Commit 3f9808ca authored by Oliver Upton's avatar Oliver Upton Committed by Paolo Bonzini

selftests: KVM: Introduce system counter offset test

Introduce a KVM selftest to verify that userspace manipulation of the
TSC (via the new vCPU attribute) results in the correct behavior within
the guest.
Reviewed-by: default avatarAndrew Jones <drjones@redhat.com>
Signed-off-by: default avatarOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-6-oupton@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c8955134
......@@ -184,37 +184,50 @@ TSC is then derived by the following equation:
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.
......@@ -54,3 +54,4 @@
/set_memory_region_test
/steal_time
/kvm_binary_stats_test
/system_counter_offset_test
......@@ -86,6 +86,7 @@ TEST_GEN_PROGS_x86_64 += rseq_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);
}
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