Re: [PATCH v5 21/22] KVM: riscv: selftests: Add a test for PMU snapshot functionality

Atish Patra
2024-04-09T22:52:44Z

On 4/5/24 06:11, Andrew Jones wrote:
> On Wed, Apr 03, 2024 at 01:04:50AM -0700, Atish Patra wrote:
>> Verify PMU snapshot functionality by setting up the shared memory
>> correctly and reading the counter values from the shared memory
>> instead of the CSR.
>>
>> Reviewed-by: Anup Patel <anup@brainfault.org>
>> Signed-off-by: Atish Patra <atishp@rivosinc.com>
>> ---
>> .../testing/selftests/kvm/include/riscv/sbi.h | 25 ++++
>> .../selftests/kvm/lib/riscv/processor.c | 12 ++
>> .../selftests/kvm/riscv/sbi_pmu_test.c | 127 ++++++++++++++++++
>> 3 files changed, 164 insertions(+)
>>
>> diff --git a/tools/testing/selftests/kvm/include/riscv/sbi.h b/tools/testing/selftests/kvm/include/riscv/sbi.h
>> index 6675ca673c77..8c98bd99d450 100644
>> --- a/tools/testing/selftests/kvm/include/riscv/sbi.h
>> +++ b/tools/testing/selftests/kvm/include/riscv/sbi.h
>> @@ -8,6 +8,12 @@
>> #ifndef SELFTEST_KVM_SBI_H
>> #define SELFTEST_KVM_SBI_H
>>
>> +/* SBI spec version fields */
>> +#define SBI_SPEC_VERSION_DEFAULT 0x1
>> +#define SBI_SPEC_VERSION_MAJOR_SHIFT 24
>> +#define SBI_SPEC_VERSION_MAJOR_MASK 0x7f
>> +#define SBI_SPEC_VERSION_MINOR_MASK 0xffffff
>> +
>> /* SBI return error codes */
>> #define SBI_SUCCESS 0
>> #define SBI_ERR_FAILURE -1
>> @@ -33,6 +39,9 @@ enum sbi_ext_id {
>> };
>>
>> enum sbi_ext_base_fid {
>> + SBI_EXT_BASE_GET_SPEC_VERSION = 0,
>> + SBI_EXT_BASE_GET_IMP_ID,
>> + SBI_EXT_BASE_GET_IMP_VERSION,
>> SBI_EXT_BASE_PROBE_EXT = 3,
>> };
>> enum sbi_ext_pmu_fid {
>> @@ -60,6 +69,12 @@ union sbi_pmu_ctr_info {
>> };
>> };
>>
>> +struct riscv_pmu_snapshot_data {
>> + u64 ctr_overflow_mask;
>> + u64 ctr_values[64];
>> + u64 reserved[447];
>> +};
>> +
>> struct sbiret {
>> long error;
>> long value;
>> @@ -113,4 +128,14 @@ struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,
>>
>> bool guest_sbi_probe_extension(int extid, long *out_val);
>>
>> +/* Make SBI version */
>> +static inline unsigned long sbi_mk_version(unsigned long major,
>> + unsigned long minor)
>> +{
>> + return ((major & SBI_SPEC_VERSION_MAJOR_MASK) <<
>> + SBI_SPEC_VERSION_MAJOR_SHIFT) | minor;
>
> Should also also mask 'minor'. I see this matches what we have in the
> kernel so we should fix it there too.
>

Nice catch. I fixed it in both places.

