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

From: Atish Patra <atishp@rivosinc.com>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: linux-kernel@vger.kernel.org, Anup Patel <anup@brainfault.org>,
	Ajay Kaher <akaher@vmware.com>,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	Alexey Makhalov <amakhalov@vmware.com>,
	Conor Dooley <conor.dooley@microchip.com>,
	Juergen Gross <jgross@suse.com>,
	kvm-riscv@lists.infradead.org, kvm@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org,
	Mark Rutland <mark.rutland@arm.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Shuah Khan <shuah@kernel.org>,
	virtualization@lists.linux.dev,
	VMware PV-Drivers Reviewers <pv-drivers@vmware.com>,
	Will Deacon <will@kernel.org>,
	x86@kernel.org
Subject: Re: [PATCH v5 21/22] KVM: riscv: selftests: Add a test for PMU snapshot functionality
Date: Tue, 9 Apr 2024 15:52:40 -0700	[thread overview]
Message-ID: <8748dbed-d105-4f26-a808-667c3b56c8ec@rivosinc.com> (raw)
In-Reply-To: <20240405-4e840120e8117c286cb593f9@orel>

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