[PATCH v4 15/15] KVM: riscv: selftests: Add a test for counter overflow

[Atish Patra <atishp@rivosinc.com>]

Add a test for verifying overflow interrupt. Currently, it relies on
overflow support on cycle/instret events. This test works for cycle/
instret events which support sampling via hpmcounters on the platform.
There are no ISA extensions to detect if a platform supports that. Thus,
this test will fail on platform with virtualization but doesn't
support overflow on these two events.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 tools/testing/selftests/kvm/riscv/sbi_pmu.c | 126 +++++++++++++++++++-
 1 file changed, 125 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/riscv/sbi_pmu.c b/tools/testing/selftests/kvm/riscv/sbi_pmu.c
index 8ea2a6db6610..c0264c636054 100644
--- a/tools/testing/selftests/kvm/riscv/sbi_pmu.c
+++ b/tools/testing/selftests/kvm/riscv/sbi_pmu.c
@@ -8,6 +8,7 @@
  * Copyright (c) 2024, Rivos Inc.
  */
 
+#include "asm/csr.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -16,6 +17,7 @@
 #include "kvm_util.h"
 #include "test_util.h"
 #include "processor.h"
+#include "arch_timer.h"
 
 /* Maximum counters (firmware + hardware)*/
 #define RISCV_MAX_PMU_COUNTERS 64
@@ -26,6 +28,11 @@ union sbi_pmu_ctr_info ctrinfo_arr[RISCV_MAX_PMU_COUNTERS];
 static void *snapshot_gva;
 static vm_paddr_t snapshot_gpa;
 
+static int pmu_irq = IRQ_PMU_OVF;
+
+static int vcpu_shared_irq_count;
+static int counter_in_use;
+
 /* Cache the available counters in a bitmask */
 static unsigned long counter_mask_available;
 
@@ -69,7 +76,9 @@ unsigned long pmu_csr_read_num(int csr_num)
 #undef switchcase_csr_read
 }
 
-static inline void dummy_func_loop(int iter)
+static void stop_counter(unsigned long counter, unsigned long stop_flags);
+
+static inline void dummy_func_loop(uint64_t iter)
 {
 	int i = 0;
 
@@ -88,6 +97,26 @@ static void guest_illegal_exception_handler(struct ex_regs *regs)
 	regs->epc += 4;
 }
 
+static void guest_irq_handler(struct ex_regs *regs)
+{
+	unsigned int irq_num = regs->cause & ~CAUSE_IRQ_FLAG;
+	struct riscv_pmu_snapshot_data *snapshot_data = snapshot_gva;
+	unsigned long overflown_mask;
+
+	/* Stop all counters first to avoid further interrupts */
+	sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, 0, 1UL << counter_in_use,
+		  SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT, 0, 0, 0);
+
+	csr_clear(CSR_SIP, BIT(pmu_irq));
+
+	overflown_mask = READ_ONCE(snapshot_data->ctr_overflow_mask);
+	GUEST_ASSERT(overflown_mask & (1UL << counter_in_use));
+
+	/* Validate that we are in the correct irq handler */
+	GUEST_ASSERT_EQ(irq_num, pmu_irq);
+	WRITE_ONCE(vcpu_shared_irq_count, vcpu_shared_irq_count+1);
+}
+
 static unsigned long get_counter_index(unsigned long cbase, unsigned long cmask,
 				       unsigned long cflags,
 				       unsigned long event)
@@ -263,6 +292,32 @@ static void test_pmu_event_snapshot(unsigned long event)
 	stop_counter(counter, SBI_PMU_STOP_FLAG_RESET);
 }
 