>> +}
>> +
>> +unsigned long get_host_sbi_spec_version(void);
>> +
>> #endif /* SELFTEST_KVM_SBI_H */
>> diff --git a/tools/testing/selftests/kvm/lib/riscv/processor.c b/tools/testing/selftests/kvm/lib/riscv/processor.c
>> index e8211f5d6863..ccb35573749c 100644
>> --- a/tools/testing/selftests/kvm/lib/riscv/processor.c
>> +++ b/tools/testing/selftests/kvm/lib/riscv/processor.c
>> @@ -502,3 +502,15 @@ bool guest_sbi_probe_extension(int extid, long *out_val)
>>
>> return true;
>> }
>> +
>> +unsigned long get_host_sbi_spec_version(void)
>> +{
>> + struct sbiret ret;
>> +
>> + ret = sbi_ecall(SBI_EXT_BASE, SBI_EXT_BASE_GET_SPEC_VERSION, 0,
>> + 0, 0, 0, 0, 0);
>> +
>> + GUEST_ASSERT(!ret.error);
>> +
>> + return ret.value;
>> +}
>> diff --git a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> index 8e7c7a3172d8..7d195be5c3d9 100644
>> --- a/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> +++ b/tools/testing/selftests/kvm/riscv/sbi_pmu_test.c
>> @@ -19,6 +19,11 @@
>> #define RISCV_MAX_PMU_COUNTERS 64
>> union sbi_pmu_ctr_info ctrinfo_arr[RISCV_MAX_PMU_COUNTERS];
>>
>> +/* Snapshot shared memory data */
>> +#define PMU_SNAPSHOT_GPA_BASE BIT(30)
>> +static void *snapshot_gva;
>> +static vm_paddr_t snapshot_gpa;
>> +
>> /* Cache the available counters in a bitmask */
>> static unsigned long counter_mask_available;
>>
>> @@ -178,6 +183,32 @@ static unsigned long read_counter(int idx, union sbi_pmu_ctr_info ctrinfo)
>> return counter_val;
>> }
>>
>> +static inline void verify_sbi_requirement_assert(void)
>> +{
>> + long out_val = 0;
>> + bool probe;
>> +
>> + probe = guest_sbi_probe_extension(SBI_EXT_PMU, &out_val);
>> + GUEST_ASSERT(probe && out_val == 1);
>> +
>> + if (get_host_sbi_spec_version() < sbi_mk_version(2, 0))
>> + __GUEST_ASSERT(0, "SBI implementation version doesn't support PMU Snapshot");
>> +}
>
> It's a pity we can't check the SBI spec version that KVM is advertising
> from KVM userspace. Normally we'd want to check something like this at
> the start of the test with TEST_REQUIRE() before running a VCPU in order
> to generate a skip exit.
>

Agreed. I will send a separate series for that as it is an ABI change.

> (We probably should allow reading and even writing the SBI spec version
> from the VMM in order to better support migration.)
>

How that would work for SBI spec version write use case ? For migraiton,
you can't go back to older SBI versions in the host. Isn't it ?

Considering this case your VM is running with PMU snapshot as the host
has SBI v2.0. It can't be migrated to v1.0 and expecting it work. Correct ?

