs && obs <= end,

		    "unexpected system counter value: %"PRIu64" expected range: [%"PRIu64", %"PRIu64"]",

		    obs, start, end);

	pr_info("system counter value: %"PRIu64" expected range [%"PRIu64", %"PRIu64"]\n",

		obs, start, end);

}

static void handle_abort(struct ucall *uc)

{

	TEST_FAIL("%s at %s:%ld", (const char *)uc->args[0],

		  __FILE__, uc->args[1]);

}

static void enter_guest(struct kvm_vm *vm)

{

	uint64_t start, end;

	struct ucall uc;

	int i;

	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {

		struct test_case *test = &test_cases[i];

		setup_system_counter(vm, test);

		start = host_read_guest_system_counter(test);

		vcpu_run(vm, VCPU_ID);

		end = host_read_guest_system_counter(test);

		switch (get_ucall(vm, VCPU_ID, &uc)) {

		case UCALL_SYNC:

			handle_sync(&uc, start, end);

			break;

		case UCALL_ABORT:

			handle_abort(&uc);

			return;

		default:

			TEST_ASSERT(0, "unhandled ucall %ld\n",

				    get_ucall(vm, VCPU_ID, &uc));

		}

	}

}

int main(void)

{

	struct kvm_vm *vm;

	vm = vm_create_default(VCPU_ID, 0, guest_main);

	check_preconditions(vm);

	ucall_init(vm, NULL);

	enter_guest(vm);

	kvm_vm_free(vm);

}