+static void test_pmu_event_overflow(unsigned long event)
+{
+	unsigned long counter;
+	unsigned long counter_value_post;
+	unsigned long counter_init_value = ULONG_MAX - 10000;
+	struct riscv_pmu_snapshot_data *snapshot_data = snapshot_gva;
+
+	counter = get_counter_index(0, counter_mask_available, 0, event);
+	counter_in_use = counter;
+
+	/* The counter value is updated w.r.t relative index of cbase passed to start/stop */
+	WRITE_ONCE(snapshot_data->ctr_values[0], counter_init_value);
+	start_counter(counter, SBI_PMU_START_FLAG_INIT_FROM_SNAPSHOT, 0);
+	dummy_func_loop(10000);
+	udelay(msecs_to_usecs(2000));
+	/* irq handler should have stopped the counter */
+
+	counter_value_post = READ_ONCE(snapshot_data->ctr_values[counter_in_use]);
+	/* The counter value after stopping should be less the init value due to overflow */
+	__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_counter(counter, SBI_PMU_STOP_FLAG_RESET);
+}
+
 static void test_invalid_event(void)
 {
 	struct sbiret ret;
@@ -361,6 +416,43 @@ static void test_pmu_events_snaphost(int cpu)
 	GUEST_DONE();
 }
 
+static void test_pmu_events_overflow(int cpu)
+{
+	long out_val = 0;
+	bool probe;
+	int num_counters = 0;
+	unsigned long sbi_impl_version;
+
+	probe = guest_sbi_probe_extension(SBI_EXT_PMU, &out_val);
+	GUEST_ASSERT(probe && out_val == 1);
+
+	sbi_impl_version = get_host_sbi_impl_version();
+	if (sbi_impl_version >= sbi_mk_version(2, 0))
+		__GUEST_ASSERT(0, "SBI implementation version doesn't support PMU Snapshot");
+
+	snapshot_set_shmem(snapshot_gpa, 0);
+	csr_set(CSR_IE, BIT(pmu_irq));
+	local_irq_enable();
+
+	/* Get the counter details */
+	num_counters = get_num_counters();
+	update_counter_info(num_counters);
+
+	/*
+	 * Qemu supports overflow for cycle/instruction.
+	 * This test may fail on any platform that do not support overflow for these two events.
+	 */
+	test_pmu_event_overflow(SBI_PMU_HW_CPU_CYCLES);
+	GUEST_ASSERT_EQ(vcpu_shared_irq_count, 1);
+
+	/* Renable the interrupt again for another event */
+	csr_set(CSR_IE, BIT(pmu_irq));
+	test_pmu_event_overflow(SBI_PMU_HW_INSTRUCTIONS);
+	GUEST_ASSERT_EQ(vcpu_shared_irq_count, 2);
+
+	GUEST_DONE();
+}
+
 static void run_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct ucall uc;
@@ -449,6 +541,35 @@ static void test_vm_events_snapshot_test(void *guest_code)
 	test_vm_destroy(vm);
 }
 
+static void test_vm_events_overflow(void *guest_code)
+{
+	struct kvm_vm *vm = NULL;
+	struct kvm_vcpu *vcpu = NULL;
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+	__TEST_REQUIRE(__vcpu_has_ext(vcpu, RISCV_SBI_EXT_REG(KVM_RISCV_SBI_EXT_PMU)),
+				   "SBI PMU not available, skipping test");
+
+	__TEST_REQUIRE(__vcpu_has_ext(vcpu, RISCV_ISA_EXT_REG(KVM_RISCV_ISA_EXT_SSCOFPMF)),
+				   "Sscofpmf is not available, skipping overflow test");
+
+
+	test_vm_setup_snapshot_mem(vm, vcpu);
+	vm_init_vector_tables(vm);
+	vm_install_interrupt_handler(vm, guest_irq_handler);
+
+	vcpu_init_vector_tables(vcpu);
+	/* Initialize guest timer frequency. */
+	vcpu_get_reg(vcpu, RISCV_TIMER_REG(frequency), &timer_freq);
+	sync_global_to_guest(vm, timer_freq);
+
+	vcpu_args_set(vcpu, 1, 0);
+
+	run_vcpu(vcpu);
+
+	test_vm_destroy(vm);
+}
+
 int main(void)
 {
 	test_vm_basic_test(test_pmu_basic_sanity);
@@ -460,5 +581,8 @@ int main(void)
 	test_vm_events_snapshot_test(test_pmu_events_snaphost);
 	pr_info("SBI PMU event verification with snapshot test : PASS\n");
 
+	test_vm_events_overflow(test_pmu_events_overflow);
+	pr_info("SBI PMU event verification with overflow test : PASS\n");
+
 	return 0;
 }
-- 
2.34.1