>> +
>> +static void snapshot_set_shmem(vm_paddr_t gpa, unsigned long flags)
>> +{
>> + unsigned long lo = (unsigned long)gpa;
>> +#if __riscv_xlen == 32
>> + unsigned long hi = (unsigned long)(gpa >> 32);
>> +#else
>> + unsigned long hi = gpa == -1 ? -1 : 0;
>> +#endif
>> + struct sbiret ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_SNAPSHOT_SET_SHMEM,
>> + lo, hi, flags, 0, 0, 0);
>> +
>> + GUEST_ASSERT(ret.value == 0 && ret.error == 0);
>> +}
>> +
>> static void test_pmu_event(unsigned long event)
>> {
>> unsigned long counter;
>> @@ -210,6 +241,41 @@ static void test_pmu_event(unsigned long event)
>> stop_reset_counter(counter, 0);
>> }
>>
>> +static void test_pmu_event_snapshot(unsigned long event)
>> +{
>> + unsigned long counter;
>> + unsigned long counter_value_pre, counter_value_post;
>> + unsigned long counter_init_value = 100;
>> + struct riscv_pmu_snapshot_data *snapshot_data = snapshot_gva;
>> +
>> + counter = get_counter_index(0, counter_mask_available, 0, event);
>> + counter_value_pre = read_counter(counter, ctrinfo_arr[counter]);
>> +
>> + /* Do not set the initial value */
>> + start_counter(counter, 0, 0);
>> + dummy_func_loop(10000);
>> + stop_counter(counter, SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT);
>> +
>> + /* The counter value is updated w.r.t relative index of cbase */
>> + counter_value_post = READ_ONCE(snapshot_data->ctr_values[0]);
>> + __GUEST_ASSERT(counter_value_post > counter_value_pre,
>> + "counter_value_post %lx counter_value_pre %lx\n",
>> + counter_value_post, counter_value_pre);
>> +
>> + /* Now set the initial value and compare */
>> + WRITE_ONCE(snapshot_data->ctr_values[0], counter_init_value);
>> + start_counter(counter, SBI_PMU_START_FLAG_INIT_SNAPSHOT, 0);
>> + dummy_func_loop(10000);
>> + stop_counter(counter, SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT);
>> +
>> + counter_value_post = READ_ONCE(snapshot_data->ctr_values[0]);
>> + __GUEST_ASSERT(counter_value_post > counter_init_value,
>> + "counter_value_post %lx counter_init_value %lx for counter\n",
>> + counter_value_post, counter_init_value);
>> +
>> + stop_reset_counter(counter, 0);
>> +}
>> +
>> static void test_invalid_event(void)
>> {
>> struct sbiret ret;
>> @@ -272,6 +338,34 @@ static void test_pmu_basic_sanity(void)
>> GUEST_DONE();
>> }
>>
>> +static void test_pmu_events_snaphost(void)
>> +{
>> + int num_counters = 0;
>> + struct riscv_pmu_snapshot_data *snapshot_data = snapshot_gva;
>> + int i;
>> +
>> + /* Verify presence of SBI PMU and minimum requrired SBI version */
>> + verify_sbi_requirement_assert();
>> +
>> + snapshot_set_shmem(snapshot_gpa, 0);
>> +
>> + /* Get the counter details */
>> + num_counters = get_num_counters();
>> + update_counter_info(num_counters);
>> +
>> + /* Validate shared memory access */
>> + GUEST_ASSERT_EQ(READ_ONCE(snapshot_data->ctr_overflow_mask), 0);
>> + for (i = 0; i < num_counters; i++) {
>> + if (counter_mask_available & (BIT(i)))
>> + GUEST_ASSERT_EQ(READ_ONCE(snapshot_data->ctr_values[i]), 0);
>> + }
>> + /* Only these two events are guranteed to be present */
>> + test_pmu_event_snapshot(SBI_PMU_HW_CPU_CYCLES);
>> + test_pmu_event_snapshot(SBI_PMU_HW_INSTRUCTIONS);
>> +
>> + GUEST_DONE();
>> +}
>> +
>> static void run_vcpu(struct kvm_vcpu *vcpu)
>> {
>> struct ucall uc;
>> @@ -328,13 +422,46 @@ static void test_vm_events_test(void *guest_code)
>> test_vm_destroy(vm);
>> }
>>
>> +static void test_vm_setup_snapshot_mem(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
>> +{
>> + /* PMU Snapshot requires single page only */
>> + vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, PMU_SNAPSHOT_GPA_BASE, 1, 1, 0);
>> + /* PMU_SNAPSHOT_GPA_BASE is identity mapped */
>> + virt_map(vm, PMU_SNAPSHOT_GPA_BASE, PMU_SNAPSHOT_GPA_BASE, 1);
>> +
>> + snapshot_gva = (void *)(PMU_SNAPSHOT_GPA_BASE);
>> + snapshot_gpa = addr_gva2gpa(vcpu->vm, (vm_vaddr_t)snapshot_gva);
>> + sync_global_to_guest(vcpu->vm, snapshot_gva);
>> + sync_global_to_guest(vcpu->vm, snapshot_gpa);
>> +}
>> +
>> +static void test_vm_events_snapshot_test(void *guest_code)
>> +{
>> + struct kvm_vm *vm = NULL;
>> + struct kvm_vcpu *vcpu;
>> +
>> + vm = vm_create_with_one_vcpu(&vcpu, guest_code);
>> + __TEST_REQUIRE(__vcpu_has_sbi_ext(vcpu, KVM_RISCV_SBI_EXT_PMU),
>> + "SBI PMU not available, skipping test");
>> +
>> + test_vm_setup_snapshot_mem(vm, vcpu);
>> +
>> + run_vcpu(vcpu);
>> +
>> + test_vm_destroy(vm);
>> +}
>> +
>> int main(void)
>> {
>> + pr_info("SBI PMU basic test : starting\n");
>> test_vm_basic_test(test_pmu_basic_sanity);
>> pr_info("SBI PMU basic test : PASS\n");
>>
>> test_vm_events_test(test_pmu_events);
>> pr_info("SBI PMU event verification test : PASS\n");
>>
>> + test_vm_events_snapshot_test(test_pmu_events_snaphost);
>> + pr_info("SBI PMU event verification with snapshot test : PASS\n");
>> +
>> return 0;
>> }
>> --
>> 2.34.1
>>
>
> Since my comments are a bit out-of-scope for this patch,
>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
>
> Thanks,
> drew